DOCUMENT NO
577000403 ndash MGT100 ndash GGR ndash 107 DOCUMENT TITLE
DECOMMISSIONING PROGRAMME
GREATER GABBARD OFFSHORE
WIND FARM PROJECT
Fluor Project No 577000 Airtricity Project No 403
CONTROLLED COPY NO ______
1 310807 58 Issued for Secretary of State Sign off
CJH CH GM JCH
0 010607 53 Issued for Approval
CJH CH GM JCH
REV DATE PAGES DESCRIPTION BY CHKD APPR
FLUOR APPR
AIRTRICITY
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Table of Contents
10 INTRODUCTION4
20 EXECUTIVE SUMMARY 4
30 BACKGROUND INFORMATION 7
31 Project Status 7
32 Project Overview 7
33 Layout of Wind Farm and Ancillary Works 10
34 Site Characteristics11
341 Physical Characteristics 11
35 Relevant Projects and Activities 18 351 Offshore Wind Farms 18
352 Marine Aggregate Extraction20 353 Disposal of Dredged Material21 354 Subsea Cables 22
355 Oil and Gas 23 356 Fishing Activity 24
357 Shipping Activity 25
36 Nature Conservation 26
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED29
41 Guiding Principles 29
42 Proposed Decommissioning31
421 Offshore Wind Turbines 32
422 Turbine Foundations amp Transition Pieces 35 423 Transformer Platforms 39
424 Anemometry Masts41
425 Cabling43
426 Scour Protection46
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES48
51 Wind TurbinesGenerating Equipment 48
52 Foundations49
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
53 Transformer Platforms 50
54 Anemometry Masts50
55 Cables50
56 Scour Protection50
57 Waste Management50
58 Lighting and Marking 51
60 RE-POWERING52
70 ENVIRONMENTAL IMPACT ASSESSMENT 52
80 CONSULTATIONS WITH INTERESTED PARTIES 53
90 SCHEDULE AND THE REVIEW PROCESS 54
100 SEA-BED CLEARANCE55
110 RESTORATION OF THE SITE56
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE 56
130 SUPPORTING STUDIES 57
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT58
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT 58
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
10 INTRODUCTION
The Greater Gabbard Offshore Wind Farm will feature 140 turbines generating a total capacity of 500MW Covering approximately 147km2 the project will be located some 26km off the Suffolk coast adjacent to sandbanks known as Inner Gabbard and The Galloper
The wind farm is being developed by Greater Gabbard Offshore Winds Limited (GGOWL) a company formed specifically to develop finance construct operate and decommission the project The company is jointly owned by Airtricity Holdings (UK) Limited and Fluor International Limited
GGOWL obtained consent under Section 36 of the Electricity Act 1989 in February 2007 for the Greater Gabbard Offshore Wind Farm At this time the DTI also issued GGOWL a notice under Section 105(2) of the Energy Act 2004 regarding the requirement to prepare and obtain approval for the decommissioning programme for the project prior to construction commencement
This document presents the decommissioning programme for the Greater Gabbard Offshore Wind Farm and is being submitted for approval in accordance with the Energy Act 2004 requirements The decommissioning programme is informed and supported by the Environmental Impact Assessment (EIA) for the Greater Gabbard Offshore Wind Farm Project that was submitted to DTI in October 2005 The decommissioning programme addresses all components of the wind farm below mean high water springs The onshore aspects of the project and the associated decommissioning requirements fall under the planning permission granted under Section 57 Town and Country Planning Act 1990 by Suffolk Coastal District Council
Whilst the design life for the wind turbines is 25 years the lease term for the project is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term Nonetheless GGOWL acknowledges the UKrsquos international obligations requiring installations to be decommissioned as soon as is reasonably practicable This programme therefore sets out the measures for decommissioning the project at the end of the design life of the equipment during year 25 It is expected that as this time approaches GGOWL will seek approval from the Secretary of State to delay the decommissioning work in favour of re-powering the project
The programme is to be reviewed and revised as necessary throughout the lifecycle of the project to reflect changing circumstances and regulatory requirements and to incorporate improvements in knowledge and understanding of the marine environment and advances in technology and working practices
20 EXECUTIVE SUMMARY
The Energy Act 2004 requires that GGOWL prepares and ultimately carries out a decommissioning programme for the Greater Gabbard Offshore Wind Farm This document
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
constitutes the preliminary decommissioning programme for the project and is submitted for approval prior to the construction of the wind farm
The programme is informed and supported by the Environmental Impact Assessment (EIA) carried out for the Greater Gabbard Offshore Wind Farm Project The resulting Environmental Statement was submitted as part of the projectrsquos application for consent in October 2005 The Environmental Statement provides detailed analysis of the baseline physical biological and human environment The assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are consistent with those presented in this document A CD version of the Environmental Statement is provided as Annex A to this document
The programme is also informed by the outcome of the Appropriate Assessment undertaken prior to the consent of the wind farm This document is also provided as Annex B
In considering appropriate decommissioning provisions GGOWL have sought to adhere to the following key principles
bull Safety for all at all times
bull Consideration of the rights and needs of legitimate users of the sea
bull Minimise environmental impact
bull Promote sustainable development
bull Adhere to the Polluter Pays Principle
bull Maximise the reuse of materials
bull Commercial viability
bull Practical integrity
The following key documents have also informed the provisions presented
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
GGOWLrsquos starting assumption for establishing the extent of decommissioning is complete removal This assumption has been assessed against the guiding principles listed above and where appropriate alternative solutions have been identified A summary of the proposals for decommissioning the offshore components of the Greater Gabbard Offshore Wind Farm are outlined in the table below
Component Decommissioning Proposal
Wind Turbinegenerating equipment Complete removal from site
Foundations (wind turbine met mast transformer platforms) Cut off at or below seabed and removed
Cables (inter-array and export) Left in situ
Anemometry masts Complete removal of structure
Transformer platforms Complete removal of topside
The measures proposed to decommission the installations as described above reflect the strong emphasis GGOWL puts on minimising risks to safety and to the environment As such GGOWL has sought practical solutions that involve minimal offshore operations
In the absence of re-powering GGOWL intends to begin decommissioning the project at year 25 It is intended that this process offshore be completed over a period of 300 days
The decommissioning programme as currently proposed is to be reviewed and revised throughout the lifecycle of the project to reflect changing circumstances and regulatory requirements and to incorporate improvements in knowledge and understanding of the marine environment and advances in technology and working practices A formal schedule for review is proposed where year 23 is identified as the final opportunity for a thorough review and consultation process
GGOWLrsquos approach to consultation about these works mirrors that undertaken during the EIA process for the project where importance is attached to early and open communication
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
with all key stakeholders Key stakeholders will have the opportunity to input into the draft decommissioning programme and to consider the final programme to be agreed prior to decommissioning Appropriate consultation and notification will be undertaken prior to the works taking place
A cost estimate for the programme has been derived based on the equipment and personnel requirements and the duration of the works Financial security provisions have been carefully considered to ensure that this liability will be met Details of the cost and financial aspects of the proposals are provided as Annex C to this programme
30 BACKGROUND INFORMATION
31 Project Status
The Greater Gabbard Offshore Wind Farm was awarded through the Round Two site allocation process in December 2003
An Environmental Impact Assessment was carried out and an application for consent for the project submitted in October 2005 The project was awarded the following consents in February 2007
bull Section 36 Electricity Act 1989 (construction and operation of the wind turbines offshore transformer stations and met masts granted by DTI)
bull Section 5 Food and Environment Protection Act 1985 (installation of foundations of offshore structures rock armouring scour protection etc granted by DEFRA)
bull Section 34 Coast Protection Act 1949 (obstruction to navigation works granted by DEFRA)
bull Section 36A Electricity Act 1989 (navigation extinguishment declaration granted by DTI)
Planning permission has also been received under Section 57 of the Town and Country Planning Act 1990 for the onshore works at Sizewell
The project is scheduled to commence construction offshore in late 2008
32 Project Overview
The wind farm is to be located 26km off the Suffolk coast adjacent to two sand banks known as Inner Gabbard and The Galloper The project comprises 140 wind turbines which will be installed over a total area of 147km2 and will generate a maximum capacity of 500MW The power will be brought to shore at Sizewell where an onshore sub-station will be located to connect the wind farm to the National Grid Figure 1 below shows the sitersquos location boundaries and the cable route to shore
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 1 Greater Gabbard Site Boundaries
The site coordinates are as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Offshore transformer platforms will transform the turbine interconnection voltage from 33kV to 132kV for transmission ashore by up to four export cables These offshore sub-stations will have typical dimensions in the order of 20m length x 20m width x 15m height
Up to six permanent meteorological masts of a nominal height of up to 105m will also be constructed
The foundations for the wind turbines will be steel monopiles of up to 65m diameter driven into the seabed using a hydraulic hammer from a jack-up bargedrilling rig or purpose built installation vessel Scour protection in the form of rock gravel or frond mats may be used
Transition sections will be used to connect the wind turbine tower to the foundation by means of a grouted joint or a flanged connection
The foundations for the meteorological masts will consist of a steel monopile with a diameter of approximately 25m Scour protection may be required and would be similar to that used for wind turbine monopiles
The foundations for the offshore substations will be based on a jacket structure which will be secured to the seabed with piles
If required the use of scour protection around the foundations may consist of loose rock or rough gravel to be installed by means of grab and drop or bulldozed over the side of a vessel The use of mattresses for protection may also be used and installed by means of lowering from a vessel to the base of the foundation
The turbines will be connected to the offshore sub-stations via a network of 33kV cables (inter-array cables) that are laid between the wind turbines and the offshore sub-stations Up to four subsea 132kV cables (export cables) will connect the wind farm to the shore
The inter-array and export cables are likely to be buried using an underwater cable plough that executes a simultaneous lay and burial technique by lifting a wedge of sediment allowing the cable to fall into this trench and then folding the sediment back on top of the cable In exceptional circumstances and only following written authorisation from DEFRA cable burial Remote Operated Vehicle (ROV) may be used This utilises high-pressure water jets to fluidise a narrow trench into which the cable is located The jetted sediments settle back into the trench
The inter-tidal cables may be installed from a barge or jack-up which is either beached or moored near Sizewell beach The cable will be pulled beneath the inter-tidal zone using a directional drilling technique either beginning at the start of the run out to sea or at the end of the run from sea Near shore and deep water lay may be separate operations
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33 Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm The final layout will be determined in agreement with DTI prior to construction
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Page 42 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
Page 43 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Table of Contents
10 INTRODUCTION4
20 EXECUTIVE SUMMARY 4
30 BACKGROUND INFORMATION 7
31 Project Status 7
32 Project Overview 7
33 Layout of Wind Farm and Ancillary Works 10
34 Site Characteristics11
341 Physical Characteristics 11
35 Relevant Projects and Activities 18 351 Offshore Wind Farms 18
352 Marine Aggregate Extraction20 353 Disposal of Dredged Material21 354 Subsea Cables 22
355 Oil and Gas 23 356 Fishing Activity 24
357 Shipping Activity 25
36 Nature Conservation 26
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED29
41 Guiding Principles 29
42 Proposed Decommissioning31
421 Offshore Wind Turbines 32
422 Turbine Foundations amp Transition Pieces 35 423 Transformer Platforms 39
424 Anemometry Masts41
425 Cabling43
426 Scour Protection46
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES48
51 Wind TurbinesGenerating Equipment 48
52 Foundations49
Page 2 of 58
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53 Transformer Platforms 50
54 Anemometry Masts50
55 Cables50
56 Scour Protection50
57 Waste Management50
58 Lighting and Marking 51
60 RE-POWERING52
70 ENVIRONMENTAL IMPACT ASSESSMENT 52
80 CONSULTATIONS WITH INTERESTED PARTIES 53
90 SCHEDULE AND THE REVIEW PROCESS 54
100 SEA-BED CLEARANCE55
110 RESTORATION OF THE SITE56
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE 56
130 SUPPORTING STUDIES 57
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT58
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT 58
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT58
Page 3 of 58
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10 INTRODUCTION
The Greater Gabbard Offshore Wind Farm will feature 140 turbines generating a total capacity of 500MW Covering approximately 147km2 the project will be located some 26km off the Suffolk coast adjacent to sandbanks known as Inner Gabbard and The Galloper
The wind farm is being developed by Greater Gabbard Offshore Winds Limited (GGOWL) a company formed specifically to develop finance construct operate and decommission the project The company is jointly owned by Airtricity Holdings (UK) Limited and Fluor International Limited
GGOWL obtained consent under Section 36 of the Electricity Act 1989 in February 2007 for the Greater Gabbard Offshore Wind Farm At this time the DTI also issued GGOWL a notice under Section 105(2) of the Energy Act 2004 regarding the requirement to prepare and obtain approval for the decommissioning programme for the project prior to construction commencement
This document presents the decommissioning programme for the Greater Gabbard Offshore Wind Farm and is being submitted for approval in accordance with the Energy Act 2004 requirements The decommissioning programme is informed and supported by the Environmental Impact Assessment (EIA) for the Greater Gabbard Offshore Wind Farm Project that was submitted to DTI in October 2005 The decommissioning programme addresses all components of the wind farm below mean high water springs The onshore aspects of the project and the associated decommissioning requirements fall under the planning permission granted under Section 57 Town and Country Planning Act 1990 by Suffolk Coastal District Council
Whilst the design life for the wind turbines is 25 years the lease term for the project is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term Nonetheless GGOWL acknowledges the UKrsquos international obligations requiring installations to be decommissioned as soon as is reasonably practicable This programme therefore sets out the measures for decommissioning the project at the end of the design life of the equipment during year 25 It is expected that as this time approaches GGOWL will seek approval from the Secretary of State to delay the decommissioning work in favour of re-powering the project
The programme is to be reviewed and revised as necessary throughout the lifecycle of the project to reflect changing circumstances and regulatory requirements and to incorporate improvements in knowledge and understanding of the marine environment and advances in technology and working practices
20 EXECUTIVE SUMMARY
The Energy Act 2004 requires that GGOWL prepares and ultimately carries out a decommissioning programme for the Greater Gabbard Offshore Wind Farm This document
Page 4 of 58
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constitutes the preliminary decommissioning programme for the project and is submitted for approval prior to the construction of the wind farm
The programme is informed and supported by the Environmental Impact Assessment (EIA) carried out for the Greater Gabbard Offshore Wind Farm Project The resulting Environmental Statement was submitted as part of the projectrsquos application for consent in October 2005 The Environmental Statement provides detailed analysis of the baseline physical biological and human environment The assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are consistent with those presented in this document A CD version of the Environmental Statement is provided as Annex A to this document
The programme is also informed by the outcome of the Appropriate Assessment undertaken prior to the consent of the wind farm This document is also provided as Annex B
In considering appropriate decommissioning provisions GGOWL have sought to adhere to the following key principles
bull Safety for all at all times
bull Consideration of the rights and needs of legitimate users of the sea
bull Minimise environmental impact
bull Promote sustainable development
bull Adhere to the Polluter Pays Principle
bull Maximise the reuse of materials
bull Commercial viability
bull Practical integrity
The following key documents have also informed the provisions presented
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
Page 5 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
GGOWLrsquos starting assumption for establishing the extent of decommissioning is complete removal This assumption has been assessed against the guiding principles listed above and where appropriate alternative solutions have been identified A summary of the proposals for decommissioning the offshore components of the Greater Gabbard Offshore Wind Farm are outlined in the table below
Component Decommissioning Proposal
Wind Turbinegenerating equipment Complete removal from site
Foundations (wind turbine met mast transformer platforms) Cut off at or below seabed and removed
Cables (inter-array and export) Left in situ
Anemometry masts Complete removal of structure
Transformer platforms Complete removal of topside
The measures proposed to decommission the installations as described above reflect the strong emphasis GGOWL puts on minimising risks to safety and to the environment As such GGOWL has sought practical solutions that involve minimal offshore operations
In the absence of re-powering GGOWL intends to begin decommissioning the project at year 25 It is intended that this process offshore be completed over a period of 300 days
The decommissioning programme as currently proposed is to be reviewed and revised throughout the lifecycle of the project to reflect changing circumstances and regulatory requirements and to incorporate improvements in knowledge and understanding of the marine environment and advances in technology and working practices A formal schedule for review is proposed where year 23 is identified as the final opportunity for a thorough review and consultation process
GGOWLrsquos approach to consultation about these works mirrors that undertaken during the EIA process for the project where importance is attached to early and open communication
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with all key stakeholders Key stakeholders will have the opportunity to input into the draft decommissioning programme and to consider the final programme to be agreed prior to decommissioning Appropriate consultation and notification will be undertaken prior to the works taking place
A cost estimate for the programme has been derived based on the equipment and personnel requirements and the duration of the works Financial security provisions have been carefully considered to ensure that this liability will be met Details of the cost and financial aspects of the proposals are provided as Annex C to this programme
30 BACKGROUND INFORMATION
31 Project Status
The Greater Gabbard Offshore Wind Farm was awarded through the Round Two site allocation process in December 2003
An Environmental Impact Assessment was carried out and an application for consent for the project submitted in October 2005 The project was awarded the following consents in February 2007
bull Section 36 Electricity Act 1989 (construction and operation of the wind turbines offshore transformer stations and met masts granted by DTI)
bull Section 5 Food and Environment Protection Act 1985 (installation of foundations of offshore structures rock armouring scour protection etc granted by DEFRA)
bull Section 34 Coast Protection Act 1949 (obstruction to navigation works granted by DEFRA)
bull Section 36A Electricity Act 1989 (navigation extinguishment declaration granted by DTI)
Planning permission has also been received under Section 57 of the Town and Country Planning Act 1990 for the onshore works at Sizewell
The project is scheduled to commence construction offshore in late 2008
32 Project Overview
The wind farm is to be located 26km off the Suffolk coast adjacent to two sand banks known as Inner Gabbard and The Galloper The project comprises 140 wind turbines which will be installed over a total area of 147km2 and will generate a maximum capacity of 500MW The power will be brought to shore at Sizewell where an onshore sub-station will be located to connect the wind farm to the National Grid Figure 1 below shows the sitersquos location boundaries and the cable route to shore
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Figure 1 Greater Gabbard Site Boundaries
The site coordinates are as follows
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Offshore transformer platforms will transform the turbine interconnection voltage from 33kV to 132kV for transmission ashore by up to four export cables These offshore sub-stations will have typical dimensions in the order of 20m length x 20m width x 15m height
Up to six permanent meteorological masts of a nominal height of up to 105m will also be constructed
The foundations for the wind turbines will be steel monopiles of up to 65m diameter driven into the seabed using a hydraulic hammer from a jack-up bargedrilling rig or purpose built installation vessel Scour protection in the form of rock gravel or frond mats may be used
Transition sections will be used to connect the wind turbine tower to the foundation by means of a grouted joint or a flanged connection
The foundations for the meteorological masts will consist of a steel monopile with a diameter of approximately 25m Scour protection may be required and would be similar to that used for wind turbine monopiles
The foundations for the offshore substations will be based on a jacket structure which will be secured to the seabed with piles
If required the use of scour protection around the foundations may consist of loose rock or rough gravel to be installed by means of grab and drop or bulldozed over the side of a vessel The use of mattresses for protection may also be used and installed by means of lowering from a vessel to the base of the foundation
The turbines will be connected to the offshore sub-stations via a network of 33kV cables (inter-array cables) that are laid between the wind turbines and the offshore sub-stations Up to four subsea 132kV cables (export cables) will connect the wind farm to the shore
The inter-array and export cables are likely to be buried using an underwater cable plough that executes a simultaneous lay and burial technique by lifting a wedge of sediment allowing the cable to fall into this trench and then folding the sediment back on top of the cable In exceptional circumstances and only following written authorisation from DEFRA cable burial Remote Operated Vehicle (ROV) may be used This utilises high-pressure water jets to fluidise a narrow trench into which the cable is located The jetted sediments settle back into the trench
The inter-tidal cables may be installed from a barge or jack-up which is either beached or moored near Sizewell beach The cable will be pulled beneath the inter-tidal zone using a directional drilling technique either beginning at the start of the run out to sea or at the end of the run from sea Near shore and deep water lay may be separate operations
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33 Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm The final layout will be determined in agreement with DTI prior to construction
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Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
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bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
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Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
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Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
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Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
Page 43 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
Page 45 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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53 Transformer Platforms 50
54 Anemometry Masts50
55 Cables50
56 Scour Protection50
57 Waste Management50
58 Lighting and Marking 51
60 RE-POWERING52
70 ENVIRONMENTAL IMPACT ASSESSMENT 52
80 CONSULTATIONS WITH INTERESTED PARTIES 53
90 SCHEDULE AND THE REVIEW PROCESS 54
100 SEA-BED CLEARANCE55
110 RESTORATION OF THE SITE56
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE 56
130 SUPPORTING STUDIES 57
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT58
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT 58
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT58
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10 INTRODUCTION
The Greater Gabbard Offshore Wind Farm will feature 140 turbines generating a total capacity of 500MW Covering approximately 147km2 the project will be located some 26km off the Suffolk coast adjacent to sandbanks known as Inner Gabbard and The Galloper
The wind farm is being developed by Greater Gabbard Offshore Winds Limited (GGOWL) a company formed specifically to develop finance construct operate and decommission the project The company is jointly owned by Airtricity Holdings (UK) Limited and Fluor International Limited
GGOWL obtained consent under Section 36 of the Electricity Act 1989 in February 2007 for the Greater Gabbard Offshore Wind Farm At this time the DTI also issued GGOWL a notice under Section 105(2) of the Energy Act 2004 regarding the requirement to prepare and obtain approval for the decommissioning programme for the project prior to construction commencement
This document presents the decommissioning programme for the Greater Gabbard Offshore Wind Farm and is being submitted for approval in accordance with the Energy Act 2004 requirements The decommissioning programme is informed and supported by the Environmental Impact Assessment (EIA) for the Greater Gabbard Offshore Wind Farm Project that was submitted to DTI in October 2005 The decommissioning programme addresses all components of the wind farm below mean high water springs The onshore aspects of the project and the associated decommissioning requirements fall under the planning permission granted under Section 57 Town and Country Planning Act 1990 by Suffolk Coastal District Council
Whilst the design life for the wind turbines is 25 years the lease term for the project is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term Nonetheless GGOWL acknowledges the UKrsquos international obligations requiring installations to be decommissioned as soon as is reasonably practicable This programme therefore sets out the measures for decommissioning the project at the end of the design life of the equipment during year 25 It is expected that as this time approaches GGOWL will seek approval from the Secretary of State to delay the decommissioning work in favour of re-powering the project
The programme is to be reviewed and revised as necessary throughout the lifecycle of the project to reflect changing circumstances and regulatory requirements and to incorporate improvements in knowledge and understanding of the marine environment and advances in technology and working practices
20 EXECUTIVE SUMMARY
The Energy Act 2004 requires that GGOWL prepares and ultimately carries out a decommissioning programme for the Greater Gabbard Offshore Wind Farm This document
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constitutes the preliminary decommissioning programme for the project and is submitted for approval prior to the construction of the wind farm
The programme is informed and supported by the Environmental Impact Assessment (EIA) carried out for the Greater Gabbard Offshore Wind Farm Project The resulting Environmental Statement was submitted as part of the projectrsquos application for consent in October 2005 The Environmental Statement provides detailed analysis of the baseline physical biological and human environment The assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are consistent with those presented in this document A CD version of the Environmental Statement is provided as Annex A to this document
The programme is also informed by the outcome of the Appropriate Assessment undertaken prior to the consent of the wind farm This document is also provided as Annex B
In considering appropriate decommissioning provisions GGOWL have sought to adhere to the following key principles
bull Safety for all at all times
bull Consideration of the rights and needs of legitimate users of the sea
bull Minimise environmental impact
bull Promote sustainable development
bull Adhere to the Polluter Pays Principle
bull Maximise the reuse of materials
bull Commercial viability
bull Practical integrity
The following key documents have also informed the provisions presented
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
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bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
GGOWLrsquos starting assumption for establishing the extent of decommissioning is complete removal This assumption has been assessed against the guiding principles listed above and where appropriate alternative solutions have been identified A summary of the proposals for decommissioning the offshore components of the Greater Gabbard Offshore Wind Farm are outlined in the table below
Component Decommissioning Proposal
Wind Turbinegenerating equipment Complete removal from site
Foundations (wind turbine met mast transformer platforms) Cut off at or below seabed and removed
Cables (inter-array and export) Left in situ
Anemometry masts Complete removal of structure
Transformer platforms Complete removal of topside
The measures proposed to decommission the installations as described above reflect the strong emphasis GGOWL puts on minimising risks to safety and to the environment As such GGOWL has sought practical solutions that involve minimal offshore operations
In the absence of re-powering GGOWL intends to begin decommissioning the project at year 25 It is intended that this process offshore be completed over a period of 300 days
The decommissioning programme as currently proposed is to be reviewed and revised throughout the lifecycle of the project to reflect changing circumstances and regulatory requirements and to incorporate improvements in knowledge and understanding of the marine environment and advances in technology and working practices A formal schedule for review is proposed where year 23 is identified as the final opportunity for a thorough review and consultation process
GGOWLrsquos approach to consultation about these works mirrors that undertaken during the EIA process for the project where importance is attached to early and open communication
Page 6 of 58
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with all key stakeholders Key stakeholders will have the opportunity to input into the draft decommissioning programme and to consider the final programme to be agreed prior to decommissioning Appropriate consultation and notification will be undertaken prior to the works taking place
A cost estimate for the programme has been derived based on the equipment and personnel requirements and the duration of the works Financial security provisions have been carefully considered to ensure that this liability will be met Details of the cost and financial aspects of the proposals are provided as Annex C to this programme
30 BACKGROUND INFORMATION
31 Project Status
The Greater Gabbard Offshore Wind Farm was awarded through the Round Two site allocation process in December 2003
An Environmental Impact Assessment was carried out and an application for consent for the project submitted in October 2005 The project was awarded the following consents in February 2007
bull Section 36 Electricity Act 1989 (construction and operation of the wind turbines offshore transformer stations and met masts granted by DTI)
bull Section 5 Food and Environment Protection Act 1985 (installation of foundations of offshore structures rock armouring scour protection etc granted by DEFRA)
bull Section 34 Coast Protection Act 1949 (obstruction to navigation works granted by DEFRA)
bull Section 36A Electricity Act 1989 (navigation extinguishment declaration granted by DTI)
Planning permission has also been received under Section 57 of the Town and Country Planning Act 1990 for the onshore works at Sizewell
The project is scheduled to commence construction offshore in late 2008
32 Project Overview
The wind farm is to be located 26km off the Suffolk coast adjacent to two sand banks known as Inner Gabbard and The Galloper The project comprises 140 wind turbines which will be installed over a total area of 147km2 and will generate a maximum capacity of 500MW The power will be brought to shore at Sizewell where an onshore sub-station will be located to connect the wind farm to the National Grid Figure 1 below shows the sitersquos location boundaries and the cable route to shore
Page 7 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 1 Greater Gabbard Site Boundaries
The site coordinates are as follows
Page 8 of 58
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Offshore transformer platforms will transform the turbine interconnection voltage from 33kV to 132kV for transmission ashore by up to four export cables These offshore sub-stations will have typical dimensions in the order of 20m length x 20m width x 15m height
Up to six permanent meteorological masts of a nominal height of up to 105m will also be constructed
The foundations for the wind turbines will be steel monopiles of up to 65m diameter driven into the seabed using a hydraulic hammer from a jack-up bargedrilling rig or purpose built installation vessel Scour protection in the form of rock gravel or frond mats may be used
Transition sections will be used to connect the wind turbine tower to the foundation by means of a grouted joint or a flanged connection
The foundations for the meteorological masts will consist of a steel monopile with a diameter of approximately 25m Scour protection may be required and would be similar to that used for wind turbine monopiles
The foundations for the offshore substations will be based on a jacket structure which will be secured to the seabed with piles
If required the use of scour protection around the foundations may consist of loose rock or rough gravel to be installed by means of grab and drop or bulldozed over the side of a vessel The use of mattresses for protection may also be used and installed by means of lowering from a vessel to the base of the foundation
The turbines will be connected to the offshore sub-stations via a network of 33kV cables (inter-array cables) that are laid between the wind turbines and the offshore sub-stations Up to four subsea 132kV cables (export cables) will connect the wind farm to the shore
The inter-array and export cables are likely to be buried using an underwater cable plough that executes a simultaneous lay and burial technique by lifting a wedge of sediment allowing the cable to fall into this trench and then folding the sediment back on top of the cable In exceptional circumstances and only following written authorisation from DEFRA cable burial Remote Operated Vehicle (ROV) may be used This utilises high-pressure water jets to fluidise a narrow trench into which the cable is located The jetted sediments settle back into the trench
The inter-tidal cables may be installed from a barge or jack-up which is either beached or moored near Sizewell beach The cable will be pulled beneath the inter-tidal zone using a directional drilling technique either beginning at the start of the run out to sea or at the end of the run from sea Near shore and deep water lay may be separate operations
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33 Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm The final layout will be determined in agreement with DTI prior to construction
Page 10 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
Page 11 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
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Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
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Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
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Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
Page 30 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
Page 31 of 58
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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10 INTRODUCTION
The Greater Gabbard Offshore Wind Farm will feature 140 turbines generating a total capacity of 500MW Covering approximately 147km2 the project will be located some 26km off the Suffolk coast adjacent to sandbanks known as Inner Gabbard and The Galloper
The wind farm is being developed by Greater Gabbard Offshore Winds Limited (GGOWL) a company formed specifically to develop finance construct operate and decommission the project The company is jointly owned by Airtricity Holdings (UK) Limited and Fluor International Limited
GGOWL obtained consent under Section 36 of the Electricity Act 1989 in February 2007 for the Greater Gabbard Offshore Wind Farm At this time the DTI also issued GGOWL a notice under Section 105(2) of the Energy Act 2004 regarding the requirement to prepare and obtain approval for the decommissioning programme for the project prior to construction commencement
This document presents the decommissioning programme for the Greater Gabbard Offshore Wind Farm and is being submitted for approval in accordance with the Energy Act 2004 requirements The decommissioning programme is informed and supported by the Environmental Impact Assessment (EIA) for the Greater Gabbard Offshore Wind Farm Project that was submitted to DTI in October 2005 The decommissioning programme addresses all components of the wind farm below mean high water springs The onshore aspects of the project and the associated decommissioning requirements fall under the planning permission granted under Section 57 Town and Country Planning Act 1990 by Suffolk Coastal District Council
Whilst the design life for the wind turbines is 25 years the lease term for the project is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term Nonetheless GGOWL acknowledges the UKrsquos international obligations requiring installations to be decommissioned as soon as is reasonably practicable This programme therefore sets out the measures for decommissioning the project at the end of the design life of the equipment during year 25 It is expected that as this time approaches GGOWL will seek approval from the Secretary of State to delay the decommissioning work in favour of re-powering the project
The programme is to be reviewed and revised as necessary throughout the lifecycle of the project to reflect changing circumstances and regulatory requirements and to incorporate improvements in knowledge and understanding of the marine environment and advances in technology and working practices
20 EXECUTIVE SUMMARY
The Energy Act 2004 requires that GGOWL prepares and ultimately carries out a decommissioning programme for the Greater Gabbard Offshore Wind Farm This document
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constitutes the preliminary decommissioning programme for the project and is submitted for approval prior to the construction of the wind farm
The programme is informed and supported by the Environmental Impact Assessment (EIA) carried out for the Greater Gabbard Offshore Wind Farm Project The resulting Environmental Statement was submitted as part of the projectrsquos application for consent in October 2005 The Environmental Statement provides detailed analysis of the baseline physical biological and human environment The assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are consistent with those presented in this document A CD version of the Environmental Statement is provided as Annex A to this document
The programme is also informed by the outcome of the Appropriate Assessment undertaken prior to the consent of the wind farm This document is also provided as Annex B
In considering appropriate decommissioning provisions GGOWL have sought to adhere to the following key principles
bull Safety for all at all times
bull Consideration of the rights and needs of legitimate users of the sea
bull Minimise environmental impact
bull Promote sustainable development
bull Adhere to the Polluter Pays Principle
bull Maximise the reuse of materials
bull Commercial viability
bull Practical integrity
The following key documents have also informed the provisions presented
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
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bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
GGOWLrsquos starting assumption for establishing the extent of decommissioning is complete removal This assumption has been assessed against the guiding principles listed above and where appropriate alternative solutions have been identified A summary of the proposals for decommissioning the offshore components of the Greater Gabbard Offshore Wind Farm are outlined in the table below
Component Decommissioning Proposal
Wind Turbinegenerating equipment Complete removal from site
Foundations (wind turbine met mast transformer platforms) Cut off at or below seabed and removed
Cables (inter-array and export) Left in situ
Anemometry masts Complete removal of structure
Transformer platforms Complete removal of topside
The measures proposed to decommission the installations as described above reflect the strong emphasis GGOWL puts on minimising risks to safety and to the environment As such GGOWL has sought practical solutions that involve minimal offshore operations
In the absence of re-powering GGOWL intends to begin decommissioning the project at year 25 It is intended that this process offshore be completed over a period of 300 days
The decommissioning programme as currently proposed is to be reviewed and revised throughout the lifecycle of the project to reflect changing circumstances and regulatory requirements and to incorporate improvements in knowledge and understanding of the marine environment and advances in technology and working practices A formal schedule for review is proposed where year 23 is identified as the final opportunity for a thorough review and consultation process
GGOWLrsquos approach to consultation about these works mirrors that undertaken during the EIA process for the project where importance is attached to early and open communication
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with all key stakeholders Key stakeholders will have the opportunity to input into the draft decommissioning programme and to consider the final programme to be agreed prior to decommissioning Appropriate consultation and notification will be undertaken prior to the works taking place
A cost estimate for the programme has been derived based on the equipment and personnel requirements and the duration of the works Financial security provisions have been carefully considered to ensure that this liability will be met Details of the cost and financial aspects of the proposals are provided as Annex C to this programme
30 BACKGROUND INFORMATION
31 Project Status
The Greater Gabbard Offshore Wind Farm was awarded through the Round Two site allocation process in December 2003
An Environmental Impact Assessment was carried out and an application for consent for the project submitted in October 2005 The project was awarded the following consents in February 2007
bull Section 36 Electricity Act 1989 (construction and operation of the wind turbines offshore transformer stations and met masts granted by DTI)
bull Section 5 Food and Environment Protection Act 1985 (installation of foundations of offshore structures rock armouring scour protection etc granted by DEFRA)
bull Section 34 Coast Protection Act 1949 (obstruction to navigation works granted by DEFRA)
bull Section 36A Electricity Act 1989 (navigation extinguishment declaration granted by DTI)
Planning permission has also been received under Section 57 of the Town and Country Planning Act 1990 for the onshore works at Sizewell
The project is scheduled to commence construction offshore in late 2008
32 Project Overview
The wind farm is to be located 26km off the Suffolk coast adjacent to two sand banks known as Inner Gabbard and The Galloper The project comprises 140 wind turbines which will be installed over a total area of 147km2 and will generate a maximum capacity of 500MW The power will be brought to shore at Sizewell where an onshore sub-station will be located to connect the wind farm to the National Grid Figure 1 below shows the sitersquos location boundaries and the cable route to shore
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Figure 1 Greater Gabbard Site Boundaries
The site coordinates are as follows
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Offshore transformer platforms will transform the turbine interconnection voltage from 33kV to 132kV for transmission ashore by up to four export cables These offshore sub-stations will have typical dimensions in the order of 20m length x 20m width x 15m height
Up to six permanent meteorological masts of a nominal height of up to 105m will also be constructed
The foundations for the wind turbines will be steel monopiles of up to 65m diameter driven into the seabed using a hydraulic hammer from a jack-up bargedrilling rig or purpose built installation vessel Scour protection in the form of rock gravel or frond mats may be used
Transition sections will be used to connect the wind turbine tower to the foundation by means of a grouted joint or a flanged connection
The foundations for the meteorological masts will consist of a steel monopile with a diameter of approximately 25m Scour protection may be required and would be similar to that used for wind turbine monopiles
The foundations for the offshore substations will be based on a jacket structure which will be secured to the seabed with piles
If required the use of scour protection around the foundations may consist of loose rock or rough gravel to be installed by means of grab and drop or bulldozed over the side of a vessel The use of mattresses for protection may also be used and installed by means of lowering from a vessel to the base of the foundation
The turbines will be connected to the offshore sub-stations via a network of 33kV cables (inter-array cables) that are laid between the wind turbines and the offshore sub-stations Up to four subsea 132kV cables (export cables) will connect the wind farm to the shore
The inter-array and export cables are likely to be buried using an underwater cable plough that executes a simultaneous lay and burial technique by lifting a wedge of sediment allowing the cable to fall into this trench and then folding the sediment back on top of the cable In exceptional circumstances and only following written authorisation from DEFRA cable burial Remote Operated Vehicle (ROV) may be used This utilises high-pressure water jets to fluidise a narrow trench into which the cable is located The jetted sediments settle back into the trench
The inter-tidal cables may be installed from a barge or jack-up which is either beached or moored near Sizewell beach The cable will be pulled beneath the inter-tidal zone using a directional drilling technique either beginning at the start of the run out to sea or at the end of the run from sea Near shore and deep water lay may be separate operations
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33 Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm The final layout will be determined in agreement with DTI prior to construction
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Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
Page 11 of 58
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bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
Page 34 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
Page 35 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
Page 36 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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constitutes the preliminary decommissioning programme for the project and is submitted for approval prior to the construction of the wind farm
The programme is informed and supported by the Environmental Impact Assessment (EIA) carried out for the Greater Gabbard Offshore Wind Farm Project The resulting Environmental Statement was submitted as part of the projectrsquos application for consent in October 2005 The Environmental Statement provides detailed analysis of the baseline physical biological and human environment The assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are consistent with those presented in this document A CD version of the Environmental Statement is provided as Annex A to this document
The programme is also informed by the outcome of the Appropriate Assessment undertaken prior to the consent of the wind farm This document is also provided as Annex B
In considering appropriate decommissioning provisions GGOWL have sought to adhere to the following key principles
bull Safety for all at all times
bull Consideration of the rights and needs of legitimate users of the sea
bull Minimise environmental impact
bull Promote sustainable development
bull Adhere to the Polluter Pays Principle
bull Maximise the reuse of materials
bull Commercial viability
bull Practical integrity
The following key documents have also informed the provisions presented
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
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bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
GGOWLrsquos starting assumption for establishing the extent of decommissioning is complete removal This assumption has been assessed against the guiding principles listed above and where appropriate alternative solutions have been identified A summary of the proposals for decommissioning the offshore components of the Greater Gabbard Offshore Wind Farm are outlined in the table below
Component Decommissioning Proposal
Wind Turbinegenerating equipment Complete removal from site
Foundations (wind turbine met mast transformer platforms) Cut off at or below seabed and removed
Cables (inter-array and export) Left in situ
Anemometry masts Complete removal of structure
Transformer platforms Complete removal of topside
The measures proposed to decommission the installations as described above reflect the strong emphasis GGOWL puts on minimising risks to safety and to the environment As such GGOWL has sought practical solutions that involve minimal offshore operations
In the absence of re-powering GGOWL intends to begin decommissioning the project at year 25 It is intended that this process offshore be completed over a period of 300 days
The decommissioning programme as currently proposed is to be reviewed and revised throughout the lifecycle of the project to reflect changing circumstances and regulatory requirements and to incorporate improvements in knowledge and understanding of the marine environment and advances in technology and working practices A formal schedule for review is proposed where year 23 is identified as the final opportunity for a thorough review and consultation process
GGOWLrsquos approach to consultation about these works mirrors that undertaken during the EIA process for the project where importance is attached to early and open communication
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with all key stakeholders Key stakeholders will have the opportunity to input into the draft decommissioning programme and to consider the final programme to be agreed prior to decommissioning Appropriate consultation and notification will be undertaken prior to the works taking place
A cost estimate for the programme has been derived based on the equipment and personnel requirements and the duration of the works Financial security provisions have been carefully considered to ensure that this liability will be met Details of the cost and financial aspects of the proposals are provided as Annex C to this programme
30 BACKGROUND INFORMATION
31 Project Status
The Greater Gabbard Offshore Wind Farm was awarded through the Round Two site allocation process in December 2003
An Environmental Impact Assessment was carried out and an application for consent for the project submitted in October 2005 The project was awarded the following consents in February 2007
bull Section 36 Electricity Act 1989 (construction and operation of the wind turbines offshore transformer stations and met masts granted by DTI)
bull Section 5 Food and Environment Protection Act 1985 (installation of foundations of offshore structures rock armouring scour protection etc granted by DEFRA)
bull Section 34 Coast Protection Act 1949 (obstruction to navigation works granted by DEFRA)
bull Section 36A Electricity Act 1989 (navigation extinguishment declaration granted by DTI)
Planning permission has also been received under Section 57 of the Town and Country Planning Act 1990 for the onshore works at Sizewell
The project is scheduled to commence construction offshore in late 2008
32 Project Overview
The wind farm is to be located 26km off the Suffolk coast adjacent to two sand banks known as Inner Gabbard and The Galloper The project comprises 140 wind turbines which will be installed over a total area of 147km2 and will generate a maximum capacity of 500MW The power will be brought to shore at Sizewell where an onshore sub-station will be located to connect the wind farm to the National Grid Figure 1 below shows the sitersquos location boundaries and the cable route to shore
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Figure 1 Greater Gabbard Site Boundaries
The site coordinates are as follows
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Offshore transformer platforms will transform the turbine interconnection voltage from 33kV to 132kV for transmission ashore by up to four export cables These offshore sub-stations will have typical dimensions in the order of 20m length x 20m width x 15m height
Up to six permanent meteorological masts of a nominal height of up to 105m will also be constructed
The foundations for the wind turbines will be steel monopiles of up to 65m diameter driven into the seabed using a hydraulic hammer from a jack-up bargedrilling rig or purpose built installation vessel Scour protection in the form of rock gravel or frond mats may be used
Transition sections will be used to connect the wind turbine tower to the foundation by means of a grouted joint or a flanged connection
The foundations for the meteorological masts will consist of a steel monopile with a diameter of approximately 25m Scour protection may be required and would be similar to that used for wind turbine monopiles
The foundations for the offshore substations will be based on a jacket structure which will be secured to the seabed with piles
If required the use of scour protection around the foundations may consist of loose rock or rough gravel to be installed by means of grab and drop or bulldozed over the side of a vessel The use of mattresses for protection may also be used and installed by means of lowering from a vessel to the base of the foundation
The turbines will be connected to the offshore sub-stations via a network of 33kV cables (inter-array cables) that are laid between the wind turbines and the offshore sub-stations Up to four subsea 132kV cables (export cables) will connect the wind farm to the shore
The inter-array and export cables are likely to be buried using an underwater cable plough that executes a simultaneous lay and burial technique by lifting a wedge of sediment allowing the cable to fall into this trench and then folding the sediment back on top of the cable In exceptional circumstances and only following written authorisation from DEFRA cable burial Remote Operated Vehicle (ROV) may be used This utilises high-pressure water jets to fluidise a narrow trench into which the cable is located The jetted sediments settle back into the trench
The inter-tidal cables may be installed from a barge or jack-up which is either beached or moored near Sizewell beach The cable will be pulled beneath the inter-tidal zone using a directional drilling technique either beginning at the start of the run out to sea or at the end of the run from sea Near shore and deep water lay may be separate operations
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33 Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm The final layout will be determined in agreement with DTI prior to construction
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Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
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bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
Page 19 of 58
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Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
Page 20 of 58
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Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
Page 26 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
Page 43 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
Page 45 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
GGOWLrsquos starting assumption for establishing the extent of decommissioning is complete removal This assumption has been assessed against the guiding principles listed above and where appropriate alternative solutions have been identified A summary of the proposals for decommissioning the offshore components of the Greater Gabbard Offshore Wind Farm are outlined in the table below
Component Decommissioning Proposal
Wind Turbinegenerating equipment Complete removal from site
Foundations (wind turbine met mast transformer platforms) Cut off at or below seabed and removed
Cables (inter-array and export) Left in situ
Anemometry masts Complete removal of structure
Transformer platforms Complete removal of topside
The measures proposed to decommission the installations as described above reflect the strong emphasis GGOWL puts on minimising risks to safety and to the environment As such GGOWL has sought practical solutions that involve minimal offshore operations
In the absence of re-powering GGOWL intends to begin decommissioning the project at year 25 It is intended that this process offshore be completed over a period of 300 days
The decommissioning programme as currently proposed is to be reviewed and revised throughout the lifecycle of the project to reflect changing circumstances and regulatory requirements and to incorporate improvements in knowledge and understanding of the marine environment and advances in technology and working practices A formal schedule for review is proposed where year 23 is identified as the final opportunity for a thorough review and consultation process
GGOWLrsquos approach to consultation about these works mirrors that undertaken during the EIA process for the project where importance is attached to early and open communication
Page 6 of 58
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with all key stakeholders Key stakeholders will have the opportunity to input into the draft decommissioning programme and to consider the final programme to be agreed prior to decommissioning Appropriate consultation and notification will be undertaken prior to the works taking place
A cost estimate for the programme has been derived based on the equipment and personnel requirements and the duration of the works Financial security provisions have been carefully considered to ensure that this liability will be met Details of the cost and financial aspects of the proposals are provided as Annex C to this programme
30 BACKGROUND INFORMATION
31 Project Status
The Greater Gabbard Offshore Wind Farm was awarded through the Round Two site allocation process in December 2003
An Environmental Impact Assessment was carried out and an application for consent for the project submitted in October 2005 The project was awarded the following consents in February 2007
bull Section 36 Electricity Act 1989 (construction and operation of the wind turbines offshore transformer stations and met masts granted by DTI)
bull Section 5 Food and Environment Protection Act 1985 (installation of foundations of offshore structures rock armouring scour protection etc granted by DEFRA)
bull Section 34 Coast Protection Act 1949 (obstruction to navigation works granted by DEFRA)
bull Section 36A Electricity Act 1989 (navigation extinguishment declaration granted by DTI)
Planning permission has also been received under Section 57 of the Town and Country Planning Act 1990 for the onshore works at Sizewell
The project is scheduled to commence construction offshore in late 2008
32 Project Overview
The wind farm is to be located 26km off the Suffolk coast adjacent to two sand banks known as Inner Gabbard and The Galloper The project comprises 140 wind turbines which will be installed over a total area of 147km2 and will generate a maximum capacity of 500MW The power will be brought to shore at Sizewell where an onshore sub-station will be located to connect the wind farm to the National Grid Figure 1 below shows the sitersquos location boundaries and the cable route to shore
Page 7 of 58
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Figure 1 Greater Gabbard Site Boundaries
The site coordinates are as follows
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Offshore transformer platforms will transform the turbine interconnection voltage from 33kV to 132kV for transmission ashore by up to four export cables These offshore sub-stations will have typical dimensions in the order of 20m length x 20m width x 15m height
Up to six permanent meteorological masts of a nominal height of up to 105m will also be constructed
The foundations for the wind turbines will be steel monopiles of up to 65m diameter driven into the seabed using a hydraulic hammer from a jack-up bargedrilling rig or purpose built installation vessel Scour protection in the form of rock gravel or frond mats may be used
Transition sections will be used to connect the wind turbine tower to the foundation by means of a grouted joint or a flanged connection
The foundations for the meteorological masts will consist of a steel monopile with a diameter of approximately 25m Scour protection may be required and would be similar to that used for wind turbine monopiles
The foundations for the offshore substations will be based on a jacket structure which will be secured to the seabed with piles
If required the use of scour protection around the foundations may consist of loose rock or rough gravel to be installed by means of grab and drop or bulldozed over the side of a vessel The use of mattresses for protection may also be used and installed by means of lowering from a vessel to the base of the foundation
The turbines will be connected to the offshore sub-stations via a network of 33kV cables (inter-array cables) that are laid between the wind turbines and the offshore sub-stations Up to four subsea 132kV cables (export cables) will connect the wind farm to the shore
The inter-array and export cables are likely to be buried using an underwater cable plough that executes a simultaneous lay and burial technique by lifting a wedge of sediment allowing the cable to fall into this trench and then folding the sediment back on top of the cable In exceptional circumstances and only following written authorisation from DEFRA cable burial Remote Operated Vehicle (ROV) may be used This utilises high-pressure water jets to fluidise a narrow trench into which the cable is located The jetted sediments settle back into the trench
The inter-tidal cables may be installed from a barge or jack-up which is either beached or moored near Sizewell beach The cable will be pulled beneath the inter-tidal zone using a directional drilling technique either beginning at the start of the run out to sea or at the end of the run from sea Near shore and deep water lay may be separate operations
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33 Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm The final layout will be determined in agreement with DTI prior to construction
Page 10 of 58
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Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
Page 11 of 58
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bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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with all key stakeholders Key stakeholders will have the opportunity to input into the draft decommissioning programme and to consider the final programme to be agreed prior to decommissioning Appropriate consultation and notification will be undertaken prior to the works taking place
A cost estimate for the programme has been derived based on the equipment and personnel requirements and the duration of the works Financial security provisions have been carefully considered to ensure that this liability will be met Details of the cost and financial aspects of the proposals are provided as Annex C to this programme
30 BACKGROUND INFORMATION
31 Project Status
The Greater Gabbard Offshore Wind Farm was awarded through the Round Two site allocation process in December 2003
An Environmental Impact Assessment was carried out and an application for consent for the project submitted in October 2005 The project was awarded the following consents in February 2007
bull Section 36 Electricity Act 1989 (construction and operation of the wind turbines offshore transformer stations and met masts granted by DTI)
bull Section 5 Food and Environment Protection Act 1985 (installation of foundations of offshore structures rock armouring scour protection etc granted by DEFRA)
bull Section 34 Coast Protection Act 1949 (obstruction to navigation works granted by DEFRA)
bull Section 36A Electricity Act 1989 (navigation extinguishment declaration granted by DTI)
Planning permission has also been received under Section 57 of the Town and Country Planning Act 1990 for the onshore works at Sizewell
The project is scheduled to commence construction offshore in late 2008
32 Project Overview
The wind farm is to be located 26km off the Suffolk coast adjacent to two sand banks known as Inner Gabbard and The Galloper The project comprises 140 wind turbines which will be installed over a total area of 147km2 and will generate a maximum capacity of 500MW The power will be brought to shore at Sizewell where an onshore sub-station will be located to connect the wind farm to the National Grid Figure 1 below shows the sitersquos location boundaries and the cable route to shore
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Figure 1 Greater Gabbard Site Boundaries
The site coordinates are as follows
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Offshore transformer platforms will transform the turbine interconnection voltage from 33kV to 132kV for transmission ashore by up to four export cables These offshore sub-stations will have typical dimensions in the order of 20m length x 20m width x 15m height
Up to six permanent meteorological masts of a nominal height of up to 105m will also be constructed
The foundations for the wind turbines will be steel monopiles of up to 65m diameter driven into the seabed using a hydraulic hammer from a jack-up bargedrilling rig or purpose built installation vessel Scour protection in the form of rock gravel or frond mats may be used
Transition sections will be used to connect the wind turbine tower to the foundation by means of a grouted joint or a flanged connection
The foundations for the meteorological masts will consist of a steel monopile with a diameter of approximately 25m Scour protection may be required and would be similar to that used for wind turbine monopiles
The foundations for the offshore substations will be based on a jacket structure which will be secured to the seabed with piles
If required the use of scour protection around the foundations may consist of loose rock or rough gravel to be installed by means of grab and drop or bulldozed over the side of a vessel The use of mattresses for protection may also be used and installed by means of lowering from a vessel to the base of the foundation
The turbines will be connected to the offshore sub-stations via a network of 33kV cables (inter-array cables) that are laid between the wind turbines and the offshore sub-stations Up to four subsea 132kV cables (export cables) will connect the wind farm to the shore
The inter-array and export cables are likely to be buried using an underwater cable plough that executes a simultaneous lay and burial technique by lifting a wedge of sediment allowing the cable to fall into this trench and then folding the sediment back on top of the cable In exceptional circumstances and only following written authorisation from DEFRA cable burial Remote Operated Vehicle (ROV) may be used This utilises high-pressure water jets to fluidise a narrow trench into which the cable is located The jetted sediments settle back into the trench
The inter-tidal cables may be installed from a barge or jack-up which is either beached or moored near Sizewell beach The cable will be pulled beneath the inter-tidal zone using a directional drilling technique either beginning at the start of the run out to sea or at the end of the run from sea Near shore and deep water lay may be separate operations
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33 Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm The final layout will be determined in agreement with DTI prior to construction
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Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
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bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
Page 19 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
Page 20 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 1 Greater Gabbard Site Boundaries
The site coordinates are as follows
Page 8 of 58
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Offshore transformer platforms will transform the turbine interconnection voltage from 33kV to 132kV for transmission ashore by up to four export cables These offshore sub-stations will have typical dimensions in the order of 20m length x 20m width x 15m height
Up to six permanent meteorological masts of a nominal height of up to 105m will also be constructed
The foundations for the wind turbines will be steel monopiles of up to 65m diameter driven into the seabed using a hydraulic hammer from a jack-up bargedrilling rig or purpose built installation vessel Scour protection in the form of rock gravel or frond mats may be used
Transition sections will be used to connect the wind turbine tower to the foundation by means of a grouted joint or a flanged connection
The foundations for the meteorological masts will consist of a steel monopile with a diameter of approximately 25m Scour protection may be required and would be similar to that used for wind turbine monopiles
The foundations for the offshore substations will be based on a jacket structure which will be secured to the seabed with piles
If required the use of scour protection around the foundations may consist of loose rock or rough gravel to be installed by means of grab and drop or bulldozed over the side of a vessel The use of mattresses for protection may also be used and installed by means of lowering from a vessel to the base of the foundation
The turbines will be connected to the offshore sub-stations via a network of 33kV cables (inter-array cables) that are laid between the wind turbines and the offshore sub-stations Up to four subsea 132kV cables (export cables) will connect the wind farm to the shore
The inter-array and export cables are likely to be buried using an underwater cable plough that executes a simultaneous lay and burial technique by lifting a wedge of sediment allowing the cable to fall into this trench and then folding the sediment back on top of the cable In exceptional circumstances and only following written authorisation from DEFRA cable burial Remote Operated Vehicle (ROV) may be used This utilises high-pressure water jets to fluidise a narrow trench into which the cable is located The jetted sediments settle back into the trench
The inter-tidal cables may be installed from a barge or jack-up which is either beached or moored near Sizewell beach The cable will be pulled beneath the inter-tidal zone using a directional drilling technique either beginning at the start of the run out to sea or at the end of the run from sea Near shore and deep water lay may be separate operations
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33 Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm The final layout will be determined in agreement with DTI prior to construction
Page 10 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
Page 11 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Offshore transformer platforms will transform the turbine interconnection voltage from 33kV to 132kV for transmission ashore by up to four export cables These offshore sub-stations will have typical dimensions in the order of 20m length x 20m width x 15m height
Up to six permanent meteorological masts of a nominal height of up to 105m will also be constructed
The foundations for the wind turbines will be steel monopiles of up to 65m diameter driven into the seabed using a hydraulic hammer from a jack-up bargedrilling rig or purpose built installation vessel Scour protection in the form of rock gravel or frond mats may be used
Transition sections will be used to connect the wind turbine tower to the foundation by means of a grouted joint or a flanged connection
The foundations for the meteorological masts will consist of a steel monopile with a diameter of approximately 25m Scour protection may be required and would be similar to that used for wind turbine monopiles
The foundations for the offshore substations will be based on a jacket structure which will be secured to the seabed with piles
If required the use of scour protection around the foundations may consist of loose rock or rough gravel to be installed by means of grab and drop or bulldozed over the side of a vessel The use of mattresses for protection may also be used and installed by means of lowering from a vessel to the base of the foundation
The turbines will be connected to the offshore sub-stations via a network of 33kV cables (inter-array cables) that are laid between the wind turbines and the offshore sub-stations Up to four subsea 132kV cables (export cables) will connect the wind farm to the shore
The inter-array and export cables are likely to be buried using an underwater cable plough that executes a simultaneous lay and burial technique by lifting a wedge of sediment allowing the cable to fall into this trench and then folding the sediment back on top of the cable In exceptional circumstances and only following written authorisation from DEFRA cable burial Remote Operated Vehicle (ROV) may be used This utilises high-pressure water jets to fluidise a narrow trench into which the cable is located The jetted sediments settle back into the trench
The inter-tidal cables may be installed from a barge or jack-up which is either beached or moored near Sizewell beach The cable will be pulled beneath the inter-tidal zone using a directional drilling technique either beginning at the start of the run out to sea or at the end of the run from sea Near shore and deep water lay may be separate operations
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33 Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm The final layout will be determined in agreement with DTI prior to construction
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Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
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bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
Page 19 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
Page 20 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
Page 43 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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33 Layout of Wind Farm and Ancillary Works
Figure 2 shows an indicative layout of the wind farm The final layout will be determined in agreement with DTI prior to construction
Page 10 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
Page 11 of 58
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bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
Page 13 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
Page 14 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
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Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
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Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
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Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
Page 35 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Figure 2 Indicative Wind Farm Layout
34 Site Characteristics
341 Physical Characteristics
A range of surveys have been completed by GGOWL to establish the physical environment at the Greater Gabbard site These studies informed the Environmental Impact Assessment for the project and included
bull two geophysical surveys
bull a shallow geotechnical campaign (maximum penetration 25m)
bull a deeper geotechnical campaign (maximum penetration 50m)
bull a metocean campaign
bull benthic grab campaign
Additional information has also been obtained from other sources to complement that obtained from the above surveys described above The additional data acquisition includes
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bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
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Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
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Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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bull SeaZone sea bed bathymetry data to inform the far-field model domain and to provide base mapping
bull UK Hydrographic Office (UKHO) historical charts to inform the study of historical changes in the Inner Gabbard and The Galloper banks shape and form
bull Wavenet Data a strategic wave monitoring network that provides a single source of real time wave data from a network of wave buoys located offshore from areas at risk from flooding
bull TotalTide tidal level data to synthetically generate astronomical tidal level data and current speed so that measured data from the metocean surveys can be compared against the model data for an assessment of consistency
bull British Geological Survey (BGS) surface sediment information to provide a more regional indication of the sea bed material
bull Met Office data wind and wave time series to provide details on the longer-term offshore wave climate
The Greater Gabbard Environmental Statement (October 2005) presents a full description and analysis of the physical characteristics of the Greater Gabbard site Following the submission of the ES in October 2005 further detailed site investigation works have been carried out to further GGOWLs understanding of the site
The following sections provide summary information sufficient to inform consideration of the decommissioning provisions
A Metocean Characteristics
The location for the proposed Greater Gabbard Offshore Wind Farm (GGOWF) has the following metocean characteristics
Estimated Average Mean Wind 85-95 ms at 80m AMSL Speed (predicted) Water Depth Range -36m to ndash 8m CD (Inner Gabbard)
-24m to ndash 10m CD (The Galloper) -20m to ndash 50m (off the sandbanks)
Mean Surface Temperature 165degC (summer) 6degC (winter)
Salinity lt3475gkg (summer) gt3475gkg (winter)
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
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(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
Page 20 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
Page 33 of
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
Page 34 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
Page 35 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
Page 36 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
Page 38 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
Page 39 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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B Topographyamp Bathymetry
Regionally the bathymetry generally deepens gradually from the UK coastline to the central part of the Southern North Sea and shows a relatively flat surface predominantly between 20 and 40 metres water depth The area is characterised by large areas of low gradient upon which 5 linear ldquoopen-shelfrdquo sandbanks are formed These sandbanks include the Inner Gabbard and the Galloper Inner Gabbard and Galloper sandbanks are similar in shape and proportion
bull A width of 1 to 12km in the middle and shallowest section
bull A width of 14km to 15km at the northern and southern ends
bull A length of approximately 26km
Minimum depths on the Inner Gabbard and The Galloper are 38m and 25m CD respectively as surveyed in 2004 Both banks are thought to be relatively stable and are not expected to move significantly during the lifetime of the wind farm project
C Currents Tidal Streams and Rise and Fall of Tide
Tidal range varies across the area with a springneap range at Harwich of 3623 metres Storm surges due to abnormal weather conditions can cause significant changes to predicted heights with the sea rising up to 3 metres above these heights in extreme NW and N conditions or falling up to 2 metres below these heights in Southerly gales
General tidal flows are determined from the admiralty tidal stream atlas tide tables and the tidal diamonds on the chart At the Greater Gabbard site these tidal streams run at approximately 200 degrees from about 5 hours before HW Dover turning to approximately 020 degrees by 2 hours after HW Dover Tidal streams at the proposed site are noted as a maximum of 22 knots at spring tides
Astronomical tidal levels relevant to the Greater Gabbard site determined from the Admiralty tide tables for the nearby Standard Ports of Walton-on-the-Naze and Harwich are summarised below
Tidal Level (mCD)
LAT MLWS MLWN MHWN MHWS HAT
Walton-on-the-Naze
0 +040 +110 +340 +420 +460
Harwich 0 +040 +110 +340 +400 +440 Inner GabbardA +06 +09 +14 +31 +37 +40 GalloperB +02 +10 +13 +32 +38 +42
Page 13 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
Page 33 of
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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(A) Posn 51rsquo 56rdquo N 01rsquo 55rdquo E (B) Posn 51rsquo 48rdquo N 01rsquo 58rdquo E
Tidal streams running across the outer part of the Thames Estuary (due south of Orford Ness) are generally rectilinear running in a SSW (ingoing) or NNE (outgoing) direction Elsewhere tidal streams generally run in the direction of the coast
The tidal streams at The Galloper (51deg443rsquo N 1deg483rsquoE) are presented below
Time from High Water at Sheerness (hrs)
Current Direction Velocity (ms) Spring Tide Neap Tide
-6 320 01 01 -5 215 04 03 -4 209 07 05 -3 211 09 06 -2 216 08 05 -1 221 05 03 High Water 275 01 01 +1 029 04 03 +2 037 07 05 +3 039 09 06 +4 038 07 05 +5 036 05 03 +6 020 02 01
D Sea and Swell
From metocean surveys undertaken at the site the waves in the vicinity of the Inner Gabbard and The Galloper banks are all relatively small short period wind swells The local wind conditions appear to play an important role in determining the height and period of the waves in the region The area is also well known for storm surges and the extreme water levels in the area are caused by such surges acting over large tidal ranges
Metocean Surveys were undertaken in November 2004 and March 2005 to capture sufficient measures of waves water levels currents and suspended sediment concentrations within wind farm area The data provided was used to demonstrate an understanding of the waves and tides in the area and to allow a consideration of these processes in conjunction with sediment transport Understanding was also required for the occurrence and effects of major events in particular high frequency low energy events (tidally dominated events) and low frequency high energy events (wave dominated events) In general the surveys show that
bull Maximum tidal range is of the order of 4m
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
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Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
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Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Page 27 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
Page 48 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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bull surface currents peaked at approximately 18ms
bull bed currents were of the order of 07 to 17ms
bull the currents were aligned with the local sea bed topography
bull typical significant wave heights were of the order of 36m
bull maximum wave heights of the order of 62m were recorded
bull the larger waves tended to originate from the north-east
E Geological Characteristics
The solid geology at the site comprises a thick sequence of London Clay Formation of Eocene age comprising firm to stiff marine silty clay clayey and sandy silts and subordinate sands This formation is evident underneath the site and surrounding area to a depth of over 100m (this being the penetration of the geophysical survey) with outcrops at the seabed throughout the area Older Palaeocene strata (Lambeth Group and Thanet Formation) lie below the London Clay and above the surface of the Upper Chalk Neither these formations nor the chalk outcrop at the seabed within the site
There is evidence at the northern end of the Inner Gabbard of an east to west trending channel feature considered to be the Paleo-Stour which is interpreted as being filled with clayey sandy gravels and sandy gravelly clays
The Inner Gabbard and The Galloper are part of a group of very similar tidal sand banks that also includes the Outer Gabbard the North Falls and the South Falls These banks are of the open shelf linear type but they are particularly straight and narrow examples compared to other banks of this type
F Geophysical Surveys
Two geophysical survey campaigns were undertaken during 2004 and 2005 to provide detailed information on the bathymetry sea bed morphology obstructions and shallow geology
The first campaign showed that
bull The shallow geology is dominated by Holocene Sands overlying London Clay
bull The London Clay formation represents a sub-sea bed depth of between 60 and 100m
bull Water depths to either side of the banks reach 50m (CD)
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
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Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
Page 20 of 58
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Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
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Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
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Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
Page 33 of
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Page 42 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
Page 43 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
Page 45 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
Page 50 of 58
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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bull Sand waves occur on the sea bed to the south east of The Galloper
bull The remainder of the sea bed surrounding the banks is generally flat and featureless
bull Asymmetric sand waves occur on the flanks of both banks with the steeper sides in opposing directions on either side of the banks
bull Large sand wave covered by smaller sand waves and megaripples are shown on the southern end of Inner Gabbard
bull A pronounced paleo channel can be seen to the north of Inner Gabbard running east-west reaching depths of 37m (CD) and passes beneath the overlying sandbank
bull The minimum depths on the Inner Gabbard and The Galloper are 380m and 248m (CD) respectively
The second survey included areas that were added to the wind farm site following an agreed boundary change prior to the consent application This second survey campaign showed that within the main survey area
bull there are large areas of flat featureless seabed
bull zones of sand waves and mega ripples exist to the south and north
bull Holocene sediment (sands and gravels) overlay London Clay
bull the thickness of the Holocene material ranges from centimetres to 5m
bull the London Clay extends more than 100m below the sea bed
bull there is evidence of extensive faulting in sections of the London Clay
bull a paleo-channel exists to the north running east-west and is approximately 400 to 900m wide and up to 8m deep
In general the survey shows that along the cable route
bull the formations are generally the same as the main wind farm site
bull in the vicinity of Aldeburgh Napes the sea bed material is composed of medium to coarse grained sands
bull in the last 5km to the shore soft clays exist
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
Page 17 of 58
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
Page 18 of 58
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
Page 19 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
Page 20 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
Page 21 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
Page 43 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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G Geotechnical Surveys
A geotechnical survey was undertaken during September 2004 at four locations within the proposed Greater Gabbard Offshore Wind Farm site Two of the locations were on the Inner Gabbard and The Galloper sandbanks and two in the surrounding area The purpose of the survey was to acquire data relating to the underlying geology of the wind farm sites This was undertaken using a combination of sample boreholes Standard Penetration Tests (SPT) and Cone Penetrometer Test (CPT) at each location
In general the survey shows that
bull The sand layer is deeper on the banks than in the surrounding area The sandbanks have sediment depths of 1375m and 2165m on The Galloper and the Inner Gabbard respectively
bull In the surrounding area to The Galloper and the Inner Gabbard the depths of sand are 04m and 01m respectively
bull Sand found on the banks is essentially homogenous as slightly silty fine to medium sands Sand generally contains less than 2 of gravel size particles
bull Sand found in the surrounding areas has generally the same composition as on the banks but with a greater gravel size content (approximately 10) including shell fragments
bull The clay layer ranges from 1440m to 3565m deep
bull The clay is part of the lower London tertiary deposits known as London Clay
bull The clay is generally firm becoming stiff to very stiff with depth
bull Proportions of silt and clay are consistent typically about 45 and 55 respectively
A thorough geotechnical campaign was undertaken in 2006 This work confirmed the existing geotechnical knowledge
H Benthic Surveys
Detailed surveys were undertaken during November 2004 and April 2005 The surveys covered the proposed wind farm site and cable route The purpose was to acquire data relating to sediment characteristics and benthic communities particularly Sabellaria spinulosa In general the survey shows that
bull the Inner Gabbard and The Galloper sandbanks are composed of medium sands with some gravel content
Page 17 of 58
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bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
Page 18 of 58
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Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
Page 19 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
Page 20 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull the surrounding deeper sea bed is composed of differing sediment types characterised by mudclay sand and gravels in differing proportions
bull the cable route is characterised by a mix of sediments running through sands and gravels to muds and then sands from the Inner Gabbard to the shore respectively
35 Relevant Projects and Activities
There are presently a range of different developments and activities taking place in the vicinity of the Greater Gabbard Offshore Wind Farm GGOWL has undertaken extensive consultation with key stakeholders to inform the projectrsquos EIA A full analysis of the projects relevant to the Greater Gabbard project is contained in Section 8 of the Environmental Statement
It is proposed that the register of key consultees identified during the EIA process is reviewed and amended throughout the lifetime of the project and during the formal review opportunities identified in section 9 of this document Similarly a register of relevant activities and developments will be reviewed and maintained
A consultation strategy and schedule will be devised prior to decommissioning The nature of this strategy will reflect the activities underway at the time the interaction between these activities and the decommissioning works the relationships that have been built up with stakeholders and appropriate guidance and requirements that exist at the time In any event the strategy will be based on the principles of clear timely and open communication
The starting point for the development of this strategy is the identification of existing and reasonably foreseeable proposed developments in the region surrounding the Greater Gabbard offshore wind farm The following key activities currently take place in the area and a brief review is presented here
bull Other offshore wind farms
bull Marine aggregate extraction
bull Disposal of dredged material
bull Subsea cables
bull Oil and gas activities
It is noted that there are currently no oil and gas pipelines in the area
351 Offshore Wind Farms
A number of Round One and Round Two projects have been proposed or are in operation in the vicinity of the Greater Gabbard site
Page 18 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
Page 19 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
Page 20 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
Page 21 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Site Developer Round of
Award
Capacity Status Location Distance from
GGOW F
Kentish Flats
Vattenfall One 90MW Generating 85km off Whitstable
55km
Gunfleet DONG Energy One Up to Consented 8km off 40km Sands 108MW construction Clacton
due 2009 Gunfleet Sands II
DONG Energy Two 64MW Pre-consent 10km off Clacton
40km
London DONG Two Up to Consented 20km off 15km Array EnergyShellEON 1000MW Essex Thanet Warwick Energy Two 300MW Consented 13km off 35km
Margate
Page 19 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
Page 20 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
Page 21 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
Page 33 of
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
Page 43 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Figure 3 Offshore Wind Projects in the Greater Thames Estuary
It is possible that there may be synergies and interactions between decommissioning activities at the various sites GGOWL will promote formal industry collaboration on this issue and as a minimum will approach other developers to consider potential opportunities as part of the ongoing review process for the Greater Gabbard decommissioning programme However GGOWLrsquos starting assumption is that decommissioning will be undertaken in isolation at Greater Gabbard in order that the provisions can be fully costed and sufficient financial security provided The status and requirements of surrounding projects will be carefully considered in the planning and execution of the decommissioning process
352 Marine Aggregate Extraction
The following areas are licensed or are to be licensed (subject to consent) for the extraction of marine aggregate within 10 km of the wind farm site
Company Extraction Area Reference
Status Distance from Greater Gabbard
RMC marine (SCS) 2391 Licence 22km to NW RMC marine (SCS) 452 Application pending 05km to W
Page 20 of 58
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Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
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Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
Page 33 of
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
Page 43 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
Page 45 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Company Extraction Area Reference
Status Distance from Greater Gabbard
Hanson 1193 Licence 41km to W Figure 4 Marine Aggregate Areas in the vicinity of the Greater Gabbard Wind Farm
353 Disposal of Dredged Material
The majority of sites for the disposal of dredged material are at the mouth of estuaries and are primarily sized for the quantities of material excavated from rivers and ports The Thames Estuary has several established disposal areas
Name Status Distance from Greater Gabbard
Inner Gabbard Open 52km Area 1083 Open 173km Inner Gabbard (east) Submitted for
Consent 1km
North West Ship Wash (HU199)
Open 192km
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
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Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
Page 28 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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The proposed extension to the southern dock space in the Port of Felixstowe is currently under consideration The material extracted during the construction process (up to 386 Mm3) is proposed to be disposed at the existing Inner Gabbard dispersive disposal site and the site known as Inner Gabbard (east) disposal site
Figure 5 Marine Disposal Sites in the Vicinity of Greater Gabbard
354 Subsea Cables
There are eight known subsea cables in the vicinity of the project These are summarised in the following table (source The Crown Estate)
Company Reference Status Distance from Greater Gabbard
National Grid Transco
UK-Netherlands Interconnector (BritNed)
Consented South of turbine array
Hermes Hermes Telecoms cable not in operation
Intersects export cable route
GT UK Atlantic Crossing Seg B1
Telecoms cable in operation
3km to east of turbine array
BT Farlands Telecoms cable in operation
Intersects export cable route
Page 22 of 58
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Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
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Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Page 27 of 58
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
Page 29 of 58
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
Page 48 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Company Reference Status Distance from Greater Gabbard
BT UK Netherlands 4 Decommissioned NA BT UK Netherlands 12 Scheduled to be
decommissioned Intersects export cable route
Flute (interoute) Concerto North Telecoms cable in operation
Intersects export cable route
Flute (interoute) Concerto South Telecoms cable in operation
Intersects export cable route
Figure 6 Subsea Cables in the vicinity of Greater Gabbard
355 Oil and Gas
At the time of undertaking the Greater Gabbard offshore wind farm Environmental Impact Assessment there were no known offshore oil and gas activities within 10km of the proposed Greater Gabbard Offshore Wind Farm
During 2007 the 24th licensing round for oil and gas was announced A selection of the blocks awarded were within the Thames Estuary albeit some distance from the Greater Gabbard wind farm Figure 7 provides the details of those awards
Page 23 of 58
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Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
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bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
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Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
Page 30 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
Page 31 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
Page 33 of
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 7 Blocks Awarded in the Thames Estuary Region through the 24th Oil and Gas Licensing Round
356 Fishing Activity
Section 952 of the Environmental Statement provides a thorough analysis of the fishing activity on site and was informed by site surveys a review of existing data and consultation with industry
The type and volume of fishing activity currently taking place in the vicinity of Greater Gabbard offshore wind farm is relatively low Whilst the ground conditions at the site are reasonable for most types of fishing there are key constraints limiting activity including
Page 24 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
Page 25 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
Page 30 of 58
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
Page 33 of
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
Page 35 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
Page 36 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Lack of shelter The Inner Gabbard and The Galloper sandbanks provide little or no shelter to small vessels in any prevailing wind direction The sea becomes choppy above the sand banks making crossing and working the banks uncomfortable difficult and at times dangerous The sand banks themselves are generally described as ldquouncomfortablersquo by local fishermen
bull Weather conditions a major factor for many smaller vessels given the large distance between the site and shore
bull Wrecks there are a number of wrecks in the area of the sandbanks that are avoided by the drifters and trawlers
357 Shipping Activity
Section 953 of the Environmental Statement provides a thorough analysis of navigation activity in the vicinity of the Greater Gabbard offshore wind farm site and was informed by surveys a review of existing data and consultation with industry A review of this activity is presented below
Shipping using the area includes commercial shipping fishing recreational yachting and dredging The various sand banks in the area modulate the main routes for commercial traffic in the area with the lsquogapsrsquo between them being well marked east-west navigable channels that are used by vessels making their way into the main ship channels of the Thames and Haven ports
A Traffic Separation Scheme (TSS) and Vessel Traffic System (VTS) was proposed in August 2005 by the lsquoSunk User Grouprsquo A submission to United Kingdom Safety of Navigation (UKSON) was presented to the International Maritime Organisation (IMO) for adoption in 2007 This scheme has been approved and will be in place before the project is constructed
Maritime traffic Surveys conducted during 2004 indicated an average of 88 vessels per day in the area with an average number of 115 vessel tracks seen by radar per day Analysis shows that over 90 of these tracks were made by commercial shipping (cargo passenger tanker and dredger) with only 8 made by fishing vessels and 1 by recreational craft Most of the vessels were small with only 12 of the commercial vessels being over 40000 DWT The predominant flags of registry were UK and Dutch
The following Figure 8 shows information gathered on the busiest survey day 31st August 2004
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Figure 8 Shipping Traffic within the vicinity of Greater Gabbard Wind Farm 310804
36 Nature Conservation
There are no existing designations in the vicinity of the project that extend offshore although many parts of the coastline adjacent to the Greater Gabbard Offshore Wind Farm and landfall have some form of conservation status It is possible that the decommissioning process may impact the integrity of these sites The relevant and important designations along the coastline of Suffolk are as follows
Figure 9 Nature Conservation Designations in the Vicinity of Greater Gabbard
Page 26 of 58
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Page 27 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
Page 43 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
Page 45 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Ramsar Sites
Ramsar sites are wetlands of international importance and are designated under inter governmental treaty for their waterfowl populations their important plants and animal assemblages their wetland interest or a combination of these The convention allows for such sites to extend to 6m below mean low water The relevant sites are
Site Name Grid ref Area (ha)
Date Designated
Qualifying Interest
Minsmere-Walberswick (UK11044)
TM465662 2004 1976 extended 1992
Representative Wetland rare species
Alde-Ore Estuary (UK11002)
TM432487 2437 1996 Rare Species substantial numbers of individual waterfowl indicative of wetlands 1 of waterfowl species population
Special Areas of Conservation (SACs) and Special Protection Areas (SPAs)
SACs are covered by the Habitats Directive (Council Directive 9243EEC on the Conservation of Natural habitats and of Wild Fauna and Flora) which requires European member states to establish sites for the purpose of contributing to the maintenancerestoration of habitants and species of favourable conservation status listed in Annexes I and II of the Directive SACs relevant to the Greater Gabbard project are presented below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
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Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
Page 30 of 58
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
Page 31 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
Page 33 of
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Minsmere to Walberswick Heaths and Marshes (UK0012809)
TM468682 1265 2001 Annex I qualifying habitats are bull Annual vegetation of drift line bull European Dry Heaths
Alde Ore and Butley Estuaries SAC (UK0030076)
TM444509 1562 2001 Annex I qualifying habitats are bull Mudflats and sandflats not
covered by seawater at low tide bull Atlantic salt meadows
Orfordness ndash shingle Street SAC (UK0014780)
TM440486 901 2001 Annex I qualifying habitats are bull Coastal lagoons bull Annual vegetation of drift lines bull Perennial vegetation of stony
banks
SPAs are designated under the Birds Directive (Council Directive 79409EEC on the Conservation of wild birds) which requires member states to conserve habitats for rare or vulnerable species in addition to regularly occurring species of migratory birds In the UK all SPAs are first notified as SSSIs Relevant SPAs are detailed below
Site Name Grid Ref Area (ha)
Date Designated
Qualifying Interest
Minsmere - Walberswick (UK9009101)
TM465662 2000 1992 Nationally important numbers of six breeding species (Bittern Marsh Harrier Avocet Little Tern European Nightjar Wood Larks) and three wintering species (Bittern Hen Harrier Avocet)
Sandlings (UK9020286)
TM403602 1562 2001 Nationally important numbers of European Nightjar and Wood Larks
Alde Ore Estuary (UK9009112)
TM432487 2437 1996 Nationally important numbers of breeding Marsh Harrier Avocet Sandwich Tern and Little Tern and wintering Avocet internationally important numbers of wintering Redshank and breeding Lesser Black Backed Gull also important assemblages of breeding seabirds and wintering waterbirds
It is also possible that an SPA may be designated in the Greater Thames Estuary due to the presence of bird species including Red Throated Diver
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
Page 33 of
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
Page 35 of 58
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
An Appropriate Assessment was carried out prior to the Greater Gabbard Offshore Wind Farm receiving consent in order to satisfy the requirements of the Habitats Directive (EC9242EEC) and the Wild Birds Directive (EC79409EEC) known together as the Habitats Directive The Appropriate Assessment is provided as Annex B
This Assessment was considered necessary because of concerns raised about the potential impacts of the Greater Gabbard Offshore Wind Farm development on the breeding population of lesser black-backed gulls at the AldendashOre SPA and the potential cumulative impacts from the wind farm and other developments (proposed and extant) in the Thames Estuary on the integrity of the potential Greater Thames Estuary pSPA The Assessment addressed both these issues and taking into account impact predictions evidence from other sites uncertainties and whether there was reasonable cause for concern it found that the Greater Gabbard Offshore Wind Farm would not have an adverse effect on the integrity of the Alde-Ore SPA It was also found that at the present state of knowledge the wind farm would not have an adverse effect on the integrity of the Greater Thames Estuary pSPA either alone or in combination with other projects The Assessment took a lifecycle approach to the project with the conclusions applying to all phases of the works beyond construction and operation through to decommissioning
Sites of Special Scientific Interest
Sites of Special Scientific Interest (SSSI) are areas designated under the Wildlife and Countryside Act 1981 (Section 28) as being of national nature conservation interest They are intended to provide the best examples of wildlife habitats geological features and landforms and receive greater protection through the Countryside and Rights of Way Act 2000 There are a number of SSSIrsquos and an Area of Outstanding Natural Beauty (AONB) situated close to the export cable landfall and associated onshore works These are presented below
Site Name Grid Ref Area (ha) Date Designated Minsmere-Walberswick Heaths and Marshes TM465662 2326 1987 Sizewell Marshes TM466638 104 1992 Leiston-Aldeburgh TM461595 534 1986
Areas of Outstanding Natural Beauty
Site Name Area (ha) Date Designated Suffolk Coasts and Heaths 40400 1970
40 DESCRIPTION OF ITEMS TO BE DECOMMISSIONED
41 Guiding Principles
In considering the proposed decommissioning programme for the Greater Gabbard Offshore Wind Farm GGOWL has sought solutions that adhere to the following principles
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
Page 44 of 58
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Guiding Principle Comments
Safety for all at all times GGOWL is committed to adhering to the highest standards for health and safety throughout the lifecycle of the Greater Gabbard project GGOWL seek to promote safe practices and minimise risk in the development and implementation of decommissioning solutions
Consideration of the rights GGOWL respects the rights and needs of other users of the and needs legitimate users seabed Decommissioning activities will seek to minimise of the sea the impact on stakeholders and emphasis will be placed on
clear open communication Minimise environmental In considering decommissioning measures the Best impact Practicable Environmental Option (BPEO) will be chosen
in order to minimise impact on the environment at an acceptable cost
Promote sustainable In decommissioning the Greater Gabbard project GGOWL development will seek to ensure that as far as is reasonably practicable
future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
GGOWLrsquos decommissioning and waste management provisions acknowledge our responsibility to incur the costs associated with our impact on the environment
Maximise the reuse of materials
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo
Commercial Viability In order that commercial viability is maintained the BATNEEC (Best Available Technique not Entailing Excessive Cost) decommissioning solutions will be sought
Practical Integrity Solutions that are necessary to achieve one or more of the above objectives must be practicable
It is possible that not all of these objectives will be consistent with each other In such circumstances solutions will be optimised subject to the necessary constraints For example with respect to minimising the impact on the environment the Best Practicable Environmental Option (BPEO) will be sought where the option will be chosen that provides the most benefit or least damage to the environment as a whole at an acceptable cost in both the long and short term Similarly BATNEEC solutions ensure that the reduction in risk is balanced with the practicability and cost of doing so
In seeking to achieve these objectives GGOWL is also committed to adhering to UK legislation and international obligations As such GGOWL has drawn upon the following documents to ensure the decommissioning programme meets those requirements
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
Page 30 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
Page 35 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
Page 36 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull OSPAR guidance documents on offshore wind farms
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull United Nations Convention on the Law of the Sea (UNCLOS) 1982
Other legislation of relevance includes
bull Hazardous Waste Regulations 2005 and
bull London Convention 1972 and the 1996 Protocol relating to the prevention of marine pollution by dumping of wastes
bull Construction (Design and Management) Regulations 2007
bull Appropriate HampS Regulations
It is noted that archaeological no-build zones have been defined for the Greater Gabbard project Necessary measures will be put in place during the decommissioning of the project to ensure that these areas or other such areas that may be identified during the operation of the project are not compromised during decommissioning activities
42 Proposed Decommissioning
At the time of writing GGOWL is undertaking key design and development work for the project The overriding aim is to develop a project that is safe durable and cost-efficient throughout its lifetime Taking a lifecycle approach to the design and development work ensures that decommissioning considerations are incorporated into decision-making and where possible means that the principles identified above are being incorporated into early decision-making
Taking into account the UKrsquos commitments under UNCLOS IMO standards and the work of OSPAR GGOWLrsquos starting assumption in establishing the decommissioning requirements has been complete removal of all offshore components to shore for reuse recycling or incineration with energy recovery or disposal at a licensed site This assumption has been assessed for all components against the key criteria presented above In some instances this option has not been considered to be appropriate and alternative options have been
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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considered These alternatives have also been assessed according to the above criteria and the optimum solution selected
A further prerequisite for not fully removing a component is consistency with at least one of the circumstances set out on page 25 of DTI guidance as situations where such a solution may be considered These circumstances set out in the DTI guidance are listed below (it is noted that there is some duplication with the guiding principles described above)
bull ldquothe installation or structure will serve a new use whether for renewable energy generation or for another purpose such as enhancement of a living resource (provided it would not be detrimental to other aims such as conservation) In these situations we would normally expect the decommissioning programme to set out the eventual decommissioning measures envisaged should the installation or structure finally become lsquodisusedrsquo and a point reached when extending its life or finding a beneficial reuse is no longer possible
bull entire removal would involve extreme cost It is considered that design decisions should as far as possible result in installations which are affordable to remove but it is recognised that some elements such as deep foundations may nonetheless be costly to remove
bull entire removal would involve an unacceptable risk to personnel
bull entire removal would involve an unacceptable risk to the marine environment
bull the installation or structure weighs more than 4000 tonnes in air (excluding any deck and superstructure) or is standing in more than 100 m of water and could be left wholly or partially in place without causing unjustifiable interference with other uses of the seardquo
To facilitate assessment of the decommissioning proposals the analysis is preceded by a description of each of the components of the project to be decommissioned
421 Offshore Wind Turbines
Component Description
At the time of writing the make model and capacity of wind turbine to be installed at Greater Gabbard offshore wind farm has yet to be finalised These details will be confirmed prior to sign-off of the GGOWL decommissioning programme and the following provisions are based on the maximum dimensions and weights associated with a 36MW turbine and are consistent with the dimensions and weights used in GGOWLrsquos Environmental Statement
Consistent with the conditions of consent for the works the following decommissioning provisions assume a maximum tip height of 170m above Mean Sea Level (MSL) with a
Page 32 of 58
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
Page 36 of 58
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
Page 39 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Page 33 of
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
nominal 105m hub height and a maximum rotor diameter of 130m The towers will be tapered tubular steel towers
There will be three blades attached to a nacelle housing the generator gearbox and other operating equipment The unit transformer will be located in the tower base (above the high tide level)
The transformer will either be oil-filled (surrounded by a bund conforming to the required standards) or cast-resin
Figure 10 An Offshore Wind Turbine
The hub components of the offshore wind turbines will have a complete weight of 95 tonnes and will be made up of bull Hub casting nodular cast iron bull Blades three blades each up to 52m long and made from carbon fibre
Figures 11-13 Construction of an Offshore Wind Turbine
58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
Page 34 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The Nacelle will have dimensions in the order of 20m x 10m x 10m and will weigh approximately 125 tonnes Components will include
bull Gear box 50 tonnes bull Generator 50 tonnes bull Main Shaft and bearings 5 tonnes bull Transformerpower inverter 1 tonne bull Housing 19 tonnes
Key components of the tower section will include bull Ladders bull Lift bull Power inverter bull Power cable bull Control equipment bull Bolts bull Tower sections
Of these components the tower sections themselves will make up the bulk of the 250 tonne complete weight
Figure 14 Tower Section
A Decommissioning Proposal
It is intended that all the above components are fully removed from site before being disassembled onshore This reduces offshore risk for example in relation to spillage and facilitates safe deconstruction onshore
In terms of the key criteria this approach has been assessed as follows
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
Page 48 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
OFFSHORE WIND TURBINES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained inside the nacelle and removed in single lift All dismantling takes place onshore therefore minimizing the risk of spillage
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle
Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Knowntried procedures reduced risk due to minimal offshore works
422 Turbine Foundations amp Transition Pieces
A Component Description
A monopile solution has been selected for the turbine foundations for the Greater Gabbard offshore wind farm project This solution comprises driving a hollow steel pile into the seabed sub-strata relying on the frictional properties of the seabed sediments for support These structures will extend up to 65m in length 65m in diameter and 700 tonnes in weight
Foundations will require ancillary equipment including
bull Cable entry and protection features The cables are to be installed in a ldquoJ-tuberdquo arrangement a steel tube of approximately 250mm diameter located internally within the monopile Each structure will have between two and five J-tubes At the end of each J-tube cable entry will be facilitated by a bell-mouth shaped opening
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bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
Page 38 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
Page 41 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
Page 42 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Corrosion protection a combination of a protective paint coating and installation of sacrificial anodes on the subsea structure The anodes are standard products for offshore structures and are welded onto the steel structures The anodes typically consist of zinc and aluminium and are connected to the structure via doubler plates to ensure the integrity of the primary structure is maintained in the unlikely failure of an anode connection Cadmium will not be used The number and size of anodes will be confirmed during detailed design
bull Transition pieces making the connection between the foundation and the tower will weigh up to 300 tonnes and will include the following components
bull Boat fenders
bull Access ladders
bull Transformer (oil filled)
bull Switchgear (gas filled breakers)
bull Control equipment
bull Cables
bull Access deck
bull Handrail sections
bull Grating
bull Marine access door
An access platform comprising two access ladders (with integral personnel safety protection) will enable access to the wind turbine at any state of the tide The access ladders and platform will be constructed from steel The structures will have provisions for personnel safety eg life-rings The total weight of these arrangements is typically 10 tonnes per installation therefore 1400 tonnes of steel will be required for the 140 wind turbines
Figure 15 Monopile and Transition Piece at Arklow Bank (courtesy of GE Wind)
Page 36 of 58
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
Page 37 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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B Decommissioning Proposal
Design considerations have been made to ensure that the installations are affordable to remove However design codes and standards limit the ability to reduce steel thicknesses and to lighten the structures to ease future removal The result is that the monopiles are of a size that means they will not be able to be removed from the seabed once piled to the design penetration depth of approximately 35m below seabed Consequently it is proposed that the foundations are cut at or below seabed In the first instance a general target of cutting one metre below seabed is proposed though it may be necessary to vary the target depth for individual turbines subject to site specific factors such as the specific ground conditions at each turbine location It is noted that in order to overcome vast frictional forces considerable excavation will be needed In order to be able to undertake the cutting procedure the diameter of the excavation hole will increase by at least two metres for every additional metre in depth below seabed As such it may be considered too intrusive and damaging to consider cutting below one metre depth
It is proposed that following the cutting operation the foundations and transition pieces be removed as a single structure The total lift weight of this structure will be in the order of 660 tonnes
The following table compares and contrasts the options of complete removal of foundations with the alternative of cutting below seabed as described above The same considerations apply to the foundations used for transformer platforms and met masts
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
Safety for all at all times
High risk to personnel associated with lifting extreme weights Risk compounded by significant length of time
Fewer activities to be undertaken over a shorter time period offshore minimising risk to personnel
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
needed to undertake works Post decommissioning site monitoring offshore Diver operations will identify any unlikely exposure would be required with the result that safety risk is
insignificant
Consideration of the rights and needs legitimate users of the sea
Disadvantages to other users of the marine environment include disruption over a longer time period whilst the works are undertaken and remaining scour holes associated with excavation
No risk presented providing cutting is to sufficient depth site is monitored post decommissioning any unlikely exposure identified
Minimise environmental impact
Excavation pits over a wide area causing significant impact to marine environment Associated dumping of excessive volume of waste material also required Disturbance would take place over long time period Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Considerably reduced works footprint relative to complete removal Works would take place over reduced time period and involve less equipment Seabed recovery time shorter than complete removal scenario Some artificial reef habitat may be lost but long term risk of decay and pollution will be eliminated
Promote sustainable development
In the long term complete removal affords maximum flexibility over use of seabed though considerable destruction over the whole site in short-medium term
Some activities may be limited at turbine locations eg extraction (given incidence of london clay on site demand for extraction unlikely) Providing remaining structures do not become exposed most future activities will not be affected Seabed recovery is highly likely
Adhere to the Polluter Pays Principle
Consistent in principle assuming a suitable disposal solution can be found for the excavated waste material and that the seabed can be restored
Consistent as far as is reasonably practicable ndash all remains to be suitably buried
Maximise the reuse of materials
Maximum material potentially available for reuse
Less material available for reuse relative to complete removal
Commercial Viability
Not commercially viable ndash excavation and extreme lifting
Less expensive alternative to complete removal involving minimal
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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FOUNDATIONS Criterion Complete Removal Cutting Below Seabed
involves major equipment requirements over longer periods of time
excavation
Practical Integrity
Not a practical solution Extreme risk associated with heavy lift considerable excavation needed with associated storage or disposal of large volume of waste
Standard procedures and equipment
This analysis shows that cutting below seabed is preferable to complete removal on the grounds of safety practical integrity and commercial viability
GGOWL consider that there to be consistency between this proposal and the relevant circumstances set out in DTI guidance
bull entire removal would involve extreme cost
bull entire removal would involve an unacceptable risk to personnel
It is also noted that this approach is standard practice within the oil and gas industry for similar structures
Although GGOWL is committed to cutting foundations below seabed contingency plans will be put in place to ensure appropriate actions are carried out in the unlikely event that remaining structure(s) become exposed Please see Section 12 for details
423 Transformer Platforms
A Component Description
The purpose of an offshore sub-station platform is to transform the voltage of the electricity generated at the wind turbine to a higher voltage suitable for transmission of power to shore
Up to four offshore sub-stations will be required and located at strategic points within the turbine array The substations will have typical dimensions of 20m length x 20m width x 15m height The total height of the sub-station including the foundation will be up to 40m above LAT
The components within the sub-station offshore platforms will include
bull Medium to high voltage transformers
bull High voltage GIS (gas insulated switchgear)
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bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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bull Back-up diesel generator and tank
bull Accommodation facilities
bull J-tubes
bull Medium and high voltage cables
The foundations supporting transformer platforms include a four legged jacket and pin piles
The jacket structure will weigh approximately 450 tonnes with the piles each weighing approximately 200 tonnes and the topsides weighing 500 tonnes Figure 16 gives an indicative representation of an offshore transformer support structure
Figure 16 Indicative Transformer Support Structure
B Decommissioning Proposal
It is proposed that all topside structures and ancillary equipment be removed In particular as the transformers may be oil or resin filled they will be taken to shore complete reducing the potential for offshore spillage risk and facilitating safe deconstruction The complete lift weight will be in the region of 500 tonnes The justification for complete removal of the topsides is outlined below
PLATFORM TOPSIDES
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
Page 48 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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PLATFORM TOPSIDES
Criterion Complete Removal
of the sea
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
It is proposed that the four legged jacket including leg piles are cut to 1m below seabed This will involve a total lift of approximately 850 tonnes The justification for cutting foundations below seabed provided in section 422B above also applies to this proposal
424 Anemometry Masts
A Component Description
Permanent anemometry masts will be required for the operations phase Such masts will be the same height as the wind turbine hub ie up to 105m above mean sea level and will feature a foundation installed in a similar manner to the foundations for the wind turbines described above The anemometry masts will be connected to the wind turbine array using buried subsea cables
A anemometry mast consists of the following parts
bull Monopile foundation
bull Platform including boat landing
bull Met mast including instrumentation (above and possibly below water)
bull Control cabinet solar panels and batteries
bull Aerial and marine navigational lights and markings
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
Page 48 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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The foundations for the anemometry masts will consist of a steel monopile with a diameter of approximately 25m and a length of approximately 70m of which up to 30m will be driven into the seabed The monopile will be made of approximately 400 tonnes of steel Scour protection is not envisaged to be necessary
Figure 17 Existing Anemometry Mast at the Greater Gabbard Offshore Wind Farm Site
B Decommissioning Proposal
It is proposed that all anemometry equipment and supporting towers are completely removed and deconstructed onshore
The monopile foundation will be removed in accordance with the provisions made in Section 422 B It is estimated that approximately 29m would remain below the seabed The total lift weight of the removed section including the weight of the deck is approximately 200 tonnes
ANEMOMETRY MASTS
Criterion Complete Removal
Safety for all at all times Safest option involving standard procedures and minimal work offshore
Consideration of the rights and needs legitimate users of the sea
Complete removal of structure best long-term solution Appropriate notification and consultation would precede temporary worksdisturbance
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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ANEMOMETRY MASTS
Criterion Complete Removal
Minimise environmental impact
Risk of spillage slight as all pollutants are fully contained and removed in single lift All dismantling takes place onshore
Promote sustainable development
Materials completely removed from site ensures future generations do not suffer from a diminished environment or from a compromised ability to make use of marine resources
Adhere to the Polluter Pays Principle Entirely consistent owner pays full cost of removal and disposal
Maximise the reuse of materials
All deconstruction to take place onshore maximum potential for reuse of materials
Commercial Viability Most commercially viable solution minimal works offshore maximum re-salereuse value from materials minimum residual risk
Practical Integrity Main risk is heavy lift and this can be mitigated by use of correct procedures and capable vessels and equipment Most practical method
425 Cabling
A Component Description
Export Cables Subsea power cables are required to connect the wind farm to the electricity transmission system These cables will also comprise internal fibre optics for wind farm control purposes The 3-core cables will consist of copper conductors with integral insulation core screening and steel armour (for stiffness and impact resistance)
The export cables will be buried to a depth ranging between at least 10m and 15m below seabed It is considered that the proposed burial depths for export cables are sufficient to ensure that the cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely At the beach end of the cable route the export cables will be uncovered for a length below LAT
Inter-Array Cables The inter-array cables will be relatively short in length (typically 650 to 1200m) and will interconnect the wind turbines within the arrays to each other and to the offshore sub-station platforms The cables are expected to be standard 3-core copper conductor XLPE (or equivalent) insulated and armoured submarine cable rated at 33kV The cables have an external diameter of approximately 150mm
All cables are to be buried in the seabed to a nominal depth of 1ndash15m Where the inter array cables cross sandbanks burial shall be at 15m depth It is proposed that cables will be set into the London clay underlying the sand waves to ensure that they stay buried throughout the lifetime of the project and beyond
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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It is proposed that turbine interconnecting cables adjacent to the substructures are cut at a point below the surface of the seabed to allow the cable to remain buried The cut sections would be removed with minimal disruption of the seabed For any inter array cable crossing sand banks it would be proposed to leave in situ as the disruption caused by jetting and or excavating the sand bank to remove the cable is regarded as being detrimental to the seabed It is considered that these proposed burial depths are sufficient to ensure that the inter-array cables do not become exposed by the removal of overburden material Burial within clay as opposed to within mobile sediment ensures that cables remain buried indefinitely
The estimated total cable length for both export and inter-array cables is approximately 320 km Note that cables are not oilfluid filled
Figure 18 Typical cross section of 3 core copper XLPE armoured 33kv subsea cable representative of inter-array cables (courtesy Nexans)
Figure 19 Typical cross section of 13 core copper XLPE armoured 132kV subsea cable representative of export cables (courtesy Nexans)
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
Page 54 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
Page 55 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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B Decommissioning Proposal
At the time of writing GGOWL intends to follow the current industry standard by leaving both inter-array and export cables in-situ As such life-cycle costs and environmental impact will be considered in the design of the inter-array and export cables
Whilst it is considered that cables are buried at a safe depth contingency plans will be put in place to ensure appropriate actions are carried out if the cables do become exposed Please see Section 12 for details
An exception is made for the inter-tidal zone where GGOWL consider that the BEPO would be to cut and pull through the cables to the onshore jointing pit This operation would not impact the seabed
CABLES
Criterion Complete Removal Leaving in situ Safety for all at all times
Risk to personnel not excessive Burial within stable clay seabed does not pose safety risks to marine users
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
No risk presented from leaving buried cables in situ Potential for extraction activities limited (though unlikely in London Clay)
Minimise environmental impact
Given the considerable length of cable and the need for jetting techniques removal would cause considerable damage and disruption to the seabed and established communities These impacts could be considered large relative to the environmental gains from
Benign - no environmental impact associated with long term disintegration of buried cables
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
Page 50 of 58
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
Page 54 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
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CABLES
Criterion Complete Removal Leaving in situ removal
Promote sustainable development
Though considerable lsquotroughsrsquo would remain on the seabed in the short-medium term complete removal affords maximum flexibility over use of seabed in the long term
Some future activities may be limited eg extraction (unlikely on London clay)
Adhere to the Polluter Pays Principle
Consistent assuming suitable disposal option is found for surplus cable components
Benign no pollution risk
Maximise the reuse of materials
Maximum material eg copper potentially available for reuse No reuse possible if left in situ
Commercial Viability
Expensive operation offset to an extent by copper re-sale value
Limited cost involved with reshyburial of cable lsquoendsrsquo
Practical Integrity Possible to undertake Likely to cause damage to marine environment
NA
426 Scour Protection
A Component Description
Scour is the term used for the localised removal of sediment from the area around the base of support structures located in moving water When a structure is placed in a current the flow is accelerated around the structure If the bed is erodable (and the shear stresses are of sufficient magnitude) a scour hole forms around the structure This phenomenon is known as local or structure-induced sediment scour
Scour is not anticipated to be of concern at the Greater Gabbard offshore wind farm site given the underlying London Clay formation either exposed or with veneers of sand and gravel on top As such there is little perceived need for scour protection materials Nonetheless for the purposes of the EIA and this decommissioning programme it has been assumed that some scouring of the upper softer clay andor sand and gravel material may occur and as such scour protection measures around the structures such as rock dumping or fronded mattresses may be needed
For monopile foundations the procedure involves establishment of a thin rock layer installed prior to pile driving with a mean rock size (D50) of 100-300 mm This layer will typically be 24 m in diameter with a height of 05 m (ie a total volume of 226 m) After driving of the pile cover stones with D50 of between 400-750 mm are placed around the foundation The total diameter of the scour protection is assumed to be a maximum of 5 times the pile
Page 46 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
Page 50 of 58
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
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GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
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bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
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bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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diameter (D) ie the total volume of cover stones will be 1432 msup3 per foundation and up to 200480 m3 for 140 foundations
It is possible that cable protection measures will be required at the sandbank margins At the time of writing GGOWL do not have details of these measures but will revert to JNCC MFA and DBERR about all scour protection requirements once this information is available
B Decommissioning Proposal
In the unlikely event that scour material is required it is proposed that this is left in situ following decommissioning
Scour Material
Criterion Complete Removal Other
Safety for all at all times
Removal is a labour intensive activity involving divers and posing an unacceptable risk to personnel
Reduced risk for contractors Marginal increase in risk to marine users some additional rock over small areas at specific locations
Consideration of the rights and needs legitimate users of the sea
Removal affords maximum flexibility over use of seabed
May limit uses of seabed May generate positive habitat benefits
Minimise Removal will cause considerable damage Habitat for established environmental and disruption to the seabed and communities retained no short or impact established communities Associated
equipment and vessels will generate disturbance and additional noise over wide area These impacts could be considered large relative to the environmental gains from removal Materials gathered would need to be dumped elsewhere
long term detrimental effects on marine environment anticipated
Promote sustainable development
Consistent in principle assuming suitable disposal solution found
Prevents some future activities on the seabed Total area of sterilisation is small
Adhere to the Polluter Pays Principle
Consistent in principle Inferior option to complete removal in this regard
Maximise the reuse of materials
Opportunities for reuse of materials gathered are limited Materials would need to be disposed of elsewhere
NA
Commercial Expensive labour intensive high volume Costs limited to ongoing
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Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
Page 48 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
Page 50 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
Page 51 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
Page 52 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
Page 54 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
Scour Material
Criterion Complete Removal Other
Viability operation monitoring
Practical Integrity High reliance on manual work labour intensive Possible but not practical
NA
In relation to the circumstances set out in the DTI guidance where non-removal may be considered acceptable it is considered that in this instance ldquothe installation or structure will serve a new use hellip through the enhancement of a living resourcerdquo It is also considered that entire removal would involve an unacceptable risk to personnel
50 DESCRIPTION OF PROPOSED DECOMMISSIONING MEASURES
The methods of decommissioning will be affected by site specific factors by final design choices (for example in relation to foundation type) and by the equipment and vessels available at the time The measures described in this section are based on current technology and information but it should be recognised that the methods may evolve over time
Periodic review of the Decommissioning Programme and the measures proposed within it will take place throughout the lifetime of the wind farm to accommodate new information For example new offshore technologies are continually being evaluated tested and developed GGOWL expects considerable advances over the lifetime of the project with new techniques evolving as experience and knowledge in the sector grows In particular it is acknowledged that lessons may be learned through the construction and operation of the project and through industry experience in decommissioning renewable energy and other offshore installations Sufficient time must be given to researching the different available technologies for each phase of the decommissioning operation
It may also be necessary to amend these measures in order to comply with revised best practice guidelines and future legislation
Section 9 sets out a formal timetable for reviewing the decommissioning provisions for the Greater Gabbard offshore wind farm project in order to ensure that the best technology is selected and efficient and safe procedures are followed
51 Wind TurbinesGenerating Equipment
The decommissioning of the superstructure (ie removal of turbine components including blades nacelle and tower) is likely to be a reversal of the installation process
Opportunities to re-use the generating equipment will be maximised Health and Safety will be of paramount importance during decommissioning All work will follow the
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
Page 50 of 58
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In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
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60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
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bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
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bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
Page 54 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
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Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
recommendations and requirements of the CDM regulations (or applicable codes and standards at the time the work starts)
The general methodology for carrying this out is as follows
bull De-energize and isolate from Grid (may be undertaken in phases)
bull Mobilise suitable heavy lift vessel(s) to the wind farm location
bull Remove rotor component parts
bull Cut turbine interconnecting cables adjacent to the substructures
bull Remove nacelle including gearbox and generator
bull Remove turbine tower
bull Transport all components to an onshore site at which they will be processed for reuse recycling or disposal
Once onshore the structures and substructures will be reduced to sizes suitable for disposal as follows
bull Removal of all hazardous substances and fluids from the turbines (such as oil reservoirs and any hazardous materials and components) All components to be disposed of in accordance with relevant regulations
bull All steel components sold for scrap to be recycled This forms the bulk of the structures and substructures
bull The turbine blades (fibreglass) will be disposed of in accordance with the relevant regulations in force at the time of decommissioning One potential disposal method identified is to break down the fibreglass into a pulp for use as cavity insulation in buildings
52 Foundations
On current knowledge abrasive diamond wire cutting is likely to be the preferred method for cutting all the foundation structures at or below seabed The final method chosen shall be the least damaging to the surrounding seabed and most environmentally acceptable means available
The use of divers for any of the removal works will be minimised and if possible removed completely
Page 49 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
Page 50 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
Page 51 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
Page 52 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
Page 53 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
Page 54 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
Page 55 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
The general methodology for decommissioning of the wind turbine monopiles is likely to be as follows
bull Operate cutting procedure at or below seabed
bull Remove transition piece and upper part of monopile as a single object using suitable lifting vessel
bull Transport to onshore location for offloadingdisposal
bull Remove internal equipment disassemble onshore
53 Transformer Platforms
The decommissioning of the transformer platforms will follow similar method as described for the turbines and turbine foundations The complete lsquotopsidersquo structure will be removed in a single lift taken by suitable vessel to an onshore facility where the equipment and structure will be dismantled and the constituent parts processed for reuse recycling and or disposal
54 Anemometry Masts
The Anemometry masts are envisaged to be decommissioned by reversal of the installation procedure with the mast being removed with a relatively small crane barge The monopile will be cut-off below sea-bed level using similar technology to the large foundation monopiles
55 Cables
In light of the proposal to leave cables buried under the seabed the cable will be cut at a suitable point as close to the foundation as possible with the ends buried to a proposed depth of 1 metre below seabed level This will minimise the further disruption to the seabed and any established marine life in the area
56 Scour Protection
If required it has been proposed that any scour protection will be left in situ
57 Waste Management
GGOWL is committed to maximising the reuse of waste materials and pays full regard to the lsquowaste hierarchyrsquo which suggests that reuse should be considered first followed by recycling incineration with energy recovery and lastly disposal In any event waste management will be carried out in accordance with all relevant legislation and it would be intended that any disposal took place on land
Page 50 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
Page 51 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
Page 52 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
Page 53 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
Page 54 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
Page 55 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
In following the waste hierarchy and subject to evolution of technology change in regulations and demand for materials over the lifetime of the project the waste management of the main project components might involve
Waste Type Pre-treatment Disposal Recycle Reuse
Wind turbine foundations Establish available design life at end of 25 years
Reuse by repowering with newsuperior wind turbines or other renewable generation technology
Steel from wind turbine foundations tower and nacelle removed to shore
Break down into transportable size Recycle
Copper from power cables and transformers
Strip cable from power cables and transformers Recycle
Glass-fibre Reinforced Epoxy (GRE) from the blades
Break down into transportable size Recycle
Used lubricants from wind turbine Filter Recycle
Non-recyclable materials and fluids Landfill
As a part of the review process all appropriate regulations and guidelines will be reviewed A waste management plan will be drawn up well in advance of the commencement of decommissioning to ensure that adequate time remains for the proper provisions to be made
58 Lighting and Marking
In accordance with Clauses 4f and 5a of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL is committed to exhibiting the appropriate marks and lights during the decommissioning of the wind farm In relation to aviation safety the shape colour and character of the lighting will be compliant with the Air Navigation Order 2005 (or as otherwise directed by the Civil Aviation Authority)
In relation to navigational safety lights and marks will be agreed with Trinity House in consultation with the Maritime and Coastguard Agency In particular Trinity House will be consulted prior to decommissioning to specify any obstruction marking that may be required during the removal operations In the event that any obstruction is left on site that may be considered to present a hazard to navigation GGOWL will provide the necessary marking specified
Page 51 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
Page 52 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
Page 53 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
Page 54 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
Page 55 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
60 RE-POWERING
Whilst the design life for the project is 25 years the lease term for is 50 years As such GGOWLrsquos expectation is that the project will be lsquore-poweredrsquo midway through the lease term In comparison to full decommissioning as described above this is only likely to involve removing and replacing the turbine topsides and possibly some additional equipment such as that on the transformer platforms Nonetheless GGOWL acknowledges the UKrsquos international obligations that require that installations are decommissioned as soon as is reasonably practicable As such adequate provisions must be in place to ensure that the project can be fully decommissioned at year 25 in order that Government is not exposed to unacceptable risk This programme therefore sets out the measures for decommissioning the project at year 25
At this point GGOWL will present the case that re-powering is appropriate and achievable and seek approval from the Secretary of State that the agreed decommissioning programme be deferred in accordance with the remaining lease term for the project
70 ENVIRONMENTAL IMPACT ASSESSMENT
GGOWL completed an Environmental Impact Assessment (EIA) for the Greater Gabbard project between 2004 and 2005 The resulting Environmental Statement was submitted as part of the projectrsquos successful application for consent in October 2005 A lifecycle approach was taken in considering and assessing the impacts of the project and in seeking to mitigate and minimise the effect of the works In all instances a lsquoworst casersquo approach was taken to the assessment As such the assessment of the impact of the project on receptors and stakeholders takes into account decommissioning provisions that are either consistent or more onerous than those presented in this document
Consistent with the commitment to undertake reviews of the decommissioning provisions contained within this document it is proposed that the existing EIA is reviewed throughout the lifetime of the project A final review will be undertaken towards the end of the life of the installation when the final details of the decommissioning measures are known in order to address the impact of these has been appropriately assessed At this point a decision will be made as to whether a more detailed assessment is required Key criteria that will inform this decision include
bull Identification and assessment of potential impacts on the environment including exposure of biota to contaminants associated with the installation other biological impacts arising from physical effects conflicts with the conservation of species with the protection of their habitats or with mariculture have been identified
Surveys in and around the wind farm that could inform this process could include bull Benthic side scan sonar imaging bull Ornithological a single year programme to identify key species and assess
whether there are particularly sensitive times of year
Page 52 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
Page 53 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
Page 54 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
Page 55 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Marine Mammals should decommissioning activity give rise to high noise levels it may be appropriate to survey marine mammal activity
bull Review of Nature Designations
bull Identification and assessment of potential impacts relating to interference with other legitimate uses of the sea It is possible that the nature andor intensity of human activities taking place onaround the Greater Gabbard site such as commercial fishing may have changed over the lifetime of the project A review will be undertaken to identify those activities with potential to be affected by decommissioning
bull Identification and assessment of potential impacts on amenities the activities of communities and on future uses of the environment
bull Identification and assessment of potential impacts on historic environment interests
If required the final EIA will fill any lsquogapsrsquo in relation to the above It will also describe the measures envisaged to avoid reduce and if possible remedy any significant adverse effects indicated
The use of explosives is not proposed however should explosives be necessary during the course of decommissioning the potential impact of these on marine life particularly marine mammals will be assessed The use of explosives will be fully justified and a mitigation strategy proposed All appropriate guidelines and regulations such as those currently available from JNCC will be followed
80 CONSULTATIONS WITH INTERESTED PARTIES
GGOWL regard effective and open communication and consultation as essential elements to the successful development of the Greater Gabbard offshore wind farm project These principles were adopted during the development of the project and will be applied during the life of the offshore wind farm including the decommissioning phase of the project
GGOWL proposes to seek the advice and opinions of the following parties in drafting and reviewing the decommissioning programme for the project
bull Centre for Environment Fisheries and Aquaculture Science
bull Joint Nature Conservation Committee
bull Natural England
bull The Environment Agency
bull English Heritage
Page 53 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
Page 54 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
Page 55 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull The Maritime and Coastguard Agency
bull Trinity House Lighthouse Service
bull National Federation of Fishermenrsquos Organisations
bull Kent and Essex Sea Fisheries Committee
bull Chamber of Shipping
bull Royal Yachting Association
bull Harwich Haven Harbour Authority
bull British Marine Aggregate Producers Association
In order that the impact on legitimate marine users and stakeholders is minimised early and comprehensive consultation prior to decommissioning is required This strategy will be finalised and undertaken as part of the final review process undertaken prior to decommissioning
At the time of decommissioning and in accordance with Clauses 5c and 5d of the Greater Gabbard consent under Section 36 of the Electricity Act 1989 GGOWL will issue timely and efficient Notices to Mariners and other navigational warnings of the position and nature of the decommissioning activities that will be taking place Efforts will be made to ensure that this information reaches mariners in the shipping and fishing industry as well as recreational mariners The UK Hydrographic Office will be notified as appropriate on the progress and completion of the works
90 SCHEDULE AND THE REVIEW PROCESS
It is proposed that decommissioning commences at year 25 coinciding with the end of the design life of the turbines and the mid-life of the Crown Estate lease for the project
It is proposed that full decommissioning in accordance with the provisions described above will take 260 days to undertake bull Project management planning and procurement ndash 90 days bull Offshore decommissioning ndash 140 days bull Onshore works (including dismantling and disposal) ndash 170 days
Note that offshore decommissioning and onshore works will run in parallel A detailed programme of the works will be provided towards the end of the life of the project
GGOWL acknowledges that the most important steps in the decommissioning process are the planning ahead and the selection of the best decommissioning options As has been indicated throughout this document it is intended that the current decommissioning provisions are rigorously reviewed and assessed over the lifetime of the project
Page 54 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
Page 55 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
GGOWL intends to undertake internal reviews of the decommissioning programme throughout the life of the project and proposes that a formal review exercise is undertaken with DTI at the following times
bull 2 years following commencement of generation bull 10 years following commencement of generation (2 years prior to provision of
financial security) bull 18 years following commencement of generation (mid way through the period during
which financial security is provided)
It is proposed that a final review is undertaken in year 23 This will be the opportunity to finalise the detail of the decommissioning provisions schedule and costs As indicated in Section 7 this is also the opportunity to ensure that the impact of the works has been appropriately assessed and to determine in consultation with DTI and key stakeholders whether a revised EIA or Appropriate Assessment is necessary This will also be the final opportunity to consult with the stakeholders identified in Section 8 above about the details of the decommissioning provisions and the schedule of works
100 SEA-BED CLEARANCE
In accordance with the Polluter Pays Principle GGOWL proposes to clear the seabed in accordance with the provisions made in this decommissioning programme and to collect and provide evidence to reflect this
Following decommissioning surveys will be carried out to show that the site has been cleared These surveys will enable identification and subsequent recovery of any debris located on the sea-bed which may have arisen from activities related to the Greater Gabbard offshore wind farm and which may pose a risk to navigation other users of the sea or the marine environment It is currently intended that side scan sonar will be used to identify debris with an ROV deployed to investigate and recover any potential hazards identified
The area to be covered will be determined prior to decommissioning but GGOWL is aware of the guidance for oil and gas installations which specifies a 500m radius around any installation
Reference will also be made to the ldquoArchaeological No Build Areasrdquo in order that these are not inadvertently cleared in the process of removing any debris Analysis of the survey data will also ensure that items for removal and disposal relate only to the wind farm The appropriate competent authority will be approached regarding the identification of other anomalies that may be of archaeological interest
It is important that this process of collecting and presenting evidence that the site is cleared is independent GGOWL propose that an independent survey company complete the surveys and that they report in parallel to both GGOWL and DTI
Page 55 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
110 RESTORATION OF THE SITE
GGOWL is committed to restoring the Greater Gabbard offshore wind farm project site as far as is reasonably practicable to the condition that it was in prior to construction Consistent with the decommissioning provisions detailed above the key restoration work will relate to
bull Ensuring that foundations cut below seabed (turbines met mast platforms) are made safe and adequately covered
bull Ensuring that cable ends are adequately buried
Active restoration relying on intervention with equipment is not proposed as it is considered that such works present unnecessary and unacceptable risk to personnel Rather it is considered that allowing the seabed to lsquoself-settlersquo is sufficient and in proportion to the limited environmental impact of the proposed decommissioning
120 POST-DECOMMISSIONING MONITORING MAINTENANCE AND MANAGEMENT OF THE SITE
Given that GGOWL is not proposing to fully remove all installations some post decommissioning activities are proposed in order to identify and mitigate any unexpected risks to navigation or other users of the sea which may be posed by the remaining materials (for example where cables or foundations may have become exposed due to natural sediment dynamics)
The proposed post decommissioning activities are appropriate to
bull the scale and nature of the remaining infrastructure bull the degree of risk that any remains become exposed bull the degree of risk to marine users
Whilst the Greater Gabbard offshore wind farm project area is relatively large it is considered that the risk of exposure is extremely low primarily due to the depth at which foundations will be cut and cables buried and the relative stability of the seabed in the area In comparison to the oil and gas industry where the likelihood of debris falling overboard over the life of the installation is relatively high such risks are low for the Greater Gabbard project where offshore work associated with operations and maintenance is low and contained within the turbine structure
Given that the site is not heavily fished and that the distance offshore deters recreational users from the site it is also considered that the degree of risk to legitimate marine users is low
On the basis of this low degree of risk it is proposed that the following monitoring surveys are undertaken for elements left in situ beneath the sea-bed
Page 56 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Once at the time of completion of decommissioning
bull Annually for the following two years
bull Once after 5 years
bull Once after 10 years
At each proposed time GGOWL will perform a geophysical survey including a magnetometer survey on the site As indicated in section 10 above GGOWL propose to use an independent survey company to complete the surveys The company will be requested to report in parallel to both GGOWL and Government
In the event of protrusion or in the event that scour protection materials are left on site following decommissioning (see section 426) GGOWL will ensure that notification is given to the Hydrographic Office so that suitable notation of a potential anchoring hazard can be marked on relevant charts and mariners informed accordingly
It is noted that at the time of writing a solution for addressing residual liability has not been finalised Until a solution has been agreed GGOWL do not consider it appropriate to detail any specific management or maintenance procedures within this document
130 SUPPORTING STUDIES
The following documents inform and support the decommissioning provisions contained in the document
bull Greater Gabbard Environmental Statement October 2005
bull Appropriate Assessment with regard to the Greater Gabbard Offshore Wind Farm December 2006
bull Decommissioning of Offshore Renewable Energy Installations under the Energy Act 2004 Guidance notes for Industry DTI December 2006
bull Guidelines and Standards for the Removal of Offshore Installations and Structures on the Continental Shelf and in the Exclusive Economic Zone International Maritime Organisation (IMO) 19th October 1989
bull Guidance Notes for Industry Decommissioning of Offshore Installations and Pipelines under the Petroleum Act 1998 DTI httpwwwogdtigovukregulationguidancedecommissionhtm
bull Review of the Current State of Knowledge on the Environmental Impacts of the Location Operation and RemovalDisposal of Offshore Wind-Farms OSPAR 2006 ISBN 978-1-905859-15-3 wwwosparorg
Page 57 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58
Greater Gabbard Offshore Winds Limited Decommissioning Programme Greater Gabbard Offshore Wind Farm Project Fluor Project No 66577000 Airtricity Project No 403
bull Guidelines for Environmental Risk Assessment and Management Defra September 2002 httpwwwdefragovukenvironmentriskeramguide08htm
bull Guideline on Decommissioning Cost Estimation Turner amp Townsend Energy for UKOOA December 2006 wwwoilandgasorgukukooa
140 ANNEX A GREATER GABBARD ENVIRONMENTAL STATEMENT
Provided as a CD
150 ANNEX B GREATER GABBARD APPROPRIATE ASSESSMENT
160 ANNEX C GREATER GABBARD DECOMMISSIONING PROGRAMME FINANCIAL SECURITY ARRANGEMENT
Page 58 of 58