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Stamford Decommissioning Environmental Impact Assessment Page 3

TABLE OF CONTENTS

NON-TECHNICAL SUMMARY ....................................................................................................... 8

1. INTRODUCTION ............................................................................................................... 14

1.1 Location of the Stamford facilities ..................................................................................... 14

1.2 Project background and purpose ...................................................................................... 15

1.3 Regulatory context ............................................................................................................ 16

1.4 Purpose of the Environmental Impact Assessment .......................................................... 17

1.5 Stakeholder consultation ................................................................................................... 17

1.6 Business Management System including environmental management ........................... 18

2. PROJECT DESCRIPTION ............................................................................................... 20

2.1 Background information .................................................................................................... 20

2.2 Comparative Assessment ................................................................................................. 23

2.3 Decommissioning equipment and methods ...................................................................... 27

2.4 Summary ........................................................................................................................... 28

3. ENVIRONMENTAL BASELINE ....................................................................................... 31

3.1 Physical and chemical environment .................................................................................. 31

3.2 Biological environment ...................................................................................................... 40

3.3 Socioeconomic environment ............................................................................................. 48

4. EIA METHODOLOGY ....................................................................................................... 54

4.1 Overview ........................................................................................................................... 54

4.2 Impacts from planned activities ......................................................................................... 54

4.3 Impacts from unplanned events ........................................................................................ 58

4.4 Assessment of Impacts, Risks and Control Measures ..................................................... 59

5. ENVIRONMENTAL IMPACT ASSESSMENT .................................................................. 60

5.1 Energy use and atmospheric emissions ........................................................................... 60

5.2 Underwater noise .............................................................................................................. 66

5.3 Seabed disturbance .......................................................................................................... 68

5.4 Discharges and releases to sea ........................................................................................ 72

5.5 Large hydrocarbon releases and oil spill response .......................................................... 76

5.6 Waste ................................................................................................................................ 80

5.7 Socioeconomic impacts .................................................................................................... 83

6. CONCLUSIONS ................................................................................................................ 87

7. REFERENCES .................................................................................................................. 90

APPENDIX A – ENVIRONMENTAL WORKSHOP OUTPUT ....................................................... 97

APPENDIX C – OPEP MODELLING .......................................................................................... 109


FIGURES AND TABLES

Table: 0-1: Summary of Stamford subsea facilities decommissioning ........................................... 9 Table 1-1: Summary of stakeholder comments ............................................................................ 18 Table 2-1: Content of umbilical cores ........................................................................................... 22 Table 2-2: Comparative Assessment options for the pipeline and umbilical ................................ 24 Table 2-3: Summary of decommissioning programmes ............................................................... 25 Table 2-4: Vessel requirements for pipeline decommissioning .................................................... 28 Table 2-5: Vessel requirements for umbilical decommissioning ................................................... 29 Table 3-1: Folk Classification for the sediments surveyed April 2014 [30] ................................... 36 Table 3-2: Summary of contaminant concentrations at well head (20 & 22) ................................ 38 Table 3-3: Summary of contaminant concentrations at Markham Platform and typically found in southern North Sea surface sediments [20] & [22] ....................................................................... 39 Table 3-4: Seabird vulnerability to oil pollution in the vicinity of the proposed development [39] . 43 Table 3-5: Annex I habitats considered for SAC selection in UK offshore waters [42] ................. 45 Table 3-6: Sightings of cetaceans in the area surrounding Stamford [28]. ................................... 47 Table 3-7: Fishing effort by UK fishing fleet in ICES rectangle 36F2 compared with UK total [32] ...................................................................................................................................................... 50 Table 3-8: Total landings by UK fishing fleet in ICES rectangle 36F2 compared with UK total [32] ...................................................................................................................................................... 51 Table 3-9: Key environmental sensitivities ................................................................................... 53 Table 4-1: Duration / frequency of an aspect ................................................................................ 54 Table 4-2: Consequence / severity of an environmental aspect ................................................... 55 Table 4-3: Significance of environmental impact .......................................................................... 57 Table 4-4: Environmental impact acceptance criteria ................................................................... 58 Table 4-5: Likelihood of an unplanned activity / event occurring .................................................. 58 Table 4-6: Centrica Energy Upstream HSE Risk Assessment Matrix .......................................... 59 Table 4-7: Risk acceptance criteria .............................................................................................. 59 Table 5-1: Energy use and atmospheric emissions associated with pipeline decommissioning including associated mattresses and grout bags [51] ................................................................... 62 Table 5-2: Energy use and atmospheric emissions from umbilical decommissioning including associated mattresses and grout bags [51] .................................................................................. 63 Table 5-3: Total Direct and Indirect energy use and atmospheric emissions. .............................. 63 Table 5-4: Estimate of seabed area impacted from decommissioning activities .......................... 70 Table 5-5: Inventory disposition .................................................................................................... 82 Table 5-6: Re-use, recycle & disposal aspirations for material recovered to shore ...................... 82 Table 5-7: Cumulative Legacy Seabed Take ................................................................................ 85 Figure 0-1: Stamford location map ................................................................................................. 8 Figure 1-1: Stamford location ....................................................................................................... 14 Figure 1-2: Stamford field layout ................................................................................................... 15 Figure 2-1: Stamford pipeline system battery limits ...................................................................... 20 Figure 2-2: Stamford wellhead protection structure and xmas tree .............................................. 21 Figure 2-3: Stamford umbilical cross section ................................................................................ 22 Figure 2-4: Sketch showing locations of rock dump and pipeline cut locations ............................ 23 Figure 2-5: Selected option – partial removal ............................................................................... 25 Figure 2-6: Gantt chart of project plan .......................................................................................... 27 Figure 3-1: Bathymetry survey results and sample locations [22] ................................................ 33 Figure 3-2: Current data [3] .......................................................................................................... 34 Figure 3-3: Mean wind direction for the Stamford area [3] ........................................................... 35 Figure 3-4: Seabed and grab photographs [21] ............................................................................ 37


Figure 3-5: Seabed photograph from station 01 [22] .................................................................... 41 Figure 3-6: Seabed photograph from station 14 [22] .................................................................... 42 Figure 3-7: The spawning and nursery grounds of some fish species surrounding Stamford [3] . 44 Figure 3-8: Sensitivities within the Stamford area ........................................................................ 46 Figure 3-9 Oil and gas infrastructure in the vicinity of Stamford ................................................... 48 Figure 3-10: Location of wind farm areas in relation to Stamford [3] ............................................ 49 Figure 3-11: Live catches within ICES rectangle 36F2 by species type [32]. ............................... 51 Figure 3-12: Fish catch by EU member state in ICES Divisions IVb and IVc in 2012 [32] ........... 52 Figure 3-13: Share of landings in the UK North Sea by EU member states in 2013 [32] ............. 52 Figure 5-1: Waste Hierarchy ......................................................................................................... 81 Figure 5-2: Estimated materials to shore: pipelines ...................................................................... 83


TERMS AND ABBREVIATIONS

ABBREV. DESCRIPTION ABBREV. DESCRIPTION

ALARP As low as is reasonably practicable MCAA Marine and Coastal Access Act

AoS Areas of Search MCZ Marine Conservation Zone

BEP Best Environmental Practice NFFO National Federation of Fishermen's Organisations

BODC British Oceanographic Data Centre MPA Marine Protected Area

CA Comparative Assessment MPZ Marine Protected Zone

Centrica Centrica Energy Exploration and Production (CE E&P) NORM

Naturally Occurring Radioactive Material

CEFAS Centre for Environment, Fisheries and Aquaculture Science NOX Nitrous Oxides

CO2 Carbon Dioxide OPEP Oil Pollution Emergency Plan

cSAC Candidate Special Area of Conservation OSPAR Oslo and Paris Convention

CT Compression Tower P&A Plugging and Abandonment

DECC EMT

Department of Energy and Climate Change Environmental Management Team PAH Polycyclic Aromatic Hydrocarbon

Direct / Indirect impacts or emissions

Impacts or emissions that are owned or controlled by Centrica / a consequence of the activities but are owned or controlled by an entity other than Centrica. PPE Personal Protection Equipment

DSV Diving Support Vessel QMS Quality Management System

EC European Commission QSE Quality, Safety and Environment

EEC European Economic Community ROVSV Remotely Operated Vehicle Support Vessel

EIA Environmental Impact Assessment SAC Special Area of Conservation

EMP Environmental Management Plan SCIs Sites of Community Importance

EMS Environmental Management System SO2 Sulphur Dioxide

ESDV Emergency Shutdown Valve SOPEP Shipboard Oil Pollution Emergency Plan

EU European Union SUTU Subsea Umbilical Termination Unit

EUNIS European Nature Information System THC Total Hydrocarbons

GJ Gigajoule TOC Total Organic Carbon


ABBREV. DESCRIPTION ABBREV. DESCRIPTION

HSE Health, Safety and Environment TOM Total Organic Matter

ICES International Council for the Exploration of the Sea TSS Traffic Separation Schemes

ISO International Organization for Standardization THC Total Hydrocarbons

JNCC Joint Nature Conservation Committee TUTU Topside Umbilical Termination Unit

Km Kilometre UKCS United Kingdom Continental Shelf

LAT Lowest Astronomical Tide VOCs Volatile Organic Compounds

MAFF Ministry of Agriculture, Fisheries and Food WFD Waste Framework Directive

Markham Platform

Markham Compression Tower and J6A Platform WHPS Wellhead Protection Structure

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the middle of 2012 due to aquifer encroachment. Gas was exported to Den Helder in the Netherlands, via the J6A Compression Tower (Markham Platform), the Wintershall operated K/13 platform and the Westgastransport pipeline.

The Cessation of Production (CoP) for the Stamford Field has been approved by DECC.

A summary of the Stamford facilities is provided in Table i.

Table: 0-1: Summary of Stamford subsea facilities decommissioning

Section of UKCS Southern

Distance from English Coast 140km

Water depth 34.7m

Distance of Stamford well from UK/Netherlands median line

5.1km

Latitude / Longitude 53º 48` 15.126”N and 02º 50` 13.368”E

License Block Block 49/10c

License number P1447

Owner:

Operator:

Centrica North Sea Gas Limited

Centrica Production Nederland B.V from 2009.

At the time of the original application for the Stamford development EIA in April 2008, ownership and operational control ultimately rested with Venture Production plc which was later acquired by Centrica plc in 2009.

Lifespan at development 3 years

Design life 5 years

Cessation of production approval date August 2014

Facilities subsea well

wellhead protection structure

gas pipeline (6” x 7.331 km) with 40m spool pieces at the well

flexible riser (0.2 km)

control umbilical (5” x 7.683 km, multi-core)1

concrete mattresses (64 in total)

grout bags (approximately 200 in total)

rock (approximately 5,536 tonnes in the UK and 3,847 tonnes in the Netherlands)

1The umbilical carries hydraulic fluid, corrosion inhibitor and methanol in addition to the power and signal required for the control and operation of the wellhead and pipeline.

Regulatory context

Decommissioning of offshore oil and gas facilities on the UK Continental Shelf (UKCS) is governed by a range of legislation and guidance but falls principally under the Petroleum Act 1998 (as amended by the Energy Act 2008) [1]. The Petroleum Act sets out the requirements for a formal Decommissioning Programme, which must be approved by the Department of Energy and Climate Change before decommissioning commences. The Department of Energy and Climate Change Guidance Notes [2] require that the Decommissioning Programme is supported


by an environmental impact assessment which considers the potential environmental impacts.

Decommissioning of offshore oil and gas facilities in the Dutch Continental Shelf is governed by the Mining Act, the Mining Decree and the Mining Regulation, under the authority and supervision of the Minister of Economic Affairs and the State Supervision of Mines.

Environmental management

Centrica operate an environmental management system which is certified to the requirements of the international environmental management systems standard BS EN ISO14001:2004.

Decommissioning summary

Prior to decommissioning of Stamford, a range of preparatory activities will be completed. These will include depressurising, pigging and flushing the gas pipeline and flushing of the umbilical cores. Both the pipeline and umbilical cores will be left flooded with treated water.

6” Pipeline

The gas pipeline will be decommissioned following a Partial removal approach, as it is sufficiently buried under the seabed and with rock cover with the exception of the pipeline ends and spool pieces which will be recovered.

Activities will include its disconnection from the wellhead and the flexible pipeline riser, which connects it to the Markham Platform. The flexible pipeline riser will remain flooded and in situ for potential re-use. The spool pieces will be removed. The pipeline ends will be cut back leaving no projection on the seabed. The rock cover will remain to continue to provide protection for the decommissioned pipeline.

5” Control Umbilical

The umbilical will be decommissioned following a Partial removal approach, as it is sufficiently buried under the seabed and with rock cover with the exception of the ends which will be recovered.

The umbilical will be disconnected from the wellhead and platform by cutting close to each end. The short lengths above the cut at the platform end and the well end will be recovered. The remainder of the umbilical will remain in the seabed or covered with rock.

Wellhead Protection Structure (WHPS)

The wellhead protection structure (WHPS) will be removed and returned to shore for reuse or recycling.

The WHPS will be recovered and if practicable reconditioned for reuse. The wellhead assembly itself will be recovered as part of the well plug and abandon activities.

Concrete mattresses and grout bags

Recovered from the wellhead end and left in place over the flexible pipeline in the 500m exclusion zone at the platform end for re-use and decommissioned with the Markham Platform.

The mattresses and grout bags will be removed from the well end of the lines prior to disconnection and dismantling activities. They will be lifted to a support vessel for onshore disposal. The mattresses and grout bags at the Markham Platform end of the lines will remain in place for reuse.

Following the completion of all activities, an over trawl sweep of the area will be conducted to ensure that there are no projections which might snag fishing trawls.

Environmental setting and sensitivities

Stamford is located at a water depth of approximately 34.7m, in an area that is typical of the offshore regions of the southern North Sea, where hydrographical, meteorological, geological and biological characteristics are relatively uniform over large areas. Commercial users of the area are mainly associated with oil and gas exploration and development, shipping and fishing.

The seabed sediment consists mainly of sand, gravel and muds and the area is mainly smooth, apart from a channel in the south west and a raised feature in the north east. The shallower sea depth allows hydrodynamic processes such as prevailing currents to cause changes over time to


sediment composition and distribution at the seabed.

The ecosystem comprises a wide range of fauna from planktonic species through to molluscs, crustaceans, various fish species and larger marine mammals such as harbour porpoise, minke whales and dolphins. The area is known to be a spawning ground for mackerel, herring and cod and offers low to moderate value as a commercial fishery.

A range of seabirds are commonly observed. Many of these species may be sensitive to disturbance but the decommissioning activities are relatively short term, therefore significant disturbance is unlikely.

Impacts

Energy use and emissions to air

The principal energy use and generation of emissions to air arise from fuel combustion for propulsion and power generation by the vessels required for the activities. These emissions will include components which have the potential to contribute to global warming, acid rainfall, dry deposition of particulate and photochemical pollution or cause impacts on local air quality. It is expected that impacts will be of low significance as they will be short term.

Emissions to air will be minimised by planning intended to minimise the duration of vessel use (optimising vessel schedules). All equipment will be maintained for efficient operation and fuel consumption will be continuously monitored.

Underwater noise

Underwater noise has the potential to impact on marine mammals and other species. The subsea noise levels generated by the vessels to be used in the decommissioning are unlikely to result in physiological damage. The duration of the impact will be short term and has been assessed as of low significance. Activities such as underwater cutting and the use of dynamic positioning systems on support vessels will be planned and closely controlled which will minimise noise emissions.

Seabed disturbance

Activities being undertaken at or near the seabed have the potential for localised seabed disturbance. The activity which will lead to greatest disturbance of the seabed is the lifting of sections of pipeline and umbilical for recovery onto a vessel. Once this activity is completed it is expected that the seabed and its associated ecosystem will rapidly recover. Significant impacts of seabed disturbance are not anticipated.

Discharges to sea

Planned discharges to sea include routine operational discharges from the vessels and releases of residual contamination from the pipeline and umbilical when containment is broken.

Routine discharges from support vessels are not expected to cause significant impacts since the prevailing hydrodynamic conditions will ensure rapid dispersion of the discharges will be short term. These discharges are within the normal scope of shipping activities.

Discharges during pipeline disconnection will consist of residual contamination as the pipeline and umbilical will have been cleaned and flooded with water prior to decommissioning, with the exception of the cores filled with relatively benign OCNS D category Aqua-Glycol 24F and AQUALINK 300F VER2 in the umbilical. The quantity of materials involved will be small and rapidly dispersed by hydrodynamic conditions at the seabed. Therefore, the significance of the


associated impact will be low.

Releases to sea

The potential for accidental events (releases to sea) involving the release of polluting materials such as hydrocarbons or chemicals is unlikely to occur from the Stamford facilities, owing to the stringent control measures and operational procedures which are in place.

There is the potential for release to sea of a significant quantity of diesel from the vessels. Although the likelihood of such an event is extremely low, the potential impact has been assessed. This was done by reviewing the existing modelling of the behaviour of a larger spillage in the Oil Spill Contingency Plan from the Markham Platform. This modelling is inherently conservative in relation to the likely worst case scenario for the Stamford decommissioning activities. Emergency response measures are in place which will mitigate the impact of any accidental diesel spillage. The modelling results demonstrate that impact from a release of diesel is likely to be short term and do not predict significant impacts.

Waste

The decommissioning of Stamford will generate both hazardous and non-hazardous waste materials. Wastes will be segregated according to characteristic and their disposal route will be determined according to the waste hierarchy, taking account of the potential for recycle or recovery for reuse. Landfill disposal of waste will be avoided if at all possible and will only be used as a last resort.

Wastes will include concrete (mattresses and grout bags) and scrap metal (primarily steel). It is not expected that there will be any naturally occurring radioactive material arising from the decommissioning of Stamford. However, if there is it will be handled appropriately.

Waste management activities will be conducted in full compliance with all relevant legislation and regulatory controls, including shore side regulations for those wastes transferred ashore for treatment or disposal.

Socio-economic impacts

Impacts on commercial activities, such as fisheries, oil and gas operations and shipping will be low.

Access to the area for fishing will be restricted whilst decommissioning is undertaken, although the majority of the activities will be undertaken within the existing 500m exclusion zones at the wellhead and at the Markham Platform. This will lead to a short term impacts on the fishing industry although the impact will be low owing to the short duration and relatively small area of the activities.

The most beneficial socio-economic impact will be the short-term continuation of jobs in onshore yards and on vessels. However, it is expected that the overall impact will be low since the local socio-economic system is already altered owing to the presence of the oil industry itself.

Stamford is located within an area licensed for wind farm development but it is unlikely that there will be any impact on such development. Post decommissioning, the presence of the buried pipeline and umbilical may present a small restriction to the locating of turbines, however the area is small when compared to the size of the area licenced for the windfarm. Therefore, overall the impact is expected to be low.

Although the pipeline and umbilical will be left in situ, a post decommissioning sweep will verify that no obstructions likely to snag fishing trawls remain. In the longer term, the decommissioning of Stamford may have a positive impact on the fishing industry as a result of improved access


due to the removal of the 500m exclusion zone around the wellhead.

Overall, significance of the socio-economic impacts as a result of the decommissioning is expected to be low, with the exception of the fishing sector, where there is potential for a small positive impact.

Conclusions

An environmental workshop was undertaken to identify all impacts and risks associated with the decommissioning activities. During the workshop it was identified that the impacts and risks are reduced to ALARP within process by the identification of appropriate control and mitigation measures.

Overall, the environmental impact assessment concludes that the potential for significant impacts as a consequence of decommissioning Stamford is low. Generally, the impacts identified were assessed as short term and localised with low potential for long term or wider field impacts.


1 INTRODUCTION

This Environmental Impact Assessment (EIA) report is a supporting document to the Decommissioning Programme required by the Department of Energy and Climate Change (DECC) for the decommissioning of offshore installations. This EIA presents the environmental impacts and findings of the process undertaken by Centrica relating to the decommissioning of Stamford. The Venture North Sea Gas Limited Environmental Statement: Stamford Development (3), which was approved for the installation of the facilities, was referred to for the EIA and this report.

1.1 Location of the Stamford facilities

Stamford is located within the southern North Sea in the United Kingdom Continental Shelf (UKCS) Block 49/10c (see Figure 1-1 for the site field plan) lying approximately 140km from the English Coast and 7km from the Markham Platform. The pipeline crosses the median line to the Markham Platform in the Netherlands Sector.

Figure 1-1: Stamford location

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1.3 Regulatory context

The relevant UK and International legislation is outlined below. A summary of the Netherlands approach to decommissioning is also provided.

The UK and NL international obligations on decommissioning are governed principally by the 1992 Convention for the Protection of the Marine Environment of the North East Atlantic (OSPAR Convention) [5]. The OSPAR Decision 98/3 [6] sets out the UK’s international obligations on the decommissioning of offshore installations. However, pipelines and umbilicals, such as PL2567 and PLU2568 at Stamford are not included within the decision.

The decommissioning of offshore oil and gas infrastructure (including pipelines) in the UKCS is principally governed by the Petroleum Act 1998 (as amended by the Energy Act 2008) [1]. The Petroleum Act sets out the requirements for a formal Decommissioning Programme, which must be approved by DECC before the owners of an offshore installation or pipeline may proceed with decommissioning.

DECC Guidance Notes, [2] on the Decommissioning of Offshore Oil and Gas Installations and Pipelines, advise that any Decommissioning Programme must be supported by an EIA. The EIA will also be used to support NL requirements.

The DECC Guidance states that the EIA should include an assessment of the following:

All potential impacts on the marine environment including exposure of biota to contaminants; other biological impacts arising from physical effects; conflicts with the conservation of species and their habitats.

All potential impacts on other environmental compartments, including emissions to the atmosphere, leaching to groundwater, discharges to surface fresh water and impacts the soil.

Consumption of natural resources and energy associated with reuse and recycling.

Interference with other legitimate uses of the sea and consequential impacts on the physical environment.

Potential impacts on amenities, the activities of communities and on future uses of the environment.

The Marine and Coastal Access Act 2009 (MCAA) [4] states that an EIA is required for all licence applications relating to decommissioning operations. The MCAA licence application will be made at the time of decommissioning.

Other relevant legislation includes:

The Offshore Petroleum Activities (Conservation of Habitats) Regulations 2001 [8];

The Offshore Chemical Regulations 2002 [9];

The Offshore Petroleum Activities (Oil Pollution Prevention and Control) Regulations 2005 [10];

The Merchant Shipping (Oil Pollution Preparedness, Response and Co-operation Convention) Regulations 1998 (requiring an OPEP) [11];

The Offshore Petroleum Production and Pipe-lines (Assessment of Environmental Effects) Regulations 1999 [12];

Environmental Protection Act 1990 [13];


Special Waste Regulations 1996 [14];

Hazardous Waste (England and Wales) Regulations 2005 [15];

Transfrontier Shipment of Waste Regulations 2007 [16];

Transfrontier Shipment of Radioactive Waste and Spent Fuel Regulations 2008 [17].

As part of the requirements of the ISO14001 certified EMS, Centrica has identified all applicable legal and other requirements associated with the decommissioning work.

1.3.1 Overview of Dutch requirements

The main relevant legislation in the Netherlands which concerns the decommissioning of offshore installations comprises of the Mining Act, the Mining Decree and the Mining Regulation. The Mining Act gives principal regulatory powers in upstream oil and gas, apart from environment and planning in general, to the Minister of Economic Affairs (MEA) and the State Supervision of Mines (SSM). The SSM fall under the competence of the MEA. The SSM have a mission to ensure that all mineral extraction is carried out in a responsible and socially acceptable manner and a vision which insures that: “As few accidents and incidents and as little environmental pollution and nuisance as possible; Optimum use of present infrastructure for exploiting minerals and geothermal energy; Full use of the possibilities available to store natural gas and carbon dioxide deep underground; and the commitment of companies responsible for putting the above into practice”. The Mining Act prescribes that installations that are no longer used must be removed, including scrap and other materials at or immediately near such installations. The MEA may limit the obligation to a certain depth, to be determined at its discretion, beneath the soil of the surface water and may set a time frame within which the obligation must have been fulfilled. The decommissioning regime with respect to cables and pipelines situated on the Dutch part of the continental shelf is slightly different in that the removal obligation does not exist by force of law, but applies if and to the extent that the MEA has ordered the removal.

1.4 Purpose of the Environmental Impact Assessment

As described in the DECC guidance [2], this EIA report has been produced following the EIA guidance for the Offshore Petroleum Production and Pipelines (Assessment of Environmental Effects) Regulations (1999, as amended [12]). This EIA report presents the findings of the process and has been prepared for submission as part of the planning and consents requirements. The purpose of the EIA is to understand and communicate the significant environmental impacts associated with the project and to identify the required control and mitigation measures.

The EIA and this report, assesses potential impacts in the UKCS and the NLCS to provide an overall assessment of the impact, and to support both the UK and NL legislative requirements.

1.5 Stakeholder consultation

Stakeholder consultation is an important and significant part of the decommissioning process. Responses from stakeholders that are relevant to the EIA are shown in Table 1-1 and will be addressed as the project progresses.


Table 1-1: Summary of stakeholder comments

Stakeholder Comment Response

STATUTORY CONSULTATIONS

NFFO Advice given was to start discussions around 1 year before decommissioning.

Discussed at regular meetings with no concerns raised to date.

Continue discussions

DECC The EIA report should cover the scope of the decommissioning programmes, not including well P and A.

Infrastructure located in the Netherlands should be assessed. All impacts should be discussed together in the report but parts in the Netherlands should be highlighted

Centrica to check Markham Agreement obligations with respect to the changes at the Markham Platform, in the Markham field.

Included in this report.

1.5.1 Future consultation

The formal consultation will begin with the submission of the consultation draft Decommissioning Programmes and the submission of this EIA report in support of the Decommissioning Programmes to DECC. The consultation process at this stage will include the use of the Centrica website to make these documents available as well as hard copies being available in the Centrica Aberdeen office for inspection by members of the public.

1.6 Business Management System including environmental management

The management of the decommissioning operations is addressed within the Centrica Environmental Management System (EMS) certified to the requirements of ISO14001:2014. The EMS includes the procedures for the environmental management in line with the Company’s HSE policies and the appropriate legislation.

1.6.1 Environmental management

Centrica has a commitment to health, safety and security these are outlined below:

The health, safety and security of our employees, customers and others who may be affected by our activities are a top priority. We believe that all work-related fatalities, injuries and illnesses can be prevented and we are committed to ensuring that all employees work in a safe and healthy way.

The company’s Business Management System (BMS), which describes those controls required to address QSE risks, is designed to meet business needs and to adopt a consistent approach to QSE management by satisfying the requirements of the recognised, applicable management systems standards, for environment, ISO 14001 Environmental management systems.

Centrica also has a commitment to the environment and details of this are outlined below:

We are committed to understanding, managing and reducing the environmental impact of our


activities. In particular we are committed to playing our part in the transition to low carbon energy, while ensuring the security of present and future energy supplies. We aim to achieve this by sourcing and producing energy from cleaner sources, reducing wasted energy and developing and deploying new technology.

We aim to reduce the carbon intensity of our power generation by developing renewable energy sources. We are also committed to leading the consumer market for low carbon energy products and services, helping customers to reduce their energy usage.

We recognise that our operations, together with the way we deliver products and services, can have a major impact on the environment. For example, in the way we produce and use energy, manage our local environment and its biodiversity, operate our fleet of vehicles and manage the waste we create. We will work with our employees and suppliers to reduce these impacts through innovation, technology and cultural change. In addition we will quantify, measure and communicate our environmental performance in a rigorous and clear manner.

1.6.2 Contractor management

Centrica will appoint a project management team to select and manage the operations of competent contractors for well abandonment, decommissioning, and removal scopes of work. The team will ensure the decommissioning is executed safely, in accordance with Centrica Health and Safety principles and safeguard the environment in line with the environmental policy. Any change to the proposed decommissioning activities will be discussed with DECC.


2 PROJECT DESCRIPTION

This section presents a description of the Stamford facilities to be decommissioned, the process followed to identify the recommended decommissioning approach and an outline of the methodology that will be utilised in the decommissioning work.

2.1 Background information

The Stamford Development comprises a single subsea well, tied back to the Markham Platform, connected via a 7.331km production pipeline and a control umbilical of 7.683km.

Figure 1-2 shows the field layout and Figure 2-1 shows the battery limits of the pipeline system. The platform is not part of the scope.

Figure 2-1: Stamford pipeline system battery limits

At the upstream end of the pipeline system is the Stamford well, with wellhead, xmas tree, Subsea Umbilical Termination Unit (SUTU) and Wellhead Protection Structure (WHPS) which sits over the top of the tree with a 500 metre exclusion zone. The WHPS and tree are shown in Figure 2-26” Gas Pipeline (PL2567)

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Page 21

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Each core has a total volume of approximately 2m3 with the exception of three of the hydraulic cores which are approximately 1m3. The content of the cores at the time of decommissioning is shown in Table 2-1.

Table 2-1: Content of umbilical cores

Core Approximate Volume Content at decommissioning

Methanol Cores (1x) 2m3 Water with methanol residues

Corrosion Inhibitor Cores (1x) 2m3 Water with corrosion inhibitor residues

Hydraulic Cores (6x) 10m3 AQUALINK 300F VER2

Spare with Aqua-Glycol 24F (2x) 4m3 Aqua-Glycol 24F

As with the pipeline, the control umbilical is in a separate trench and backfilled with seabed material of greater than 0.6m for the majority of the length.

2.1.3 Rock dump, mattresses and grout bags

As stated above, both the pipeline and the umbilical have areas of rock dump, nine locations with a total of 5,356 tonnes in the UK sector and two locations with 3,847 tonnes in the NL sector. The locations of the rock dump are shown in Figure 2-4.

The pipeline and umbilical are protected with concrete mattresses at both ends where they emerge from the trenches within the 500m safety zones. There are 32 mattresses at the well end in the UKCS and 32 at the Markham Platform in the NLCS.

Grout bags (25kg) have been used to fill voids, give protective cover and provide smooth transitions between the pipe and the seabed around the mattresses. There are approximately 100 grout bags at the well end in the UKCS and another 100 grout bags at the Markham Platform end in the NLCS.


Figure 2-4: Sketch showing locations of rock dump and pipeline cut locations

2.1.4 Summary of facilities to be decommissioned

The facilities and materials to be decommissioned are:

WHPS

Pipeline Spools

Pipeline and flexible riser

Umbilical and subsea umbilical termination unit (SUTU)

Concrete Mattresses

Grout Bags

The wellhead and tree are also to be removed, but are covered under the offshore installation and wells (Design and Construction etc.) Regulations 1996 [18] in accordance with the oil and gas UK guidelines for the suspension and abandonment of wells. These items of infrastructure will be under a separate decommissioning campaign undertaken from a Drilling Rig and hence not assessed in this document. They will be assessed in the relevant permits at the time. The rock will remain in situ and isn’t discussed further.

2.2 Comparative Assessment

The Comparative Assessment (CA) [19] of pipeline and umbilical decommissioning options is a key supporting document of the decommissioning programmes submitted to the DECC. Its purpose is to recommend a decommissioning approach by following a guided assessment process involving five specified DECC evaluation criteria; safety, environment, cost, technical and societal issues [2].

Centrica conducted a CA for the gas pipeline and umbilical following the DECC guidance and Centrica guidance. The CA considered the two most feasible decommissioning options for the pipeline and umbilical: ‘Complete removal’ of the pipeline, spool pieces, and ‘Partial removal’,


involving leaving the buried pipeline in place, removing the spool pieces and cutting back the short pipeline which are not buried to an acceptable depth or covered with rock. The umbilical was considered along similar lines, also with a ‘Complete removal’ and a ‘Partial removal’ option (where, like the pipeline, the majority remains in situ). Table 2-2 outlines the two options. For constancy, this is as stated in the comparative assessment.

Table 2-2: Comparative Assessment options for the pipeline and umbilical

Item Option 1

Complete Removal

Option 2

Partial Removal

Buried Pipeline (UK & NL) Remove Leave in place

Exposed pipeline ends in Stamford 500m exclusion zone (approx. 12 metres total UK & NL)

Remove Cut and remove

Exposed pipeline ends in the Markham 500m exclusion zone

Remove Cut and remove

Tie-In Spools @ Stamford (39.2m, UK)

Remove Remove

Flexible riser, 200m long in the Markham 500m exclusion zone

Leave in situ with the Markham Platform for possible reuse for decommissioning in future

Leave in situ with the Markham platform for possible reuse for decommissioning in future

Umbilical Remove protected length inside the Markham 500m exclusion zone to be decommissioned with the Markham facilities

Remove poorly buried sections, decommission acceptably buried sections in situ

The options were assessed using the DECC Decommissioning Guidance Notes and Centrica comparative assessment guidelines. During the assessment process, evaluations were made principally on a qualitative basis using Centrica's established corporate risk assessment tables but also combined with deterministic values from the cost and energy usage estimates which were normalised to provide a consistent measure against all CA evaluation criteria.

The results of the assessment showed both options to be acceptable for the pipeline and umbilical, therefore, in alignment with the DECC guidance cost has been used as a differentiator. A potential cost saving of £1MM to £3MM has been identified in favour of the partial removal option.

Therefore, based upon Comparative Assessment the recommendation for decommissioning the Stamford pipeline and umbilical is partial removal; to remove the pipeline and umbilical ends near the Stamford well in the UK sector, and remove any unprotected pipeline and umbilical ends from inside the Markham 500m exclusion zone, leaving a small section of umbilical near the Markham Platform where it is protected by concrete mattresses. The flexible riser will be left for a potential re-use opportunity and will be decommissioned with the Markham facilities.


Figure 2-5: Selected option – partial removal

Table 2-3 is a summary of the proposed decommissioning option, for consistency and to ensure that the EIA directly aligns, this is as stated in the decommissioning programmes [58].

Table 2-3: Summary of decommissioning programmes

Selected Option Reason for Selection Proposed Decommissioning Solution

1. Topsides

n/a

2. Jacket(s)/Floating Facility (FPSO etc.)

n/a

3. Subsea Installation(s)

WHPS will be removed.

To remove all seabed structures and leave a clean seabed. To comply with OSPAR requirements.

WHPS will be removed from the seabed.

4. Pipelines, Flowlines & Umbilicals

Flexible riser will be re-used if possible.

Pipeline will be flushed and left buried in situ.

The pipeline is sufficiently buried and stable, posing no hazard to marine users. Minimal seabed disturbance, lower energy usage, reduced risk to personnel engaged in the activity.

The 6 inch pipeline will be left in situ, with the short end sections re-buried/cut to conform to recommendations by the National Federation of Fishermen’s Organisations. Surveys indicate pipeline will remain buried. Degradation will occur over a long period within seabed sediment, and this is not expected to represent a hazard to other users of the sea. The flexible riser will be unbolted at the pipeline and left with the Markham platform and re-used if possible.

Umbilical will be flushed and left buried in situ

The umbilical is sufficiently buried and stable, posing no hazard to marine users. Minimal seabed disturbance, lower energy usage, less risk to personnel engaged in the activity.

The umbilical will be left in situ with the short end sections cut and removed to conform to recommendations by the National Federation of Fishermen’s Organisations. Surveys indicate that the umbilical will remain buried. Degradation will occur over a long period within seabed sediment, and this is not expected to represent a hazard to other


Table 2-3: Summary of decommissioning programmes

Selected Option Reason for Selection Proposed Decommissioning Solution

users of the sea. The section of umbilical within the J-tube at the Markham platform will be fully removed, but within the NLCS a short section of the umbilical within the Markham platform 500m zone will remain where it is covered by protection mattresses and removed along with the Markham platform as part of future decommissioning activities.

5. Wells

Well will be plugged and abandoned to comply with HSE “Offshore Installations and Wells DCR 1996” and in accordance with accordance with OGUK Guidelines for the Suspension and Abandonment of Wells.

Meets DECC and HSE regulatory requirements.

The Stamford well will be plugged and abandoned using a drill rig. A Master Application Template (MAT) and the supporting Subsidiary Application Templates (SAT) will be submitted in support of works carried out. A PON5 will also be submitted to DECC for application to abandon the well.

6. Drill Cuttings

No cuttings pile exists at Stamford.

Cuttings were widely dispersed and fall below OSPAR 2006/5 thresholds

n/a

7. Interdependencies

Mattresses and grout bags will be removed as part of the partial pipeline and umbilical removal activities.

Stamford

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Page 27

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device will be used to temporarily fluidize the sea floor supporting the pipeline. This will allow the pipeline to ‘sink’ under its own weight and be buried by a natural backfill process.

Sections of the pipeline that are ‘sufficiently’ buried in the seabed or covered with rock will be left in situ.

At the Markham Platform the pipeline will be unbolted for reuse and left in situ. The flexible riser at the platform will be capped and remain filled with inhibited water. It will be repositioned in preparation for potential reuse opportunity.

2.3.4 ‘Partial Removal’ of the control umbilical

The methanol and corrosion inhibitor cores of the umbilical will be flushed to remove the content. The control umbilical will be disconnected from the tree at the wellhead and cut after the mattresses at the platform end. The sections of the umbilical that are ‘insufficiently’ buried (i.e. un-trenched or transitionally trenched) at both the wellhead and the platform (approximately 162m) will be cut, and removed and recovered for recycling onshore.

The section of umbilical within the J tube on the platform (91m) will be lowered to the seabed and recovered for recycling or landfill on shore. The section under the mattresses will remain on the seabed for decommissioning at the same time as the Markham platform.

2.4 Summary

2.4.1 General (and common to all elements below)

The vessels used will include Dive Support Vessel (DSV), standby vessels / guard vessels, ROVSV and survey vessels. The duration includes transit to/from field and the operations in the field. It should be noted that the vessels will be used at both the well end and at the Markham Platform. Therefore, the associated impacts are dispersed over the area, 7.5km apart, rather than at a single location. The pipeline and umbilical decommissioning will be undertaken at the same time, but the vessel use has been presented separately to be consistent with the comparative assessment and decommissioning programmes.

An estimate of duration and fuel usage of each vessel for the pipeline and umbilical

decommissioning is shown in Table 2-4 and

, respectively. Estimates of fuel use have been based on Institute of Petroleum Guidelines [87]. It should be noted that these are worst case estimates. The duration of vessel use will continue to be optimised up to the time the decommissioning works takes place, therefore the actual duration are likely to be lower (in alignment with commitments made in this EIA report).

Table 2-4: Vessel requirements for pipeline decommissioning

Vessel Fuel usage (Tonnes)

Type Duration (Days)

DSV 31 558

Standby 31 24.8

ROVSV 7 126

Table 2-5: Vessel requirements for umbilical decommissioning


Legacy Surveys Vessels 9 13.5

2.4.2 Removal of the WHPS

Cutting or retracting of the WHPS legs and lifting of the structure to surface (DSV for less than 1 day).

2.4.3 Pipeline (‘Partial removal’) and control umbilical (‘Partial removal’)

Cleaning - Displacement of content of umbilical cores with water (with the exception of Aqua-Glycol 24F and AQUALINK 300F VER2);

Cleaning - Pigging and flushing of pipeline to leave the pipeline filled with treated seawater;

Disconnection of the pipeline spool pieces from the wellhead and from flexible pipeline after the mattresses at the platform;

Excavating local seabed to gain access for cutting the pipeline and umbilical at the Stamford well end;

Water jetting of insufficiently buried pipeline sections to facilitate burial (contingency only – removal and recovery preferred);

Cutting of the pipeline and the control umbilical;

Lifting of disconnected spool pieces and cut pipeline lengths;

Lifting cut lengths of control umbilical; and,

Repositioning of flexible riser

2.4.4 Removal of the pipeline and control umbilical protection

Lifting of concrete mattresses and grout bags.

2.4.5 Legacy survey vessel

Following decommissioning the pipeline and umbilical will remain in the seabed. Periodic surveys will check the burial status and confirm that the pipeline and umbilical do not present a hazard to marine users.

It has been estimated that the survey of the pipeline will require a day or two. After decommissioning has been completed, two pipeline status surveys and two environmental surveys will be done with the findings being sent to DECC. The frequency of these surveys will be agreed with DECC. Survey vessels are dynamically positioned. Survey durations include

Table 2-5: Vessel requirements for umbilical decommissioning

Vessel Fuel usage (Tonnes)

Type Duration (Days)

Reel 5.5 99

Standby 5.5 4.4

Legacy Surveys Vessels 9 13.5


mobilisations; but it is recognised that these are likely to be shared as the surveys will be part of larger survey campaigns.


3 ENVIRONMENTAL BASELINE

This section of the EIA report describes the environmental setting of the Stamford facilities. The sensitivities in the location and the surrounding area that may be affected by the proposed decommissioning works are identified. The information will be used to assess the level of impact that the aspects (activities with the potential to impact the environment) have on the environment.

A number of surveys have been undertaken in the vicinity of Stamford, both prior to and post development of Stamford. The surveys inform the environmental baseline and the impact assessment.

Gardline Environmental Limited (2007). Multifield survey campaign 2007. UKCS 47/8, 47/9 and 49/10. June 2007. Environmental Baseline Report. RPS Energy for Venture. [20]

Fugro EMU Limited (2014a) Stamford Well and Stamford to J6A 6” Gas Pipeline and 5” Umbilical, Pre-Decommissioning Survey: UKCS Blocks 49/10c, 49/10b and NLCS Block J6: Volume 1 of 2: Habitat Assessment Report. [21]

Fugro EMU Limited (2014b) Stamford Well and Stamford to J6A 6” Gas Pipeline and 5” Umbilical UKCS Blocks 49/10c, 49/10b and NLCS Block J6: Volume 2 of 2: Pre-Decommissioning Environmental Survey. [22]

The aim of the pre-decommissioning environmental survey (carried out on 24th - 25th April 2014 [21]) was to use sampling locations close to those locations used for the predevelopment 2007 survey [20]. The 2007 stations themselves were positioned around the Stamford Well, observing an exclusion zone of 250m and staggered either side of the Stamford to Markham Platform 6" Gas Pipeline and 5” Umbilical route at 1km intervals (with an exclusion zone of 200m).

The pre-decommissioning survey area covered an area of 8km x 500m (with an additional area of 250m x 600m surveyed to the north northwest of the Stamford well) with coverage including analogue geophysical data acquisition, environmental sampling and habitat assessments.

The acoustic survey was along the pipeline / umbilical route corridor, around the Markham Platform and around the wellhead.

Drop-down camera operations were recorded at eight stations (seven at the well and one and at a reference point 1 km north northeast of the well). Grab samples were gained at two of these eight stations (one at the well and one at a reference point 1 km north northeast of the well), Figure 3-1, [21].

Supplementary data to characterise the area around the Markham Platform including sediment data was taken from:

FSLTD (2013) ST-1 decommissioning survey, UKCS Block 49/5A, Volumes 1 & 2. Environmental Habitat Assessment with Herring Spawning Ground Assessment [23], (Fugro Survey Ltd. No. 130019.1V1.2) and

Environmental Baseline Report, [24], (Fugro Survey Ltd. No. 130019.1V2.0) plus Fugro EMU Limited (2014) Centrica Grove North East Environmental Survey [25].

3.1 Physical and chemical environment

This section provides information on the physical and chemical characteristics of the environment at and around the Stamford facilities. The physical environment in which Stamford lies is typical of the southern North Sea region.


3.1.1 Bathymetry

The bathymetric data collected from the April 2014 pre-decommissioning survey was obtained using hull-mounted single and multi-beam echo sounders (22). The information collected included side scan sonar and bathymetric data and was collected at both the well location and along the pipeline route corridor. Figure 3-1 shows the sample locations at the 8 no. stations.

The seabed depth in the area of the survey ranged between ~29m and ~60m below lowest astronomical tide, with the shallowest areas identified as being in the south west and north east of the survey area.

A broad channel (Markham’s Hole) runs between Stamford and the Markham Platform, this forms an elongated crest-like structure in the south west (well location) which coincides with the minimum depth record (29m). The maximum depth (60m) was recorded adjacent to this channel. A second raised bathymetric feature is present in the north east (Markham Platform). The gradient across the study area is on average generally low (<1°), however a gradient of up to 19° was recorded in the south west on the side of the central channel (Figure 3-1).

Multiple trawl scars were observed across the survey area, the presence of four possible boulders with a height of up to 1m were also observed within the survey area [21].

The bathymetry along the ST-1 and Grove pipeline routes is also shown in (Figure 3-1).

Stamfor

*

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* Current Survey

ning Environmen

Fig

y refers to the St

ntal Impact Asse

gure 3-1: Bathym

tamford 2014 pr

essment

metry survey res

re-decommission

sults and sample

ning survey

e locations [22]

Pagge 33

Stamford

3.1.2 C

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Page 34

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Figure 3-3: Mean wind direction for the Stamford area [3]

3.1.4 Sea temperatures and salinity

Temperatures within the southern North Sea vary seasonally, ranging from 5ºC in the winter months and up to 15ºC in the summer months at both the seabed and surface [28].

The salinity of the North Sea and at the Stamford location itself remains constant throughout the year. The conditions are formed from the mixing of surface water which is terrestrial in origin and the marine influxes from the Atlantic and English Channel. The salinity at the seabed and surface has been measured as 34.6% and 34.75% respectively [28].

3.1.5 Seabed characteristic, sediments and types

Seabed sediments are composed of mineral and organic particles, which occur commonly in the form of mud, sand or gravel and are dispersed by processes driven by wind, tides and contrasts in water density. The nature of the local seabed sediments also plays an important role in the determination of flora and fauna. Seabed sediments provide a habitat and food source for benthic infauna [3]. Within the North Sea sediments consist mainly of sand, gravel and muds [29].

The area itself is mainly smooth, apart from the channel in the south west and raised feature in the north east. The 2014 survey [22] identified two main sediment types; silty fine sand with occasional shell fragments which dominate the north east of the well and along the pipeline route corridor; and gravelly sand with the occasional small cobbles and boulders found south of the well.

The sediment classification from survey data for ST_01 and ST_014 [21] is provided in Table 3-1.

Stamford

These cclassifica

SurveyYear

2007

2014

The survecover to sandy claend of the

At the Stcobbles aof the weeast of thThe sediStamfordthe under

A numbeareas wedefined uthan 256 of cobbleand 40%criteria. E

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3.1.5.1

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Table 3-1:

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ST_01

ST_14

ST_01

ST_14

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Page 36

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gravel, pebbles and cobbles. As with the composition of sediments at the four stations above, were also characterised as ‘circalittoral mixed sediments’; however compared to the previous four sample locations, there was a lower proportion of lithic sediments.

The mixed sediment associated with this biotope complex provides an environment suited to mobile and sessile fauna.

Key: Plate 1: Station 01, Still 01 – Muddy fine sand with faunal burrows and bioturbation Plate 2: Station 01, Still 11 – Muddy fine sand with faunal burrows and bioturbation Plate 3: Station 14, Still 03 – Muddy fine sand with faunal burrows and bioturbation Plate 4: Station 14, Still 07 – Muddy fine sand with faunal burrows and bioturbation Plate 5: Station 01_FB – Sieved grab sample showing infaunal polychaetes and brittle stars (Ophuiroidea) Plate 6: Station 14_FB – Sieved grab sample showing heart urchin (Echinocardiumcordatum) and polychaetes

Figure 3-4: Seabed and grab photographs [21]

3.1.6 Seabed chemistry

The chemistry (composition of hydrocarbons and metals) of the seabed in and around the Stamford facilities is shown in Table 3-2 and Table 3-4. Chemical analysis of sediment samples was undertaken for both the 2007 and 2014 surveys ([20] & [22]).


The decommissioning activities are at the well and the Markham Platform, so the analysis from these locations is presented. The 2014 grab samples were targeted on the same locations as the 2007 grab samples so that the results can be directly compared (see Figure 3-1 for locations and Table 3-2 for results). The sample locations at the well are:

WENV (2007 survey) and 1 ST-01 (2014 survey)

Samples were taken from approximately 1km north northwest of the well, providing background data

WENV 7 (2007 survey) and ST-14 (2014 survey)

Directly comparable samples were not obtained at the Markham Platform, however the following two sample points were taken from approximately 200m of each other and presented in Table 3-3.

PENV7 (2007 survey) and Station 13 (ST-1 2013 survey)

The results are compared in Table 3-2 (samples at well) and Table 3-3 (Markham Platform) to Southern North Sea Mean data [68] and NOAA effects Range Low data [69].

Table 3-2: Summary of contaminant concentrations at well head (20 & 22)

Source TOM TOC THC PAH Zn Cd Hg Ba Pb Fe

% % µg.g-1 4-6 Ring

Ratio µg.g-1 µg.g-1 µg.g-1 µg.g-1 µg.g-1 µg.g-1

WENV 7– 2007 survey

1.4 0.6 6.3 1.88 25 0.1 0.03 350 13 12000

ST-14 – 2014 survey

1.99 0.5 4.4 0.68 32.3 0.2 0.02 335 14.6 14400

Change +/-ve 0.59 -0.1 -1.9 -1.2 7.3 0.1 -0.01 -15 1.6 2400

% Change 42 -17 -30 -64 29 100 -33 -4 12 20

WENV 1– 2007 survey

1.6 0.4 7 1.84 200 0.1 <0.07 380 16 -

ST-01– 2014 survey

1.85 0.52 2.7 0.71 37.7 0.3 0.03 335 13.5 14400

Change +/-ve 0.25 0.12 -4.3 -1.13 -162.3 0.2 0 -45 -2.5 N/A

% Change 15.625 30 -61.4 -61.4 -81.1 200 0 -11.8 -15.6 N/A

UKOOA Mean 1.2 - 4.3 0.87 21.8 0.5 0.03 218.4 12.7 -

NOAA ERL - - - - 150 1.2 0.15 - 46.7 -


Table 3-3: Summary of contaminant concentrations at Markham Platform and typically found in southern North Sea surface sediments [20] & [22]

Source TOM TOC THC PAH Zn Cd Hg Ba Pb Fe

% % µg.g-1 4-6 Ring

Ratio µg.g-1 µg.g-1 µg.g-1 µg.g-1 µg.g-1 µg.g-1

PENV 7 (pipeline) 2007 survey

0.7 0.2 2.4 1.71 10 <0.04 <0.02 210 10 9600

Station 13 – ST-1 2013 survey

0.75 0.3 1.2 1.1 34.8 0.5 <0.01 612 12.5 21300

Change +/-ve 0.05 0.1 -1.2 -0.61 24.8 N/C N/C 402 2.5 11700

% Change 7 50 -50 -36 248 N/C 0 191 25 N/A

UKOOA Mean 1.2 - 4.3 0.87 21.8 0.5 0.03 218.4 12.7 -

NOAA ERL - - - - 150 1.2 0.15 - 46.7 -

N.B. these are not normalised concentrations

The three colours used in the table show the following:

Green – The green cells show the locations where the concentration has decreased between the 2007 and 2014 survey. This is indicative of environment recovering.

Orange – The orange cells show the locations where the 2014 sediment analysis, even after improvement from 2007 exceed the UKOOA mean or NOAA effects range – lower.

Red - The red cells show the locations where there has been an increase in concentration between 2007 and 2014 and the values exceed the UKOOA mean or NOAA effects range – lower.

Broadly the results show a decrease in concentrations between the 2007 and the 2014 surveys, with few of the concentrations exceeding benchmark data [68] and [69].

Although levels of organic content were generally higher in 2014 than recorded at directly comparable 2007 stations, current levels of TOM and TOC are thought to be representative of regional background levels; they are not elevated in a wider spatial context, and no substantial increase has occurred following the 2007 Stamford baseline survey.

A slight reduction in barium has occurred since 2007 at the well end, but an increase at the Markham Platform. The levels, although not indicative of significant contamination, do indicate that low-level effects of drilling activities may persist in the Stamford area.

The 2014 survey (22) indicates that iron concentrations are moderately high and have shown an increase when compared to 2007 data. However, when compared with the data for the wider area current concentrations are not considered to be substantially elevated above standard regional levels.

The measured concentration of lead increased between the 2007 and 2014 surveys at the well end, the increase puts the level above the UKOOA mean, but below of the NOOA ERL. The difference between the two results is relatively small (12%). A similar trend was identified for zinc, with the difference being larger at 30%, but still below the NOOA ERL.

No heavy or trace metals exceeded sediment quality guidelines of NOOA ERL in the current survey, where they exist.


3.2 Biological environment

3.2.1 Plankton

Within the North Sea planktonic assemblages are influenced mainly by vertical mixing and the availability of light and nutrients (stratification) for growth [33]. Stamford is specifically influenced by this stratification from the north east Atlantic water, which in turn mixes with the North Sea water, although this is a gradual mix. During the winter months the rate of phytoplankton production decreases and increased concentrations of phosphorus, ammonia, nitrogen and silicate can be recorded as these are not used up during the production of phytoplankton. However, the rate of primary production increases significantly during the spring months, which is subsequently followed in August by a smaller peak in abundance of phytoplankton [34].

Within the Stamford area, the presence of the temperate shelf sea species of plankton is predominant, with these species also being dominant across the southern North Sea; the two most common species being Ceratiumfusus and Ceratiumfurca. The population of diatoms is also significant and includes: Chaeotoceros (Hyalochaere and Phaeocerus) [33]. However, these have been notably recorded as decreasing over time (from 1990 to 2000) dinoflagellates becoming more abundant, due to the increased inflow into the North Sea [28].

Zooplankton, specifically Para-psuedocalanus spp, is mainly composed of small copepods.

The abundance of smaller intermediate and neritic copepods are also present within the Stamford survey area which includes Temoralongicornis and Acartia spp. Other abundant taxa include Evadne spp, Oithonaspp and Podon spp. Planktonic organisms, primarily copepods compose the main food resource for many commercial fish species [36].

3.2.2 Benthos

The organisms which live on or near the seabed are called benthos. Infaunal species are vulnerable to external influences which alter the biological, physical or chemical community of the sediment. These species are largely sedentary and unable to adapt to unfavourable conditions.

The results from the benthic survey show the site and pipeline route to have two distinct groups of stations with many of the taxa found to be abundant at some stations, but absent or only present in small numbers at others. The variations in community types has been attributed to the sediment along areas of the pipeline route having proportions of fine particles with others, including the well having coarser sediment [3].

Due to the mobility of sediments in this area, species which survive here are expected to be adaptable to this environment, which includes infaunal species such as polychaetes (marine worms), the heart urchin, sea potato, and members of the molluscs genus. The presence of larger animals, which utilise the sediment surface include the starfish, swimming crabs and hermit crabs. Two of the photographs taken from stations 08 and 13 during the pre-decommissioning survey are provided in Figure 3-5 and Figure 3-6.

In fine and sandy sediments, benthic communities are typically dominated by infaunal taxa, making habitat classifications based upon seabed photography alone problematic. Photographic analysis suggested that epifauna were extremely sparse within this biotope, although infauna appeared to be relatively rich and abundant. Numerous infaunal burrows were observed from seabed photography data and sieved grab sample analysis revealed an assemblage of sea potatos, brittle stars, and polychaete worms. The survey indicated the presence of Ross worm (Sabellaria spinulosa), a species of potential conservation importance.

Stamford

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Page 41

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Page 42

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Table 3-4: Seabird vulnerability to oil pollution in the vicinity of the proposed development [39]

Block Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average

49/4

49/5

49/9

49/10

49/14

49/15

Table 3-4 shows that the most sensitive time of year for seabirds in the Stamford area (49/10) is during November and December. The vulnerability of the seabirds to oil spills during this time is very high. During the remainder of the year, vulnerability ranges from low to high, Jan – May, July and October high sensitivity, June and September moderate sensitivity and August low sensitivity. This corresponds with the period when young guillemots and little auks leave the coastal colonies and migrate to offshore waters and fully grown birds undergo a moult and are flightless, leaving them particularly vulnerable to surface pollution.

3.2.4 Fin fish and shellfish

The fisheries of the North Sea can be classified into categories according to their commercial use: pelagic (mid-water fish); demersal (near-bottom dwelling fish); and shellfish. The fish populations in the area of Stamford are characterised by species common to the Southern North Sea. Pelagic species are dominated by herring and mackerel while demersal stocks are characterised by cod and whiting [40]. Fish are known to congregate around offshore platforms [4], which provide a habitat for certain species.

Spawning regions for a variety of fish species also occur in the Stamford region and the area also supports nursery grounds for both pelagic and demersal species. Block 49/10c, is a spawning ground for mackerel, herring, whiting, sprat, nephrops, sandeel, cod and plaice.

Additionally, the area is a nursery ground for mackerel, herring, whiting, plaice, sprat, nephrops, anglerfish, cod, spurdog and tope shark (Figure 3-7).

Tolerance to installation activities, discharges and accidental spills is dependent on the time of year. The most sensitive period to offshore activities is from the beginning of the year through to autumn, when most species spawn. This seasonal and temporal vulnerability needs to be considered when planning offshore activities as fish can be exposed to aqueous discharges and may accumulate toxic chemicals in their body tissues. Demersal spawners and shellfish are particularly vulnerable to hydrocarbon spills (where hydrocarbons can partition to the sediment), as they feed on contaminated benthic organisms.

Very high sensitivity High sensitivity Moderate sensitivity Low sensitivity


Spawning ground for Nephrops, Sprat and Place

Spawning ground for Herring, Cod and Mackerel

Nursery ground for Nephrops, Sprat and Whiting

Figure 3-7: The spawning and nursery grounds of some fish species surrounding Stamford [3]

Note: Geographical data is not available for all species


3.2.5 Annex I Habitats

Figure 3-8 shows the designated areas in the vicinity of Stamford. Currently in UK offshore waters there are no SACs, one candidate Special Areas of Conservation (cSACs) and nineteen SCIs. In addition, there is an on-going process of SAC identification in UK offshore waters. The JNCC has identified areas where additional SACs may be sited, following further survey work or analysis of data gathered through surveys already conducted. These areas are termed Areas of Search (AoS). There are currently three AoS in UK offshore waters [42]. AoS are based upon the best available evidence of the location of Annex I features of sandbanks slightly covered by seawater at all times, reefs and submarine structures made by leaking gases (Table 3-5). At present within the UK offshore waters there are four habitats from Annex I and four species from Annex II of the Habitats Directive which are being considered as being identified as SACs and are awaiting a decision [42].

Table 3-5: Annex I habitats considered for SAC selection in UK offshore waters [42]

Sandbanks that are slightly covered by seawater all the time

Reefs (bedrock, biogenic and stony)

o Bedrock reefs – made from continuous outcrops of bedrock which may be of various topographical shape (e.g. pinnacles, offshore banks);

o Stony reefs – these consist of aggregations of boulders and cobbles which may have some finer sediments in interstitial spaces (e.g. cobble and boulder reefs, iceberg ploughmarks); and

o Biogenic reefs – formed by cold-water corals (e.g. Lopheliapertusa) and the polychaete worm Sabellaria spinulosa.

Submarine structures made by leaking gases

Submerged or partially submerged sea caves.

Habitats within the Stamford survey area, which displayed potential evidence for conservation significance included ‘sandbanks which are slightly covered by sea water all the time’ and ‘reefs’ (particular stony reefs, details of which are present in Section 3.1.6.1) and those formed by the Ross worm, Sabellaria spinulosa. The 2007 and 2014 surveys ([20], [21] and [22]) did not identify any species or habitats which would be categorised under the EC Habitats Directive as being of conservation significance.

Stamford is located over 26km north east from the North Norfolk Sandbanks and Saturn Reef SAC. The Cleaverbank Special Area of Conservation is located just over 1km northeast from the Markham Platform and is within the Netherlands sector. The area is the only site in the Netherlands sector of the North Sea where considerable quantities of gravel lie on the surface and larger cobbles with a specific covering of calcareous red algae also occur. It is potentially important for the propagation of fish species such as spotted ray and herring which both require hard substrates.

The Marine and Coastal Access Act (2009) [4] created a new type of Marine Protected Area (MPA), called a Marine Conservation Zone (MCZ). The nearest recommended MCZ is the NG7 Markham’s Triangle, which covers an area of approximately 200km2 and is located in Block 49/5 adjacent to Block 49/10 .The designation of Markham’s Triangle (6km north from the Markham Platform) is currently awaiting a decision on designation as a Marine Conservation Zone. The water depth in the MCZ ranges from 30-50m. The seafloor is coarse sediment and sand with small patches of rock and gravel, which supports a benthic community, notably including sandeels which are a key food source for many marine mammals.

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Page 46

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Annex II of the Habitats Directive (92/43EEC) [31]; All cetacean species are listed in Annex II of the Convention on International Trade in

Endangered Species of Wild Fauna and Flora [43]; Appendix II of the Bern Convention Annex [44]; Appendix IV of the EC Habitats Directive as species of European Community interest and in

need of strict protection [31]; and Schedule 5 of the Wildlife and Countryside Act 1981 [45].

Cetaceans

The presence of cetaceans in the North Sea include the Atlantic white-sided dolphin, harbour porpoise, minke whale and white-beaked dolphin, all of which have been recorded as present around the surrounding area of Stamford. The most frequently encountered species within the UK waters is the harbour porpoise [3]. According to the UK Digital Marine Atlas Project [28] the distribution of these species in terms of sightings within the area around the Stamford facilities is as follows: harbour porpoise (regular – high number of sightings in June - September), minke whale (scarce/casual), white beaked dolphin (occasional) and white sided dolphin (scarce/casual/occasional). An overview of the seasonal occurrences of each species is given in Table 3-6.

Table 3-6: Sightings of cetaceans in the area surrounding Stamford [28].

Species Month

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average

Harbour porpoise

Minke whale

White beaked dolphin

White sided dolphin

Cetaceans, and specifically the porpoise, are particularly sensitive to anthropogenic noise that is likely to be produced from shipping, operation of noisy equipment, oil-platforms and offshore wind farms, all of which have the potential to affect the distribution and behaviour [46]. Vital functions performed by many mammals such as feeding, resting are performed on a dial cycle. If this cycle is disrupted (usually over a sustained period, rather than single instances) then this increases the possibility of an effect on growth, birth and death rates of that mammal [46].

High Moderate Low


Pinnipeds

Common seals are not usually recorded more than 60km from shore and given the location of Stamford, 140km from the English coastline, it is unlikely for the presence of the common seals. Both grey and common seals are present in the southern North Sea. Distribution data on grey seals suggest that there is the possibility for grey seals to be present at the well location, however the length of time spent within this area is not expected to be long. Pupping and moulting seasons occur from May to August, during which time seals will be ashore more often than at other times of the year.

3.3 Socioeconomic environment

This section outlines the wider context of the impact that the decommissioning of the Stamford facilities can have on socioeconomic activities including the opportunities for employment.

3.3.1 Other Oil and Gas

Stamford is tied back to the Markham Platform, which forms a hub for other fields in the area. Figure 3-9 shows the other oil and gas infrastructure in the vicinity of Stamford.

Figure 3-9 Oil and gas infrastructure in the vicinity of Stamford

3.3.2 Shipping

Stamford is within 10 nautical miles of 12 different shipping routes, where a total of 5,541 ships are typically recorded per year (15-16 per day) [3], and is close to the Traffic Separation Scheme (TSS): a traffic-management route-system is established and under the responsibility of the


International Maritime Organization. The traffic-lanes (or clearways) indicate the general direction of the ships in that zone; ships navigating within a TSS all sail in the same indicated direction or if they cross the lane they must do so at an angle as close to 90 degrees as possible. Planned vessel movements associated with decommissioning operations should take account of the TSS and vessels using them.

3.3.3 Wind farms

Stamford is also located within the Hornsea windfarm licenced area (Figure 3-10). There is currently no wind farm developed or with planning permission for the Stamford area which lies to the eastern boundary of the windfarm area.

Figure 3-10: Location of wind farm areas in relation to Stamford [3]

3.3.4 Aggregate extraction

There are no areas within the Stamford area that have been identified as being licensed for marine extraction [48].

3.3.5 Ministry of Defence (MOD)

Stamford is not located within an area known for activity by the MOD.


3.3.6 Commercial fishing industry

One of the main areas of potential adverse socio-economic impacts associated with the offshore oil and gas industry is in relation to fishing activities. During decommissioning, vessel movements may be restricted and the state of the seabed post-decommissioning will affect fishing grounds. Knowledge of fishing activities and the location of the major fishing grounds is therefore an important consideration when evaluating any potential environmental impacts from decommissioning operations.

In terms of marine ecosystems, the International Council for the Exploration of the Sea (ICES) is the primary source of scientific advice to the governments and international regulatory bodies that manage the North Atlantic Ocean and adjacent seas. For management purposes ICES collates fisheries information for area units termed ICES rectangles measuring 30nm by 30nm. Each ICES rectangle covers approximately one half of one quadrant i.e. 15 licence blocks. The importance of an area to the fishing industry is assessed by measuring the fishing effort which may be defined as the number of days (time) x fleet capacity (tonnage and engine power). Due to the requirement by UK fishermen to report catch information such as total landings (includes species type and tonnage of each), and location of hauls and catch method (type of gear/duration of fishing), it is possible to get an indication of the value of an area (ICES rectangle) to the UK fishing industry. It should be noted, however, that fishing activity may not be uniformly distributed over the whole area of the ICES rectangle. Stamford lies in ICES rectangle 36F2.

3.3.7 Fishing Effort

The UK fishing effort within this area varies throughout the year and annually can be considered low with an average fishing effort of 140 days per annum (2010 – 2013). Approximately 0.07 % of total UK landings between 2010 and 2013 were taken from the area Table 3-7 [32].

Table 3-7: Fishing effort by UK fishing fleet in ICES rectangle 36F2 compared with UK total [32]

Year Total Fishing Effort by UK Fishing Fleet (days)

UK Total 36F2 36F2 as % of UK

2010 205,100 182 0.09

2011 188,400 155 0.08

2012 185,200 76 0.04

2013 183,400 147 0.08

Average over 2010 - 2013 140 0.07

Note these data are based on reported landings from ICES rectangles within which more than five UK vessels measuring over 10m were active. In those ICES rectangles where <5 vessels were active the information is considered disclosure and is therefore not available.

3.3.8 Fish Landings

The quantity of landings by UK vessels in ICES rectangle 36F2 is shown Table 3-8. The area is


targeted primarily for demersal species as shown in Figure 3-11. The data suggest that ICES rectangle 36F2 is of relatively low value to the UK fishing industry.

Table 3-8: Total landings by UK fishing fleet in ICES rectangle 36F2 compared with UK total [32]

Year Total Landings by UK Fishing Fleet (te)

UK Total 36F2 36F2 as % of UK

2010 632,900 496 0.08

2011 622,600 1,244 0.20

2012 679,000 962 0.14

2013 640,900 448 0.07

Note these data are based on reported landings from ICES rectangles within which more than five UK vessels measuring over 10m were active. In those ICES rectangles where <5 vessels were active the information is considered disclosure and is therefore not available.

Figure 3-11: Live catches within ICES rectangle 36F2 by species type [32].

Non-UK vessels also target fish in the area. Stamford lies close to the boundary between ICES subdivisions IVb and IVc, therefore data for both areas are considered. ICES catch statistics show that the main nations fishing in ICES Divisions IVb and IVc in 2012 were Denmark, Norway, Netherlands, UK and Germany (Figure 3-12, [32]).

Figure 3-13 shows that the landings of major fish stocks in the UK North Sea are shared by several EU nations [32].


Figure 3-12: Fish catch by EU member state in ICES Divisions IVb and IVc in 2012 [32]

Figure 3-13: Share of landings in the UK North Sea by EU member states in 2013 [32]


3.3.9 Summary of environmental sensitivities

Table 3-9 summarises the environmental sensitivities in the vicinity of Stamford.

Table 3-9: Key environmental sensitivities

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecHabitats Directive: Annex I Habitats Surveys did not identify any species or habitats which would be categorised under the EC Habitats Directive as being of conservation significance. Marine conservation areas (SAC, SCI and a potential MPA) exist in the UKCS to the east, north-west and north of the facilities. Some of them have qualifying features that meet those stated in Annex I. Habitats Directive: Annex II Species Of the four Annex II species (harbour porpoise, minke whale, white beaked dolphin and white sided dolphin) that are listed as occurring in the UK offshore waters, only the harbour porpoise has been reported as being ‘regularly’ sighted in the area surrounding the Stamford facilities. Benthic Fauna Benthic communities around Stamford are similar to those found throughout the surrounding area of the North Sea. Plankton During summer there is a smaller peak in abundance of phytoplankton. However during the winter months the rate of phytoplankton production decreases due to increased ionic concentrations. Finfish and Shellfish The Stamford area is a spawning ground for mackerel, herring, whiting, sprat, nephrops, sandeel, cod and plaice, and a nursery ground for mackerel, herring, whiting, plaice, sprat, nephrops, anglerfish, cod, spurdog and tope shark. The most sensitive period with regards to offshore activities is the beginning of the year through to autumn, when most species spawn. The spawning of the species listed above occurs throughout the year. Marine Mammals The presence of marine mammals in the North Sea include the Atlantic white-sided dolphin, harbour porpoise, minke whale and white-beaked dolphin all of which have been recorded as present around the surrounding area of Stamford. The distribution in terms of sightings within the area around the Stamford facilities is as follows: harbour porpoise (regular), minke whale (scarce/casual), white beaked dolphin (occasional) and white sided dolphin (scarce/casual/occasional) Seabirds The vulnerability of seabirds from oil pollution in November and December is elevated compared to the other months in the year (albeit that there is high vulnerability during the rest of the year), therefore as there is the potential for discharge to sea from vessels during the decommissioning activities, any operations would be subject to additional careful planning around Q4. Fisheries This area of the southern North Sea is of low to moderate commercial fishing value. For all gears combined, effort tends to be greatest during the months of January, August, October, November and December. Effort in these months’ accounts for 65% of the total number of days fished (2010-2013 data). Shipping and wind farms The majority of shipping volume comprises industry shipping activity and cargo voyages. Stamford is within a licenced wind farm area. Very high sensitivity Low sensitivity High sensitivity Not surveyed / No data available Moderate sensitivity

Note: Sensitivities as listed in the above Table are not comparable with each other as they are indicative of the varying levels of sensitivity throughout the year, but not equal in sensitivity.


4 EIA METHODOLOGY

4.1 Overview

The EIA process identifies the environmental impacts of a project from activities (both planned activities and unplanned events) and aims to prevent, reduce and offset any adverse impacts identified. Planned activities and unplanned events likely to affect the environment (aspects) or other users of the environment are first identified, then assessed to define the level of impact they could cause. Where necessary, project specific control and / or mitigation measures in addition to the industry standard, legislative and prescriptive controls and mitigation measures are identified in order to reduce any impacts to as low as reasonably practicable (ALARP) in line with the philosophy of the Centrica Environmental Policy.

4.2 Impacts from planned activities

The environmental impact assessment matrix is used to assess the planned impacts before and after control/mitigation measures. The controls and mitigations then form the basis for the Environmental Management Plan (EMP) thereby providing a systematic approach to controlling the impacts on, and interactions with, the environment.

4.2.1 Duration/frequency

A consideration of both the duration and frequency of each aspect (impact causing activity) allows a numerical score of between one and five to be awarded (Table 4-1).

Table 4-1: Duration / frequency of an aspect

Planned aspect Category

One to many years Long term continuous

5

One month to a year Short term continuous or intermittent over a long duration

4

One week to a month Short term intermittent

3

One day to a week One off over a few weeks

2

Less than a day One off over a day

1


4.2.2 Consequence/severity

The consequence/severity of each aspect is also rated on a scale of one to five as shown in Table 4-2. Where consequence/severity appears to fall within two categories, the higher category should be selected to provide a worst case for the purposes of the assessment.

Table 4-2: Consequence / severity of an environmental aspect

Level Definition

Catastrophic (5) Change in ecosystem (land, air or water) leading to long-term (greater than 10 years) damage and impact on associated species with poor potential for recovery to the area or species.

The thresholds for impact on species / features / environmental area are:

2 hectares of more littoral or sub-littoral zone or coastal benthic community, or the benthic community of any fish spawning area;

100 ha or more of the open sea benthic community;

10% of wide spread habitat area or population;

5% of a protected area;

1% of a protected species population impacted (not limited to mortality); for threatened or rare species appropriate statutory conservation organisations should be contacted to discuss the appropriate threshold;

soil, groundwater or aquifer contamination that would be regarded as contaminated by relevant authorities;

changes in air or water quality that would exceed relevant / applicable air quality standards.

Damage to an area of archaeological importance or nationally registered building such that there would be a loss of importance / de-registering if no remedial / restorative work is undertaken.

Long term substantial loss of private users or public finance (e.g long term loss of fishing grounds).

Major (4) Change in ecosystem (land, air or water) leading to medium-term (greater than 2 years) damage and impact on associated species with recovery likely between 2 and 10 years to the area or species.

The thresholds for impact on species /feature / environmental area are:

2 hectares or more of littoral or sub-littoral zone or coastal benthic community, or the benthic community of any fish spawning area;

100 ha or more of the open sea benthic community;

10 % of wide spread habitat area or population;

5 % of a protected area;

1 % of a protected species population impacted (not limited to mortality); for threatened or rare species appropriate statutory conservation organisations should be contacted to discuss the appropriate threshold.

soil, groundwater or aquifer contamination that would be regarded a contaminated by relevant authorities;

changes in air or water quality that would exceed relevant/applicable air


Table 4-2: Consequence / severity of an environmental aspect

Level Definition

quality standards;

Damage to an area of archaeological importance or a nationally registered building such that there would be a loss of integrity, not leading to de-registering /categorisation with a requirement for remedial / restorative work to be undertaken; and

Medium term, substantial loss or long term, minor loss of private users or public finance (e.g medium term loss of fishing grounds).

Severe (3) Change in ecosystem (land, air or water) leading to short-term damage and impact on associated species with recovery anticipated within 2 years to an area or species;

The thresholds for impact on species /feature / environmental area are:

Damage to an area of archaeological importance or nationally registered building with a requirement for minor remedial / restorative work to be undertaken; and

Possible short or medium term minor loss to private users or public finances (e.g short term loss of fishing grounds).

Moderate (2) Change is within scope of existing variability but potentially detectable.

Minor (1) Effects are unlikely to be noticed or detectable.

4.2.3 Combining duration/frequency and consequence/severity to establish significance of impact

The overall environmental impact posed by each aspect is assessed using the combination of the consequence/severity and duration/frequency scores in Table 4-3 to provide an indication of the significance of the impact associated with the aspect. There are three possible impact significance ratings corresponding to the coloured squares as shown in


Table 4-4: Environmental impact acceptance criteria

.

Table 4-3: Significance of environmental impact

Duration / frequency

1 2 3 4 5

Co

nse

qu

ence

/

Sev

eri

ty

5 High High High High High

4 Medium High High High High

3 Low Medium Medium Medium Medium

2 Low Low Low Medium Medium

1 Low Low Low Low Low


Table 4-4: Environmental impact acceptance criteria

Significance Acceptability Action required High Impacts are intolerable

in this region Controls and measures to reduce impact to ALARP (at least a medium) must be identified, documented, approved and implemented. The aspect should be reassessed once control measures have been identified.

Medium Impacts are tolerable Controls and measures to reduce impact to ALARP must be identified, documented, approved and implemented. The aspect should be reassessed once control measures have been identified.

Low Impacts are broadly acceptable

Controls measures are subject to continuous improvement

4.3 Impacts from unplanned events

As for Centrica’s impact assessment matrix, the Centrica risk assessment matrix for assessing the risk and severity of impact from unplanned events is a 5x5 Boston square. However rather than considering the duration/frequency of an event, the risk assessment matrix considers the likelihood of an event occurring and its impact to determine the risk.

4.3.1 Likelihood

A consideration of the likelihood of each aspect (impact causing activity) allows a numerical score of between one and five to be awarded (Table 4-5).

Table 4-5: Likelihood of an unplanned activity / event occurring

Descriptor Description Category

Very Likely Almost inevitable that an event would result 5

Likely Not certain to happen but an additional factor may result in an event

4

Possible Could happen when additional factors are present but otherwise unlikely to occur

3

Unlikely A rare combination of factors would be required for an event to occur

2

Very Unlikely An almost inconceivable combination of factors would be required for an event to occur

1

4.3.2 Severity / Consequence

The severity of each aspect resulting from an unplanned activity / event is also rated on a scale of one to five as shown in Table 4-2. Where the severity / consequence appears to fall within two categories, the higher category is selected to provide a worst case for the purposes of the assessment.


4.3.3 Combining likelihood and severity to establish risk from the unplanned event

The overall environmental risk posed by each aspect is assessed using the combination of the severity/consequence and probability/likelihood scores to provide an indication of the significance of the impact of the risk associated with the aspect (Table 4-6). There are three possible risk ratings corresponding to the coloured squares as shown in Table 4-7.

Table 4-6: Centrica Energy Upstream HSE Risk Assessment Matrix

Likelihood

1 2 3 4 5

Sev

eri

ty /

con

seq

uen

ce

5 Medium Medium High High High

4 Low Medium Medium High High

3 Low Low Medium Medium High

2 Low Low Low Medium High

1 Low Low Low Low Medium

Table 4-7: Risk acceptance criteria

Risk Level Acceptability Action Required

High HSE risks are intolerable at this level

Controls and measures to reduce impact to ALARP must be identified, documented, approved and implemented by the responsible L4 or higher leader.

Medium Risks are tolerable and managed to ALARP

Controls and measures to reduce impact to ALARP must be identified, documented, approved and implemented by the responsible leader.

Low Risks are broadly acceptable

Controls are subject to continuous improvement through implementation of the HSEQ MS and in light of changes such as technology improvements.

4.4 Assessment of Impacts, Risks and Control Measures

Using the information provided in Sections 2 and Section 3 and the criteria set out above an Environmental Management Workshop was held which includes the identification of the aspects and assessment of the environmental impact and risk of the aspects.

Those environmental aspects that are:

subject to regulatory control;

were found to pose a moderate or high risk to the environment; or

were recognised during the consultation phase as areas of public concern

are further assessed and described in Section 5.


5 ENVIRONMENTAL IMPACT ASSESSMENT

In this section the potential impacts have been identified and the control and mitigation measures designed to minimise these impacts to ALARP have been detailed.

An Environmental Management Workshop was held 24th September 2014 which identified the aspects and assessed the environmental impact and risk of the following:

Preparation of the facilities for decommissioning;

WHPS;

Subsea infrastructure removal;

General project operations;

Legacy requirements.

The environmental impacts considered are grouped into the following areas:

Energy use and atmospheric emissions

Underwater noise

Seabed disturbance

Discharges to sea

Releases to sea

Waste

Socioeconomic impacts

The EIA tables resulting from the Environmental Management Workshop are presented in Appendix A. All of the planned activities were considered to pose a low risk to the environment whilst the majority of the potential accidental events identified are also expected to be of a low environmental risk.

The risk of potentially damaging the wellhead once the WHPS has been removed was found to be medium prior to the identification of suitable additional mitigation measures. Mitigation measures were identified to lower the likelihood of the event so that the risk was subsequently reduced to low and ALARP.

This section is broken down into:

Source (aspects) and receptors

Impacts

Control and mitigation measures

Conclusions

5.1 Energy use and atmospheric emissions

This section of the EIA report provides an assessment of the estimated energy use and atmospheric emissions produced as a result of the activities to decommission the Stamford facilities. Control/mitigation measures intended to achieve optimum energy efficiency and reduce emissions to ALARP are also considered.


5.1.1 Sources and receptors

The Energy Institute (formerly the Institute of Petroleum) produced Guidelines for the Calculation of Estimates of Energy Use and Gaseous Emissions in the Decommissioning of Offshore Structures [87]. It informs this energy and emissions assessment. The main steps undertaken were:

Creation of a materials inventory;

Identification of all operations associated with decommissioning;

Calculation of energy use and atmospheric emissions.

Activities considered likely to consume energy and lead to emissions to atmosphere were identified for the decommissioning of the Stamford facilities.

a. Transportation and offshore operations

In field activities associated with the decommissioning of the Stamford facilities require vessels with the relevant capabilities, such as Diving Support Vessels (DSVs). The operation of the vessels comprises the most substantial consumption of energy and source of emissions to atmosphere from the decommissioning activities, for example they use dynamic positioning to hold station position and therefore engines are running all the time.

At the time of this assessment, specific vessels have not yet been reserved for the activities. However, the types of vessels required are well known and performance characteristics for typical example vessels of each class have been assumed for the purposes of estimating emissions to air and energy consumption.

Onshore transportation of recovered materials for reuse, processing, recycling or disposal to landfill is unlikely to be conducted on a scale that is expected to lead to significant additional emissions when considered in the wider context of general onshore transportation activities.

b. Recycling and recovery of materials

The onshore environment can be impacted more than the offshore environment due to the closer proximity sensitive receptors. Whilst onshore dismantling and manufacturing activities will consume energy, they will typically only generate indirect emissions (from power generation).

Recycling of recovered umbilical materials (predominantly steel, plastics and copper) will generate both indirect emissions and direct emissions from the secondary smelting process itself.

c. Manufacture of materials to replace those decommissioned In-situ

Whilst leaving the pipeline and umbilical in situ has no energy use and emissions to atmosphere, it could be considered that there is energy use and emissions from the manufacture of new, replacement of those materials ‘lost’. The consideration of these allows the energy use and emissions from the other activities to be put into context.

d. Estimates of emissions

The estimated energy use and emissions to air from the activities to decommission the pipeline in situ and removing the associated concrete mattresses and grout bags are presented in Table 5-1. It has been assumed that the pipeline ends will be removed for recycling.

Following decommissioning there will be a requirement for legacy surveys at appropriate


intervals, this will be required specifically to ensure that the pipeline will remain sufficiently buried to avoid risk to other users of the sea. Subsequently, there may be a requirement for additional works.

The principal emissions local to Stamford will be releases of combustion gases from vessel engines. Approximately 2% of the estimated energy usage and associated emissions is attributed to the manufacture of new materials to replace recyclable material left in situ. It should be noted that the emissions to atmosphere associated with this energy usage will comprise predominantly indirect emissions (i.e. from power generation), which will be assessed and permitted under legislation applicable to the site.

Table 5-1: Energy use and atmospheric emissions associated with pipeline decommissioning including associated mattresses and grout bags [51]

Decommissioning Aspect

Vessel Energy (GJ)

Emissions (Tonnes)

Type Days CO2 NOx SO2 CH4

Direct

Vessel use DSV 31 24,050 1,785 33 1.9 0.19

Standby 31 1,069 79 1 0.1 0.01

ROVSV 7 5,431 403 7 0.4 0.04

Legacy Surveys

9 582 43 1 0.1 0.01

Total 31,132 2,310 42 2.5 0.3

Indirect

Steel left in situ 437.2 Tonnes 10,930 811.95 60.32 4.48 0.33

Steel recovered (recycling)

6.8 Tonnes 61 4.53 0.34 0.03 0.00

Total 10,991 816.5 60.7 4.5 0.3

The estimated energy use and associated emissions for vessels conducting the removal of the end sections of the umbilical are provided below in Table 5-2.

The principal emissions local to Stamford will be releases of combustion gases from vessel engines. Approximately 2% of the energy consumption is attributable to the recovery of steel for recycling. As before, it should be noted that the energy usage and emissions to air associated with recycling will comprise predominantly indirect emissions (i.e., from power generation) which will be assessed and permitted under legislation applicable to the site.


Table 5-3 combines the direct and indirect energy use and emissions from the pipeline and umbilical activities to provide a summary of the overall energy use and emissions.

The WHPS will be recovered during the DSV activities the duration for which is accounted for pipeline and umbilical activities. The aspiration is for the WHPS to be re-used, therefore no energy use and associated emissions to atmosphere for recycling are presented.

5.1.2 Impacts on receptors

Energy use and emissions arise predominantly as a consequence of the combustion of fuel by vessels providing support for the decommissioning activities.

A proportion of the total emission (up to approximately 0.5%) is related to the recovery and onshore recycle or reuse of materials from the seabed. However, these emissions will be indirect (i.e. from power generation) and will be remote from Stamford. To put the emissions into context, 445,000 tonnes of CO2e were emitted from industry in Scotland in 2012 [70]. CO2 emissions from indirect sources from the Stamford decommissioning are equivalent to

Table 5-2: Energy use and atmospheric emissions from umbilical decommissioning including associated mattresses and grout bags [51]

Decommissioning Aspect

Vessel Energy (GJ)

Emissions (Tonnes)

Type Days CO2 NOx SO2 CH4

Direct

Vessel use

DSV 5.5 4,268 317 5.9 0.3 0.03

Standby 5.5 190 14 0.2 0.0 0.00

Legacy Surveys

9 581 43 1.0 0.1 0.01

Total 5,039 374 7.0 0.5 0.05

Indirect

Steel left in situ 70.1 Tonnes 1,753 130.2 2.4 0.15 0.015

Steel recovered (recycling)

4.9 Tonnes 44 3.3 0.1 0.00 0.000

Total 1,797 11.0 133.5 2.4 0.1

Table 5-3: Total Direct and Indirect energy use and atmospheric emissions.

Direct / Indirect Source Energy (GJ) Emissions (Tonnes)

CO2 NOx SO2 CH4

Direct Pipeline 31,132 2,310 42 2.5 0.30

Umbilical 5,039 374 7.0 0.5 0.05

Total 36,171 2,684 49 3.0 0.35

Indirect Pipeline 10,991 816 61 4.5 0.33

Umbilical 1,797 133 2.4 0.1 0.01

Total 12,788 950 95 6.7 0.34


0.05% of this value.

The power generators (source for indirect energy with associated emissions) are permitted under the Environmental Permitting regime (England) and the Pollution Prevention and Control regime (Scotland). The impact of the overall emissions from these activities will have already been assessed as low in accordance with other permitting regimes.

Similarly, energy requirements and the associated emissions from secondary steel smelting is also permitted under the Environmental Permitting regime (England) and the Pollution Prevention and Control regime (Scotland). For the permits to have been approved the impact of these direct emissions will also have already been assessed as acceptable in accordance with these other permitting regimes.

Recycling of recovered metals other than steel will not be undertaken on a scale that will lead to significant additional emissions (either indirect or direct) and may be discounted in the context of this assessment. Concrete recovered is likely to be crushed for reuse, anticipated to be a relatively low energy intensive activity.

The energy consumption associated with the decommissioning activities for Stamford is expected to lead to the emission of combustion gases including carbon dioxide (CO2), methane (CH4), nitrogen oxides (NOx), sulphur dioxide (SO2) and Volatile Organic Compounds (VOCs).

The direct impact of NOx, SO2 and VOC in the atmosphere is the formation of photochemical pollution in the presence of sunlight, comprising mainly low level ozone, but by-products may include nitric acid, sulphuric acid and nitrate-based particulate. The formation of acid and particulate may lead to a contribution to acid rainfall and the dry deposition of particulate. If such deposition occurs at sea, it is possible that the substances will dissolve in sea water but the level of deposition is unlikely to lead to any significant impacts on local sea water composition due to the relatively small amount when compared to emissions from other vessels. In addition, the ultimate fate of atmospheric emissions can often be difficult to predict owing to the dependence on variable weather (especially wind), over quite short timescales.

CO2 emissions contribute to greenhouse gas emissions and global warming impacts. The total estimated emissions produced as part of the decommissioning operations (2,684T) in relation to the total CO2 produced in the North Sea and ports (20,671,000T [52]) is less than 0.02%. In addition, there will be a contribution to global warming from other gaseous emissions, the overall global warming potential (GWP - a relative measure of how much heat a greenhouse gas traps in the atmosphere). The contribution will be proportional to the volume of emissions, as for CO2. Therefore the overall GPW will also constitute a relatively small increase to existing emissions. The significance of the impact of CO2 emissions from the Stamford decommissioning activities has been assessed as low.

In general, environmental conditions offshore will lead to rapid dispersion and dilution of any emissions to atmosphere. The Stamford facilities are located approximately 140km from the nearest UK coastline. Offshore weather conditions will mean that impacts will be localised and short term. It is considered that the emissions to atmosphere from the Stamford decommissioning activities are unlikely to lead to any significant impacts on either sea water quality or air quality and not have a significant contribution to global warming.

The significance of impacts on either sea water quality or air quality has been assessed as low.

Section 3.2 describes the biological environment, and therefore the receptors that could be


impacted by emissions. There are spawning and nursery grounds in the area throughout the year, likewise there will be marine mammals present throughout the year, with the highest sensitivity being during the summer months. Seabirds are present throughout the year with the winter months being the most sensitive. Vessels will be in the field during April 2015 and later in the 2015, 2016 or 2017, the dates have yet to be decided. Although there are receptors present throughout the year, given the relatively short duration of the activities and the rapid dispersion in the area the significance of the impact on the receptors is assessed as low.

5.1.3 Transboundary and cumulative impacts

The Stamford facilities are located approximately 5km east of the UK/ Netherlands median line. The transboundary impact of atmospheric emissions arising from the decommissioning activities at Stamford are expected to be of low significance owing to the rapid dispersion and dilution of emissions which will occur in offshore weather conditions and over distance.

In relation to the current levels of shipping traffic (15-16 vessels per day within 10nm) which already pass Stamford, the expected emissions from the decommissioning activities will represent a small incremental addition to emissions of combustion gases which already occur over a relatively short time period. Therefore, although the emissions to air will contribute to global warming the cumulative impact on receptors from the atmospheric emissions from the decommissioning activities for Stamford have been assessed as of low significance.

5.1.4 Control and mitigation measures

In line with the Centrica routine environmental management of vessels, a number of control and mitigation measures have been identified to optimise energy consumption and reduce the significance of the impacts from atmospheric emissions.

Prior to the mobilisation, vessels will be selected and audited to ensure maintenance of generators and engines which leads to better efficiency in line with manufacturer’s specifications;

Fuel used for mobilised vessels will comply with MARPOL [51] requirements, in particular with regard to low sulphur fuel;

Decommissioning will be planned to minimise vessel use (the vessel schedules will be optimised);

Fuel consumption will be minimised by operational practices and power management systems for engines, generators and any other combustion plant (as required under the contract with the subcontractor); and,

On board planned, preventative maintenance systems will be required for all vessels to ensure that all equipment (combustion and mechanical/electrical) is maintained at peak operating efficiency for minimum overall fuel usage (as required under the contract with the subcontractor).

5.1.5 Conclusion

The principal energy use and generation of emissions to air will arise from fuel combustion for propulsion and power generation by the vessels required for the activities. These emissions will include components which have the potential to contribute to global warming,


acid rainfall, dry deposition of particulate and photochemical pollution or cause impacts on local air quality. It is expected that impacts will be low significance as they will short term.

The energy usage from the decommissioning of the Stamford Facilities is estimated to be 36,171GJ direct (vessel use) and 12,788GJ indirect requirements (manufacture of new materials to replace those decommissioned in situ) (Table 5-3).

Emissions to atmosphere from the decommissioning activities are unlikely to significantly contribute to greenhouse gas emissions or global warming impacts; total CO2 emissions generated by the proposed decommissioning are 2,684T. In relation to the total CO2 produced in the North Sea and ports (20,671,000T [52]) is less than 0.02%.

Standard mitigation measures to optimise energy usage by vessels will include operational practices and power management systems for engines, generators and any other combustion plant and planned preventative maintenance systems for all equipment for peak operational efficiency.

5.2 Underwater noise

This section discusses the underwater noise that will be generated by the activities and the associated impact and control and mitigation measures to minimise these impacts.


Each stage of the decommissioning process has been considered in terms of underwater noise generation. Activities that will produce noise are:

Vessel use;

Jetting and cutting; and

Removal of pipeline and umbilical sections.

Noise will be created during the decommissioning operations from the vessels used, cutting methods and removal activities. The vessels that will be used include DSV, standby vessel and ROVSV.

The primary sources of sound from vessels are propellers, propulsion and other machinery ([73] and [74]). In general, vessel sound is continuous and results from narrowband tonal sounds at specific frequencies and broadband sounds. Acoustic broadband source levels typically increase with increasing vessel size, with smaller vessels (< 50m) having source root-mean-square (rms) sound pressure level (SPL) of 160-175dB re 1μPa at 1m, medium size vessels (50-100m) 165-180dB re 1μPa at 1m and large vessels (> 100m) 180-190dB re 1μPa at 1m (summarised by Richardson et al. [54]. However, sound levels depend on the operating status of the vessel and can vary considerably in time. Acoustic energy is strongest at frequencies below 1kHz.

Some of the vessels used for the proposed activities will use DP systems to maintain and adjust their position when working. Sound levels can be louder during use of DP, which requires the operation of thrusters to control a ship’s location.

Richardson et al. [54] reviewed the effects of vessel noise on marine mammals. They noted that it is not always possible to distinguish between effects due to the sound, sight or even smell of a vessel to an animal but there is evidence that noise from vessels has an impact on marine mammals. Animals have been reported to display a range of reactions from ignoring to avoiding the noise. The latter can lead to temporary displacement from an area.


Vessel noise can mask communication calls between cetaceans, reducing their communication range [75]. Exposure to low frequency ship noise may be associated with chronic stress in whales. Rolland et al. [76] reported a decrease in baseline levels of stress-related faecal hormones concurrent with a 6dB reduction in underwater noise along the shipping lane in the Bay of Fundy, Canada, in 2001.

Cutting equipment may be required to assist with the removal of the legs from the wellhead protection structure, cutting and removal of the pipeline and umbilical sections. Exact details of the cutting equipment to be used are not yet known and there is little data for these tools in terms of expected underwater noise generation.

All marine biota are receptors to noise, in particular marine mammals and fish discussed in Section 3.2.4 and Section 3.2.6, respectively.


The background noise levels present within the ocean originate from physical factors: waves, wind, the noise generated from marine mammals and shipping activities (15-16 vessels per day within 10nm).

The generation of underwater noise which leads to an increase above background noise levels will impact on marine life. Increased noise can affect behaviour and has the potential to cause injury on a number of species including fish, seals and cetaceans depending on the scale of increase.

The Stamford infrastructure is located in a well-developed oil and gas area in the North Sea with high levels of shipping activity (Section 3.3.1). Therefore, marine fauna in the area is already exposed to the types of sound that will be generated during the proposed decommissioning. The reported response of animals to received sound has been found to wane with repeated exposure in some studies [54]. Combining the relatively short exposure time with the fact that the area already has a number of vessels associated with it, it is expected that though vessels associated with the decommissioning activities will add to the background noise, the overall impact will not be significant.

Many species of fish use sound for location of prey, avoidance of predators and for social interactions. The inner ear of fish including elasmobranchs (sharks, skates and rays) is very similar to that of terrestrial vertebrates and hearing is understood to be present among virtually all fish ([55] and [56]). The sensory systems used by fish to detect sounds are very similar to those of marine (and terrestrial) mammals and hence sounds that damage or in other ways affect marine mammals could have similar consequences for fish [57]. Fish exhibit avoidance reactions to vessels and it is likely that radiated underwater noise is the cue. For example, noise from research vessels has the potential to bias fish abundance surveys by causing fish to move away ([77] and [78]). Reactions include diving, horizontal movement and changes in tilt angle [77].

The subsea noise levels generated by surface vessels used during the decommissioning phase are unlikely to result in physiological damage to marine mammals. Depending on background noise levels, sensitive marine mammals may be locally disturbed by noise from a vessel in its immediate vicinity; however, the impact is not expected to be significant. The duration of vessel use has been assumed to be approximately 31 days for the pipeline decommissioning and 5.5 days for the DSV and standby vessels required for umbilical decommissioning. The significance of the impact from the noise from these vessels is expected to be low, based on background noise from current shipping traffic in the area and the relatively short number of vessel use days required.


The pipeline and umbilical are to remain in situ, there is a need to disconnect/cut either end of the pipeline and umbilical (which may include the jetting of the ends). The impact on marine mammals from the noise associated with these activities is has been assessed to be of low significance.


As activities will take place on both sides of the Dutch / UK median line, transboundary impacts will occur. However, the significance of the impacts from all decommissioning activities has been assessed as low, therefore any transboundary impacts will also be of low significance.

Changes in sound characteristics with distance generally result in exposures becoming less physiologically damaging with increasing distance because sharp transient peaks become less prominent [47]. The underwater noise impacts from vessels, cutting of the pipeline and the removal of the umbilical are expected to be localised and short term, with no expected significant cumulative impacts.


The control and mitigation measures below will be adopted to ensure that noise levels from the Stamford decommissioning activities will be minimised where possible:

Machinery and equipment will be in good working order and well-maintained (as required under the contract with the subcontractor);

The work programmes will be planned to minimise vessel time in the field; and,

Cutting locations and procedures will be identified to minimise the number and duration of cutting in addition to reducing the probability and severity of unplanned events from these activities.

5.2.5 Conclusion

The primary source of noise from the Stamford decommissioning activities will be from the use of vessels. Given the existing background noise in the area (from natural and shipping traffic) combined with the relatively short duration of the decommissioning activities the impact from noise from the decommissioning activities will result in localised, short term impacts. Impacts from the noise is therefore expected to be of low significance.

5.3 Seabed disturbance

This section addresses the seabed disturbance resulting from the decommissioning activities. Control and mitigation measures have been identified.

The activities will cause some disturbance to the seabed. This assessment will consider the extent and duration of impacts associated with this disturbance.


The principal activities within the decommissioning project works that will disturb the seabed are:

Removal or movement of protective concrete mattresses and grout bags;


Disconnecting the flexible riser and relocation (for temporary placement and subsequent potential reuse in situ);

Disconnection of the pipeline and umbilical from the wellhead assembly, including removal of spool pieces;

Dismantling and removal of the WHPS assembly;

Lifting of spool pieces and sections of pipeline and umbilical (including jetting of the pipeline and umbilical ends to gain access for cutting);

Replacement of protective concrete mattresses and grout bags, at the flexible riser after relocation.

An estimate of the seabed area that these activities will impact is presented in Table 5-4. It shows that the estimated total area impacted in the UK is 0.0041km2 and 0.0013km2 in the NL sector. This put this into context a licence block is approximately 200km2, therefore the area impacted by the decommissioning activities is relatively small.


Table 5-4: Estimate of seabed area impacted from decommissioning activities

Infrastructure Assumptions made Area impacted (km2)

UK NL

Recovery of mattresses

To calculate the area of disturbance associated with the removal of the 32 mattresses measuring 12m x 3m an additional impacted area of 1m was assumed on each side of the pipeline

0.00192 0

Recovery of grout bags

Recovery of in the region of 100 grout bags is assumed to impact on an area of 0.5m x 0.5m.

0.000025 0

Relocation of riser

Area impacted by lifting and replacement of 20m of flexible riser

0 0.00004

Replacement of mattresses

Replacement of 3 protective concrete mattresses, at the flexible riser after relocation

0 0.00018

Removal of WHPS

Removal of 5.25m by 5.25m WHPS. An additional area of 1m around the structure was assumed.

0.00005 0

Recovery of spools

Total length of spools to be recovered is 40m. The area of seabed disturbance was assumed to be a corridor width of 10m at each of the spools as jetting will be used to clear the sediment to allow access beneath the spools to facilitate lifting.

0.00040 0

Recovery of pipeline and umbilical pipeline ends

Total length of to be recovered is 12m of pipeline in UK, 162m of umbilical in the UK and 91m of umbilical in NL. The area of seabed disturbance was assumed to be a corridor width of 10m, allowing for sediment to be moved from current location over the partially buried pipeline ends to either side. As for the spools jetting will be used clear the sediment to allow access beneath the spools to facilitate lifting.

0.00175 0.00091

Total area impacted 0.0041 0.0013

All the planned activities will lead to some degree of temporary disturbance of seabed sediment with associated increases in suspended solid concentrations in the water column and on the seabed with the potential to change the physical chemical characteristics of the seabed. The seabed characteristics are reported in 3.1.5 and 3.1.6. The seabed is mainly smooth, apart from the channel in the south west and raised feature in the north east. The 2014 survey [22] identified two main sediment types across the study area: silty fine sand with occasional shell fragments in the north east and gravelly sand with the occasional small cobbles and boulders found in the south of the survey area. The sediment chemistry is not substantially elevated above regional levels, although there is some evidence elevated concentration of drilling related determinands. Changes to the nature of the local seabed sediments may be reflected in changes in the flora and fauna, particularly as the sediments provide a habitat and food source for benthic infauna [3].

The activities with the greatest potential for disturbance are likely to be water jetting and the lifting of the pipeline and umbilical sections, which will be lifted from within the trenches or cover depending on the location. The removal will lead to disturbance of the trench itself and the immediate surrounding area.



The temporary disturbance of seabed sediment will lead to increases in suspended solids concentrations in the surrounding waters. However, suspended materials will be rapidly dispersed and diluted by prevailing hydrodynamic conditions before settling back to the seabed and the disturbance will therefore be short term. Whilst some redistribution of material is to be expected, seabed composition in the area small that will be impacted is largely uniform. Long term impacts are therefore not anticipated and the risk of habitat modification (due to the relatively homogenous nature of the sediment) is considered to be low. Since the 2007 and 2014 survey results (Section 3.1.6) show that there is little contamination of the sediment in the area and there has been improvement between 2007 and 2014, any contamination release with the suspended solids is not anticipated to have a significant impact.

Localised disturbance of the ecosystem at the seabed may occur, leading to some degree of community change. It is known that some bottom-dwelling marine organisms are particularly vulnerable to natural or man-made activities which cause disturbances of the seabed, such as deposition of sedimentary material. The majority of offshore species are recruited from the plankton, benthic populations which usually recover rapidly once disturbance from the decommissioning activities cease. Results of the sediment particle size analyses revealed that sediments are varied overall but locally homogenous, therefore seabed disturbance is likely to be spatially limited rather than across the area as a whole [20].

There may be the potential for sub-lethal impacts on benthic and epibenthic fauna as a consequence of physical abrasion, but because of the relatively small area being impacted (a 10m corridor along the spool pieces and pipeline and umbilical ends of the pipeline) this is low. Careful management and planning of activities to minimise affected areas will reduce the potential for physical abrasion but it is impossible to eliminate the risk entirely and some impacts on populations may occur. Since the disturbance will be short term and given the local currents in the area (evidence being that cuttings released during drilling are not evident at the well as a result of the local currents), it is expected that any impacts on the populations and the wider ecosystem will be minimal and that rapid and complete recovery of the localised seabed community will occur once activities cease.

It also possible that bottom-dwelling organisms may be smothered by settlement of suspended solids, however rapid dispersion and dilution by prevailing hydrodynamic conditions before the material settles back to the seabed will prevent the development of substantial accumulations of re-settling materials far from the trench. The risk of smothering is therefore considered to be in line with the normal re-distribution of seabed sediment which occurs as a result of natural hydrodynamic conditions and is an inherent component of the ecosystem.

The ecosystem and any specific populations are expected to recover rapidly once decommissioning activities cease as supported by the results from the Gardline survey 2007 and 2014 showing that the area is broadly in line with that expected for the area and that recovery had taken place between 2007 and 2014. The large proportion of low abundance taxa recorded suggests that the community found in the survey area has been subject to relatively little pollution or disturbance stress [20] and therefore that the impacts from pipelay activities are not evident.

Following the assessment above it is not expected that significant long term impacts will occur to the seabed environment (distance, habitat modification). Impacts on the seabed and its associated ecosystem are likely to be short term and the rapid recovery of ecosystems


and specific population is anticipated once activities have been completed.

The extended presence of the pipeline and umbilical post-decommissioning is not expected to lead to any identifiable impacts since, for the main part, the depth of burial is to remain greater than 0.6m along the length or under rock dump.


Due to the homogeneous nature of the seabed, the impacts from the activities are expected to be localised with only short term effects on the seabed, therefore, significant cumulative impacts are not anticipated.

Transboundary impacts will occur due to the pipeline and umbilical spanning both the UK and Netherlands waters, the impacts will be of low significance to the seabed on both sides of the median line.


All activities which may lead to seabed disturbance will be planned, managed and implemented in such a way that the potential for disturbance is minimised.

Particular attention will be paid to those activities with the greatest potential to cause disturbance, i.e. the selection of appropriate water jetting and the lifting activities.

5.3.5 Conclusion

Whilst some disturbance of the seabed will inevitably occur it is expected that effects on the seabed sediment and the benthic ecosystem will be short term and that recovery will occur once activities have been completed. Therefore the significance of impacts on the seabed from disruption is expected to be is low.

5.4 Discharges and releases to sea

This section discusses the potential for discharges (planned) and releases (unplanned) to sea which may arise as a consequence of the decommissioning operations, with the exception of large hydrocarbon releases which warrant a separate section (Section 5.5). The proposed control/mitigation measures to be implemented in order to minimise impact of discharges to sea and the likelihood of releases are also discussed.


The decommissioning operations have the potential to lead to the discharge and release of liquids and/or solids into the sea. Whether these discharges actually occur is influenced by the following factors:

The effectiveness of the preparation and pre-decommissioning activities;

Operational practices and procedures adopted by vessels (both at the surface and subsea), including accident prevention measures; and,

Maintenance practices and procedures of the vessels intended to secure the containment integrity of all equipment (e.g. pipework).

The following sources of potential discharges and releases to sea during the decommissioning process have been identified:


Planned discharges of treated water arising from decommissioning activities from the Markham Platform or vessels in the field;

Planned discharge of AQUALINK 300F VER2 (the hydraulic fluid), the Aqua-Glycol 24F (in the unused chemical cores from installation) or residues of other chemicals remaining after the cleaning and flushing operations (methanol and corrosion inhibitor) from the umbilical when containment is broken;

Planned discharge of residual chemicals from the pipeline when containment is broken including naturally occurring radioactive material (NORM);

Marine growth from the exterior of removed wellhead, pipeline and umbilical sections and mattresses and grout bags which will be removed;

Planned, routine discharges and / or unplanned releases and discharges from vessels operating in the field.

The above discharges and releases into the water column or at the seabed from decommissioning activities will impact plankton, benthos and fish in the immediate vicinity of the discharge point. Bioaccumulation in the food chain may occur depending on constituents characteristics [57].

During production, chemicals were injected on a continual basis at the wellhead. These chemicals were methanol and a corrosion inhibiter and were selected to prevent the formation of corrosion and hydrate. Any discharged to sea would be slowly overtime as the umbilical degrades under the seabed and would be extremely small of the remaining following umbilical flushing and cleaning.

A hydraulic fluid (AQUALINK 300F VER2) was used to actuate the valves and will remain in the umbilical. When the umbilical was installed the methanol cores were filled with Aqua-Glycol 24F. The use and discharge of both were permitted at the time of installation. Two of the four cores have not been used and therefore still contain Aqua-Glycol 24F. The total volumes of AQUALINK 300F VER2 and Aqua-Glycol 24F are 10m3 and 4m3 respectively (Table 2-1). The content of the cores will be slowly discharged to sea as the umbilical degrades under the seabed.

Both AQUALINK 300F VER2 and Aqua-Glycol 24F are a commonly used hydraulic fluid for subsea systems. Each time subsea valves are actuated a small operational discharge of hydraulic fluid occurs at the valve location. The discharge is assumed to be 100% of the content of the system. They are both OCNS D registered, which is the second lowest hazard category, corresponding to an aquatic – toxicity of between >100-1,000 ppm.

For AQUALINK 300F VER2 an Osbourne Adams risk assessment has been performed for discharge subsea, based on a daily discharged volume of 0.1 tonnes (0.094m3) in a 24 hour period. This was used for operational purposes, but is used here to represent the release over time from the umbilical once decommissioned. The assessment found that the discharge is not expected to be hazardous to the receiving environment. A full assessment will be completed and submitted with the chemical permit for the decommissioning operations, as appropriate

Given that the discharge has already been risk assessed and permitted showing that there would be very limited environmental impact the AQUALINK 300F VER2 and Aqua-Glycol 24F will be left in the umbilical, rather than recover it for onshore disposal which would incur additional environmental impacts in relation to transport and treatment and increase the potential for unplanned releases.


The environmental impact of the fluids eventual discharge when the pipeline and umbilical are cut will be assessed and permitted via MATs/SATs prior to the activities being undertaken, as appropriate.


Treated water and chemicals

Following the preparatory and pre-decommissioning activities the pipelines and umbilical will be left flooded with inhibited seawater and potable water, respectively (notwithstanding the AQUALINK 300F VER2 and Aqua-Glycol 24F, covered under hydraulic fluids below). (There will only be residual chemicals after cleaning.) As a result, the impact from discharges from the pipeline and the umbilical during the decommissioning activities have been assessed to be of low significance.

The level of residual hydrocarbon contamination remaining within the pipeline following pigging and cleaning is expected to be at a level where the environmental impact would be of low significance if discharged. The likelihood of detectable impacts on the surrounding waters from discharges of small quantities of residual hydrocarbon is considered to be negligible as hydrodynamic conditions at the seabed are likely to be such that rapid dispersion and dilution will occur. Any impacts will be localised, short term and small. The discharge of any residual hydrocarbon or chemical to sea is therefore not expected to lead to any impact on the surrounding waters. Any hydrocarbon discharges will be permitted under the Offshore Petroleum Activities (Oil Prevention and Control) Regulations 2005 (as amended) (OPPC) prior to undertaking the activities.

No accidental releases are foreseen from the pipeline or umbilical as the residual content will be permitted, and therefore all discharges will be planned.

Where discharge of chemicals during the decommissioning activities is proposed, these discharges will be subject to a chemical risk assessment and permitting under the Offshore Chemicals Regulations 2002 (OCR).

Hydraulic fluid

As stated above, both AQUALINK 300F VER2 and Aqua-Glycol 24F are commonly used hydraulic fluids for subsea systems. Hydraulic fluids are specifically selected, water-soluble chemical with low environmental toxicity and are permitted for use and discharge under the Offshore Chemicals Regulations 2002 [9]. The impact of the discharged hydraulic fluid is expected to be minimal since the selected fluid is in Hazard Quotient category D and a risk assessment for their discharge during operations has been undertaken which concluded that it is not expected to be hazardous to the receiving environment. A full assessment will be completed and submitted with the chemical permit for the decommissioning operations.

Naturally Occurring Radioactive Material

Levels of NORM in the produced gas and condensate from Stamford were historically low and there is therefore little likelihood that any remaining residual contamination in the gas pipeline will contain detectable levels of radioactive material. As a consequence, the impacts on the surrounding waters and the associated ecosystem arising from NORM discharge has been assessed as of low significance.

Marine growth

It is possible that the exposed pipe spools, separated unburied pipeline and umbilical sections and wellhead may have accumulated marine growth which would need to be


removed prior to handling/ lifting activities in order to secure safe operation and controlled occupational exposure for operational staff. Since such growth is entirely organic in origin, cleaning this off in the marine environment is unlikely to lead to impacts other than a short term increase in suspended solids which is likely to be rapidly dispersed by hydrodynamic conditions. Removed marine growth will naturally biodegrade within the normal ecosystem cycle and it is highly unlikely that it will lead to detectable impacts.

Discharges and releases from operating vessels

Discharges to sea from the vessels in the field are characterised as normal, operational discharges which are subject to on-board control measures and designed to secure compliance with the requirements of MARPOL 73/78 [51]. Discharges to sea include:

Ballast water;

Bilge water;

General shipboard drainage;

Treated sewage and grey water from accommodation and amenities; and,

Unplanned releases of diesel, hydraulic fluid or other hydrocarbons.

Whilst the vessels will be in the field for a period of up to approximately 31 days rather than transiting through the area, discharges will be controlled and minimised. For example by operating procedures and systems for optimum performance, including planned preventative maintenance systems for peak operating efficiency of on-board systems for the management of effluent, ballast water and bilge water. The water quality immediately around the site will be reduced at the time of discharge, as with routine vessel discharges, the impacts will be minimised due to the rapid dilution and dispersal of any pollutants. Since discharges to sea from the vessels in the field may be characterised as normal, operational releases within the constraints of MARPOL 73/78 [51], it is unlikely that impacts beyond those associated with normal shipping activities will occur. Impacts are therefore anticipated to be short term and localised.


Transboundary impacts arising from discharges and releases to sea as a consequence of the decommissioning activities are expected to be low in both UK and Netherlands waters. The impacts will be transient and highly localised with the significance of long distance impacts being low.

Discharges and releases to the marine environment may lead to short-term, localised impacts on marine organisms which are relatively close to the discharge point. Cumulative impacts are considered to be highly unlikely since the impacts arising from discharges are expected to be short term with rapid dispersion and degradation.


All operational activities will be undertaken in compliance with regulations (particularly OPPC and OCR and MARPOL 73/78 [51] and all its annexes).

Control and mitigation measures for discharges and releases to sea will include:

Procedures and systems for the minimisation of waste and effluent generation maintained (as required under the contract with the subcontractor);


Procedures and systems for the management of ballast and bilge water maintained (as required under the contract with the subcontractor);

Accident prevention measures will be in place in order to minimise the potential for accidental spillages of hydrocarbons or other polluting materials;

Vessels will be selected and audited to ensure that effective operational systems and on-board control measures are in place; and,

Decommissioning plans will be designed to achieve optimum utilisation of vessels within the field to minimise time in the field.

5.4.5 Conclusion

Discharges to sea will comprise either residual chemicals / hydrocarbons following pipeline and umbilical cleaning, relatively small volumes of AQUALINK 300F VER2 and Aqua-Glycol 24F, marine growth and discharges from vessels. Given the nature of these discharges and that they will be rapidly dispersed and diluted by prevailing hydrodynamic conditions the significance of the impacts have been assessed as low.

5.5 Large hydrocarbon releases and oil spill response

Offshore oil and gas sector activities generally have the potential for release of hydrocarbons, which may have detrimental impacts on the sea and associated marine ecosystems. This section considers the potential for large hydrocarbon releases (synonymous with as unplanned discharges or accidental events) and the prevention measures to be adopted to reduce the probability of accidental events.

In the event of a large hydrocarbon release (most likely from diesel inventory from vessels), the DECC approved Greater Markham Area OPEP produced by Centrica or the vessels Shipboard Marine Pollution Emergency Plan (SOPEP) will be deployed (67).


Releases to sea

Centrica has undertaken a hazard identification and spill probability assessment focusing on the subsea infrastructure and associated decommissioning activities in the Stamford area. This assessment identified the following scenarios as potential sources of hydrocarbon releases:

Loss of fluids from subsea wellheads (considered to be highly unlikely as the well no longer flows and the pressure will have been brought down to ambient prior to the start of decommissioning), therefore it is not considered further;

Release of diesel from a vessel (due to collision or other event).

Accidental diesel release

By far the worst case scenario in terms of potential impact from a release is an immediate catastrophic scale spillage of diesel from the support vessels as a consequence of vessel collision, vessel sinking, or failure of the diesel storage tanks leading to immediate release of diesel to the sea. These release scenarios are considered to be highly unlikely owing to the control measures and operational procedural systems which are in place for the management of vessel operations whilst in the Stamford Field. It is nonetheless conceivable


that a release could occur with sufficient quantity of material released to, without additional assessment, be perceived to present a risk of significant impacts and more detailed assessment is therefore considered to be appropriate.

In order to determine the potential significance of a diesel release the scenario from the OPEP OSCAR modelling, which is comparable to the accidental release of diesel from a support vessel is the instantaneous release of 3,550m3 of diesel from the Markham Platform. This is inherently conservative in terms of impact assessment, since the expected maximum diesel release from a single vessel is less than 1400m3 and accident scenarios involving multiple vessels are considered to be highly improbable. Nevertheless, the size of the modelled release from the platform is such that an accident scenario involving multiple vessels and a larger aggregate diesel release is covered, even though such a scenario is not considered to be a realistic prospect.

Stochastic modelling outputs (see Appendix C) for instantaneous release of 3,500m3

of diesel were as follows

Surface Oiling Probability

The results indicate that the prevailing weather and metocean conditions would transport the diesel primarily in a north-easterly to easterly direction towards the Netherlands sector. The results show the spill covering an area around the well, extending over the southern part of the closest protected area, the Markham Triangle, north of the well.

Shoreline Oiling

The model predicts a maximum 0.96% probability of shoreline contamination affecting the East Anglian coast of the UK (around Cromer and Lowestoft) and the east coast of the Netherlands (around Den Helder, De Koog, Duinen van Texel and West-Terschelling); the shortest predicted beaching time is 8 days, with a maximum cumulative volume of 3.88m3 coming ashore.

The deterministic modelling outputs (see Appendix C) indicated the following outcomes for the 2 scenarios modelled.

Instantaneous diesel release of 3,550m3 from the Markham Platform location towards offshore Netherlands

After 21 days, a constant 30 knot offshore wind (direction: 256°) is predicted to result in a patchy surface slick spreading in an easterly direction. The maximum area of surface coverage was 13 km2 after 18 hours, with a corresponding surface diesel volume of 56.2 m3. Visible patches of surface diesel are predicted to cross the Netherlands median line 3 hours after the initial release.

Three days and 18 hours after the release stopped, the total volume of diesel on the sea surface decreased to below 1m3, at which point the spill may be considered fully dispersed (this small quantity is predicted to be spread between a large number of discrete thin patches).

Six days and 21 hours after cessation of the release, the volume of diesel on the sea surface is predicted to decrease to below 0.1m3.

Shoreline contamination is not predicted to occur at any location.

Instantaneous diesel release of 3,550m3 from the Markham Platform location towards onshore UK

After 21 days, a constant 30 knot onshore wind (direction: 045°) is predicted to result in a


patchy surface slick spreading in a south-westerly direction. The maximum area of surface coverage was 9.03 km2 after 18 hours, with a corresponding surface diesel volume of 40.7 m3. Visible patches of surface diesel are predicted to cross the Netherlands median line 1 day and 18 hours after the initial release.

Two days and 12 hours after the release stopped, the total volume of diesel on the sea surface decreased to below 1 m3, at which point the spill can be considered fully dispersed (this small quantity is predicted to be spread between a large number of discrete thin patches).

Four days and 12 hours after cessation of the release, the volume of diesel on the sea surface decreased to below 0.1 m3.

Shoreline contamination is not predicted to occur at any location.

The full modelling output for the release of diesel is included in Appendix C.


As a consequence of the control measures in place for operational activities relating to the handling of diesel, the likelihood of a major hydrocarbon release is considered to be very low. The low likelihood is supported by historical spill reporting data, two examples of which are:

PON1 data from 2011 – 2014 showed that there were only four hydrocarbon releases over 1 tonne with the largest being 7.16 tonnes (although it is acknowledged that larger spills may have occurred which are not reportable under PON1s).

The summary of spills from the most recent vessel data published by ACOPS for 2012 reported 37 incidents of which the largest was 605.5 tonnes (from an unknown source) [72]. The report states that each incident was believed to have dispersed naturally without posing a threat to wildlife or the coastline.

A large diesel release is very unlikely, however should it occur it would present a risk to the marine environment.

Appendix C shows the modelled fate of a worst case diesel spill. The modelling shows a catastrophic, worst case event of the instantaneous loss of the complete diesel inventory of several vessels. In addition the modelling is undertaken using environmental conditions that would be lead to the worst case impact. It predicts that after 10 days 820.05m3 will have evaporated and 1,288.65m3 will have decayed. It also predicts that 145.195m3 will be submerged and 1,295.75m3 will be in the sediment. It should be noted that the default sediment type silt was used in the modelling, whereas the sediment type in the area is predominantly sand. Therefore the results of the modelling will be conservative, showing a higher volume of diesel remaining in the sediment.

Surface and near-surface dwelling ecosystems and species would be at risk of harm as a consequence of such a release. Fish, sea birds and marine mammals are the most likely groups to be impacted. The severity of the impact would depend on the variety and numbers of vulnerable species present at the time of the release and during the presence of the hydrocarbon on the sea water surface. Section 3 identified that seabirds are most vulnerable during November and December, fish throughout the year and marine mammals during June, August and September. The modelling showed that after 10 days only 0.355m3 would remain on the surface, therefore this risk is relatively short term. Given the low likelihood of the release of a large volume of diesel and the short duration the diesel is predicted to


remain on the surface combined with the mitigation and control measures in place the significance of the impact on surface and near-surface dwelling ecosystems and species has been assessed as low.

The receptors to the diesel partitioning to the sediment would include the benthic community (including sand eels), Cleaverbank SAC, the Markham Triangle MCZ which is proposed for designation primarily for the seabed which supports a diverse benthic community and organisms that feed on sand eels higher up the food chain including marine mammals.

Benthic species are exposed to sediment hydrocarbons in and around the sediment/water interface for longer and thus may accumulate higher levels of toxic hydrocarbons than species in the water column [71]. In response to oil exposure, benthic invertebrates can either move, tolerate the pollutant or die, depending on the life cycle, feeding behaviour as well as ability to metabolise toxins, especially PAH compounds. The impact on benthic communities from elevated levels of hydrocarbon is not well defined. Recolonization rates are affected by the type or organism, time of year, availability of juvenile recruits, climatic conditions and many other influences. There is a lack of long-term studies that could reveal indirect or protracted impacts ([81] & [85]). Some reviews indicate that recovery from oil spills occurs within three years ([83] & [84]) where as others find that recovery requires up to ten years ([82], [80] and [85]). In general more dynamic environments recover more quickly than sheltered environments.

The amount of diesel that will remain in the sediment is dependent on the sediment type, with more partitioning to the silt fraction than sand. The sediments in the Stamford area are presented in Section 3.1.5 and are muddy sand and slightly gravelly muddy sand. The modelling used the default setting of silt.

Under the modelled worst case conditions, the area over which the 1,295.75m3 partitions to the sediment is in the region of 2,403km2 as shown in Appendix C at 10 days. The modelling showed the volume in the sediment to be greatest after 4 days and decreasing from then on. At 10 days majority area has a relatively low concentration of less than 0.1kg/m2 this includes an area in the south of the Cleaverbank SAC and the Markham Triangle MCZ.

It is, therefore, possible that the benthic communities within the Cleaverbank SAC and the Markham Triangle MCZ could be impacted by a worst case diesel release, however, the concentration of the diesel in the sediment is relatively low, the modelling is worst case (large instantaneous release of total inventory) and conservative due to silt being assumed rather than sand and the likelihood of a release is very low. Recovery rates are unknown, however as the area is not sheltered, the recovery rate is anticipated to be relatively quick. With these considerations combined with the control and mitigation measures in place, the overall significance of the impact on benthic communities and the effect on organisms higher up the food chain is low.


The principal risk of hydrocarbon release from the Stamford activities is from diesel fuel, which has a limited potential for impact on the environment. In conjunction with the procedural response and mitigation/control measures to any diesel release, it is unlikely that releases would remain present in the environment for extended periods as they will evaporate and be dispersed by weather and currents. There is, therefore, limited potential for cumulative or transboundary impacts.



Centrica has well developed procedural controls in place to minimise the likelihood of releases and the Greater Markham Area OPEP to mitigate the impacts of releases should they occur. All vessels undertaking decommissioning activities will have an approved Shipboard Oil Pollution Emergency Plan developed within the requirements of Regulation 37 of MARPOL Annex 1 [51].

These control measures are considered to be effective in reducing and minimising the risk of release during the decommissioning activities to as low as reasonably practicable.

5.5.5 Conclusion

Whilst there is the potential for a major diesel release during the decommissioning activities the likelihood is low. The potential consequence is severe however with additional assessment given the types of sediment and receptors in the area and when the mitigations and controls are applied, the overall significance of the impact has been assessed as low.

5.6 Waste

5.6.1 Regulatory requirements

The Revised Waste Framework Directive (WFD) (Directive 2008/98/EC) was adopted in December 2008 [59], with Member States being required to implement revisions by December 2010. The overriding aim is to ensure that waste management is carried out without endangering human health and without harming the environment. Article 4 also states that the waste hierarchy shall be applied as a priority order in waste prevention and management legislation and policy.

The Waste (England and Wales) (Amendment) Regulations 2012 [60] outlines the requirement for collection, transport, recovery and disposal of waste. It sets out the principles of the waste hierarchy which should be considered when treating and handling waste. In addition, the DECC Guidance Notes [2] under the Petroleum Act 1998 [1] have a requirement for all decommissioning decisions to be made in line with the waste hierarchy.

Whether a material or substance is determined as a ‘waste’ is determined under EU law. The EU WFD (2006/12/EC) [59] defines waste as:

“any substance or object in the categories set out in Annex 1 of the Directive which the holder discards or intends or is required to discard”.

Materials disposed of onshore must comply with the relevant health and safety, pollution prevention, waste requirements and relevant sections of the Environmental Protection Act 1990 [13]. The waste management assessment is based on the worst case scenario but for production was waste in line with relevant legislation, permits and consents (Figure 5-1).

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material recovered to shore are presented in Table 5-5 and Table 5-6. For consistency these tables are as stated in the Decommissioning Programme [58] and include mattresses and grout bags.

Table 5-5: Inventory disposition

Inventory (excludes

rock)

Region Total

Inventory Tonnage

Planned tonnage to shore

Planned tonnage to be

decommissioned in situ

Planned tonnage left in-situ for potential re-

use or deferred decommissioning

Installations UK 54 54 0 0

Netherlands 0 0 0 0

Pipelines UK 674 222 451 451

Netherlands 424 3 194 227

Table 5-6: Re-use, recycle & disposal aspirations for material recovered to shore

Inventory Region Re-use Recycle Disposal

Installations UK Approx. 40% Approx. 60% <5%

Netherlands n/a n/a n/a

Pipelines UK <5% Approx. 95% <5%

Netherlands <5% Approx. 95% <5%

The planned tonnage to shore includes, pipe spool pieces, sections of pipeline, umbilical, mattresses, grout bags, the WHPS, the tree and the wellhead itself. Figure 5-2 shows a pie chart of the material breakdown for the material recovered to shore associated with the pipeline and umbilical (including mattresses and grout bags). No pie chart is shown for installations as all material is steel.

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The activities identified have been assessed in terms of the sources themselves and how the decommissioning operations have or may impact the activity during and post decommissioning.

The sources of impact on socioeconomic activities:

The use of vessels for the decommissioning activities

Handling and treatment of waste onshore

The presence of the Stamford pipeline and umbilical following decommissioning

The requirement for legacy surveys

A number of socioeconomic receptors, which could be impacted as a result of the decommissioning operations are listed below:

Industry - oil, gas and fishing activities;

Employment;

Shipping;

Wind farms; and,

Communities local to onshore sites.

The impacts on commercial activities (fishing, oil and gas, shipping) has been assessed against the current levels in the area; there is vessel use in the Stamford area to conduct inspections, repair and maintenance. The shipping traffic around this area within 10 nautical miles contributes to 15-16 vessel movements per day [3].

The most beneficial socioeconomic impact will be the short-term continuation of jobs on vessels. Stamford activities will help maintain the local economy and will maintain employment levels. The benefits of employment as part of the decommissioning operations are in terms of vessel use duration and waste management requirements.

Stamford is located within the Hornsea wind farm licensed area, although there is currently no development in this area.


The impacts from the decommissioning operations, which may affect the socioeconomic activities in the area are detailed, below.

The pipeline and umbilical being left in situ will be a long term presence which may have a potential for interference for fishing equipment (albeit low as they are buried), nevertheless compared to infrastructure on the seabed prior to decommissioning, there will be a reduction overall. Following the decommissioning activities the area will be over trawled, to verify that it doesn’t present an obstruction to other sea users.

During the decommissioning operations there will be a period of time, when the well area and pipeline ends will not be available for fishing, however these are within a 500m exclusion zone, therefore fishing is currently excluded. Fishing users of this area will be pre notified of the decommissioning activities and the length of time. This is expected to have a low impact as the duration of the activities is relatively short and within existing 500m exclusion zones (well end and at the Markham Platform). The impact on fishing following the


decommissioning is expected to positive as the 500m exclusion zone around the well will be removed, allowing access for fishing.

The decommissioning impacts on employment will have a positive impact, due to vessel use, legacy surveys and waste management, although the impact will be negligible due to a communities being already altered due to the oil industry.

There will be a short period of time during the decommissioning activities when the presence of vessels around the Stamford facilities (the well end and at the Markham Platform) will be higher than the normal shipping activity. With the exception of transits, the activities will be undertaken with the existing 500m exclusion zones, where general shipping movements are excluded. The increase in number of vessels in the area (estimated at 3 at one time) is relatively low when compared to existing shipping levels in the area (15-16 vessels per day within 10nm). Overall, given the 500m exclusion zones and the existing shipping in the area the impact on shipping will be low.

Decommissioning is unlikely to have any impact on the potential wind farm development. During the decommissioning operations there will be the presence of additional vessels in the area. The development of the wind farm is expected to be commissioned in a different area initially (to the west). Post decommissioning, the presence of the buried pipeline and umbilical may present a small restriction to the locating of wind turbines, but when compared to the size of the area licences for the windfarm the impact is low. Therefore it is not expected that the Stamford decommissioning will affect the development of the windfarm.


The cumulative impacts on socioeconomic activities are expected to be limited and localised, predominantly affecting fishing and shipping. Should other pipelines in the area (Figure 3-9) be decommissioned by leaving them in situ (or partially in situ), there will be a cumulative legacy impact (Table 5-7), however, given the relatively small number of pipelines in the area the overall area affected by all the pipelines (0.003km2) will be relatively small.

Table 5-7: Cumulative Legacy Seabed Take

Pipeline description: To – From Pipeline length (km) Area (km2)

Stamford to Markham Platform 7 0.007

Grove to Markham Platform 16.5 0.0165

ST-1 to Markham Platform 6 0.006

Chiswick to Markham Platform 18 0.018

J3C to Markham Platform 1 0.001

K1-A to Markham Platform 9.1 0.0091

K4-aD to Markham Platform 7.3 0.0073

Total area impacted 0.0030

Given the location of Stamford crossing the UK and NL median line, transboundary impacts are anticipated as part of the decommissioning operations, however the level of impact is low and this is reflected on both sides of the median line.



The decommissioning activities and timing will be discussed with users of the sea in the vicinity of Stamford, this will reduce the impact to commercial users of the area, with respect to the presence of vessels at the site.

An over trawl will be conducted and any remaining debris will be removed post decommissioning.

Long term mitigation specifically for the pipeline and umbilical being left in situ require that monitoring is conducted following decommissioning to ensure that they remain buried and do not become damaged or a hazard over time. This monitoring will be carried out at appropriate intervals following decommissioning and will also be used to identify potential snagging issues in the long term.

5.7.5 Conclusion

Impacts on commercial activities, such as oil and gas operations and shipping will be low.

Access to the area for fishing will be restricted whilst decommissioning is undertaken and this will lead to short term impacts on the fishing industry although the impact will be low owing to the short duration, presence of 500m exclusion zones and relatively small nature of the activities.

A beneficial socio-economic impact is the short-term continuation of jobs in onshore yards and on vessels. It is expected that the overall impact will be low since the local socio-economic system is already altered owing to the presence of the oil industry itself.

Stamford is located within an area licensed for wind farm development but it is unlikely that there will be any impact on such development given that it is expected to be commissioned in a different area initially (to the west). Post decommissioning, the presence of the buried pipeline and umbilical may present a small restriction to the potential area for locating wind turbines but in the context of the size of the area licenced for a windfarm, the impact is expected to be minor.

Although the pipeline and umbilical will be left in situ, a post decommissioning over trawlable survey will verify that no obstructions likely to snag fishing trawls remain. In the longer term, the decommissioning of Stamford may have a positive impact on the fishing industry as the 500m exclusion zone at the Stamford wellhead will be removed.

Overall, significance of the socio-economic impacts as a result of the decommissioning is expected to be low, with the exception of the fishing sector, where there is potential for a positive impact.


6 CONCLUSIONS

Stamford is to be decommissioned by Centrica in 2015-2017. A Comparative Assessment has been carried out in order to identify the recommended decommissioning option. The EIA assessed the environmental risks and impacts associated with this selected option; the partial removal of the pipeline and the control umbilical. Included in the decommissioning activities is the removal of the WHPS, pipeline spool pieces, ends of the pipeline and umbilical that is insufficiently buried, removal of the mattresses and grout bags at the well end of the pipeline. At the platform end the flexible riser will remain, for a potential reuse opportunity along with the mattresses and grout bags associated with the riser. Also a short section of umbilical will be left under these mattresses for removal at the same time as the Markham Platform.

The impacts of all activities were assessed at a workshop, with the following areas being considered in more detail: energy use and atmospheric emissions, underwater noise, seabed disturbance, socioeconomic impacts, discharges to sea, accidental releases and waste.

A summary of the key environmental sensitivities are presented in Section 3, Table 3.8 and the outcome of the EIA is presented in Section 5. The key points from the EIA are summarised below.

Energy use and atmospheric emissions

The principal energy use and generation of emissions to air arise from fuel combustion for propulsion and power generation by the vessels required for the activities. These emissions will include components which have the potential to contribute to global warming, acid rainfall, dry deposition of particulate and photochemical pollution or cause impacts on local air quality. It is expected that impacts will be of low significance as they will be short term and a minimal increase above background concentrations.

The energy usage from the decommissioning of the Stamford Facilities is estimated to be 36,171GJ direct (vessel use) and 12,788GJ indirect requirements (waste management and the energy equivalent of lost material - manufacture of new materials to replace those decommissioned in situ).

Emissions to atmosphere from the decommissioning activities are unlikely to make a significant contribution to greenhouse gas emissions or global warming impacts; total CO2

emissions generated by the proposed decommissioning are 2,684T. In relation to the total CO2 produced in the North Sea and North Sea ports (annually 20,671,000T [52]) represents less than 0.02%.

Standard mitigation measures to optimise energy usage by vessels will include selection of vessels and the management of the vessel contractor, operational practices and power management systems for engines, generators and any other combustion plant and planned preventative maintenance systems for all equipment for peak operational efficiency.

Underwater noise

The primary source of noise from the Stamford decommissioning activities will be from the use of vessels. Given the existing background noise in the area (natural and shipping traffic), albeit not using dynamic positioning, combined with the relatively short duration of the decommissioning activities the impact from noise from the decommissioning activities will result in localised, short term impacts. The impact from the noise therefore is expected to be of low significance.


Seabed disturbance

Whilst some disturbance of the seabed will inevitably occur it is expected that effects on the seabed sediment and the benthic ecosystem will be short term, localised and that recovery will occur once activities have been completed. Therefore the significance of impacts is low.

Discharges to sea

Discharges to sea will comprise either residual chemicals / hydrocarbons following pipeline and umbilical cleaning, AQUALINK 300F VER2 and Aqua-Glycol 24F, marine growth and discharges from vessels. Given the nature and relatively small quantity of these discharges and that they will be rapidly dispersed and diluted by prevailing hydrodynamic conditions the significance of the impacts have been assessed as low. These conclusions will be confirmed and supported by the risk assessments that will be prepared and included in the permits required under the OCR and OPPC for the discharges.

Oil Spill Response

Whilst there is the potential for a diesel release during the decommissioning activities, likelihood of an event occurring is low. The consequence for surface or near surface organisms has been assessed as low due to the relatively rapid evaporation and degradation of surface diesel spills. The consequence on benthic organisms has been assessed as low given the wide area the diesel would be partitioned combined with historic evidence showing that the presence may not significantly affect the communities and the recovery should be relatively quick. The likelihood of occurrence and severity of the impacts are controlled and mitigated though procedures and oil pollution emergency response planning in the GMA OPEP and the vessel SOPEPs.

Waste

Waste will be returned to the country of origin, where it will be handled and disposed of in accordance with the legislation. Segregating materials at source and maintaining this separation between hazardous and non-hazardous streams will reduce the amount of material requiring treatment onshore.

Socioeconomic impacts

Impacts on commercial activities, such as fishing activities, oil and gas operations and shipping will be low due to the relatively short duration of the activities.

Access to the area for fishing will be restricted whilst decommissioning is undertaken and this will lead to a short term and very localised impact on the fishing industry (predominantly demersal fisheries) although the impact will be low owing to the short duration and relatively small scale of the activities.

The most beneficial socio-economic impact will be the short-term continuation of jobs in onshore yards and on vessels. It is expected that the overall impact will be low since the local socio-economic system is already altered owing to the presence of the oil industry itself.

Stamford is located within an area licensed for wind farm development but it is unlikely that there will be any impact on any future development. Post decommissioning, the presence of the buried pipeline and umbilical may present a small restriction for locating wind turbines, but this is small when compared to the size of the area licenced for the windfarm. Overall the impact is expected to be low.

Although the pipeline and umbilical will be left in situ, a post decommissioning sweep will


verify that no obstructions likely to snag fishing trawls remain. In the longer term, the decommissioning of Stamford may have a positive impact on the fishing industry as the 500m exclusions around the wellhead will be removed.

Overall, significance of the socio-economic impacts as a result of the decommissioning is expected to be low, with the exception of the fishing sector, where there is potential for a small positive impact from the return of the 500m exclusion zone for fishing.

Transboundary and cumulative impacts

Given the location of Stamford, there will be impacts in both the Dutch and UK sectors. All impacts including transboundary following the application of suitable mitigation measures, have been assessed as of low significance.

The cumulative impact of the Stamford decommissioning activities has been assessed as low based on the relatively short duration of the activities, the associated low significance of the impacts combined with Stamford being located in an area developed for oil and gas activities with existing shipping activity in the area.

Overall

The initial environmental workshop and the subsequent environmental impact assessment has concluded that all impacts and risks identified were within the low category and reduced to ALARP. Overall, the potential for significant impacts as a consequence of decommissioning Stamford is low and that most effects will be short term, localised and with low potential for long term wider field impacts.


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[58] Centrica Energy. (2014) Stamford Decommissioning Programme, CEU-PRJ-GMA-0042-REP-0009. November 2014.


[59] Waste Framework Directive. (2006). Directive 2006/12/EC of the European Parliament and of the Council of 5 April 2006 on waste. Official Journal of the European Union, 144 (9).

[60] The Waste (England and Wales) (Amendment) Regulations. (2012). Environmental Protection, England and Wales. SI No. 2012/1889.

[61] Radioactive Substances Act. (1993). Crown Copyright 1993. Reprinted in the UK by The Stationery Office Limited. Dd.141345. 8/99.

[62] Spent Fuel and Radioactive Waste Directive. (2011). Council Directive 2011/70/Euratom of 19 July 2011 establishing a Community framework for the responsible and safe management of spent fuel and radioactive waste. Official Journal of the European Union, 199 (48).

[63] The Carriage of Dangerous Goods and Use of Transportable Pressure Equipment Regulations. (2009). Health and Safety. SI NI. 2009/1348.

[64] Shipment of Waste Regulations. (2006). Council Regulation (EC) SI No. 1013/2006 of the European Parliament and of the Council of 14 June 2006 on shipments of waste. Official Journal of the European Union, 190, 1.

[65] Landfill Directive. (1999). Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste. European Union directive issued on 16 July 2001.

[66] Department of Energy and Climate Change (DECC). (2011). Guidance Notes Decommissioning of Offshore Oil and Gas Installations and Pipelines under the Petroleum Act, version 6 (2011).

[67] Centrica Energy (2014) Centrica Guidance for Comparative Assessment Required for Decommissioning, CEU-HSEQ-GEN-GUI-0029, Rev C1, October 2013

[68] UKOOA. (2001) An analysis of UK Offshore oil and gas environmental surveys 1975 – 1995. Aberdeen: Heriot-Watt University, UKOOA.

[69] Buchanan, J.B. (1984). Sediment Analysis. In N.A. Holm, & A.D. McIntyre, Methods for the Study of Marine Benthos. London: Blackwell Scientific Publications.

[70] DECC (2014), National Atmospheric Emissions Inventory. The Scottish Government,

The Welsh Government and The Northern Ireland Department of the Environment Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland: 1990-2012, June 2014

[71] The Xerces Society for Invertebrate Conservation, (2014). Oil in our oceans. A review of the impacts of oil spills on marine invertebrates.

[72] Advisory Committee on Protection of the Sea (ACOPS) (2012) Annual survey of reported discharges attributed to vessels and offshore oil and gas installations operating in the United Kingdom pollution control zone, on behalf of the Maritime and Coastguard Agency.


[73] P. H. Kvaldsheim and E. M. Sevaldsen, “The potential impact of 1-8 kHz active sonar on stocks of juvenile fish during sonar exercises. Forsvarets Forskningsinstitutt (Norwegian Defence Research Establishment). FFA/RAPPORT-2005/01027.,” 2005.

[74] D. Ross, Mechanics of Underwater Noise, New York: Pergamon, 1976.

[75] S. Wales and R. Heitmeyer, “An ensemble source spectra model for merchant shipradiated noise.,” Journal of the Acoustical Society of America, vol. 111, pp. 1211-1231, 2002.

[76] F. H. Jensen, L. Bejder, M. Wahlberg, N. A. Soto, M. Johnson and P. T. Madsen, “Vessel noise effects on delphinid communication.,” Marine Ecology Progress Series, vol. 395, pp. 161 - 175, 2009.

[77] R. M. Rolland, S. E. Parks, K. E. Hunt, M. Castellote, P. J. Corkeron, D. P. Nowacek, S. K. Wasser and S. D. Kraus, “Evidence that ship noise increases stress in right whales.,” Proceedings of the Royal Society Birds, 2012.

[78] A. de Robertis and N. O. Handgard, “Fish avoidance of research vessels and the efficacy of noise-reduced vessels: a review.,” ICES Journal of Marine Science, vol. 70, no. 1, pp. 34 - 45, 2013.

[79] R. B. Mitson and H. P. Knudsen, “Causes and effects of underwater noise on fish abundance estimation.,” Aquatic Living Resources, vol. 16, pp. 255-263, 2003.

[80] Fingas, M.F. 1999. The evaporation of oil spills: development and implementation of new prediction methodology. International Oil Spill Conference Proceedings 2999, No. 1, pp. 281-287.

[81] Hawkins, S. J., P.E. Gibbs, N.D. Pope, G.R. Burt, B.S. Chesman, S.Bray, S.V. Proud, S.K. Spenxe, A.J.Southward, and W.J. Langston. 2002. Recovery of polluted ecosystems: The case for long-term studies. Marine Environmental Research 54(3):215-222.

[82] Kingston, P.F. 2002. Long-term environmental impact of oil spills. Spill Science & Technology Bulletin 7(1):53-61.

[83] Moore, J. 2006. Long term ecological impacts of marine oil spills. In 2006 Interspill Conference, Pembrokeshire, UK, 21-23 pp. London: Interspill, Ltd.

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[86] Peterson, C. H., S. D. Rice, J.W. Short, D. Esler, J. L. Bodkin, B.E. Ballachey, and D. B. Irons. 2003. Long-term ecosystem response to the Exxon Valdez oil spill. Science 302(5653): 2082-2086.

[87] IOP (2000) Guidelines for the calculation of Estimates of Energy Use and Gaseous Emissions in the Decommissioning of Offshore Structures, published by Institute of Petroleum, Feb 2000


APPENDIX A – ENVIRONMENTAL WORKSHOP OUTPUT

Centrica Mitigations, Controls a

Existing controls - Industry Standard, Legislative or

Prescriptive

Initial Ranking following controls and mitigation

Impact

Probability (Likelihood)

Rank

of Environmental Impact Description

1. Administrative or Procedural Controls

2. Engineering or Physical Controls

Co

nse

qu

ence

(S

ever

ity)

Du

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on

/Fre

qu

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Pro

bab

ility

(L

ikel

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)

Init

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Project Specific and Centrica Best Practice

missions to atmosphere radation of local/regional air particulates). Trans boundary

ontributing to global warming (CO2);

1. Normal shutdown procedures e.g. permit to work, operating instructions. Mining permit covers all venting. 2. Existing controls for the Markham Platform shutdown. Tanks for liquids, Hoses

0 1

Blowdown to J6 - normaoperation for shutdown.Optimal to put gas to theMarkham Platform and

process rather than ventInventory expected to besmall as production hasstopped. Tank to captureliquids on the Markham

Platform. Water may contain heavy metals anNORM. Anticipated to be

few metres cubed of mixehydrocarbon and water a

per shutdown.

d discharge to sea e marine ecosystem. Organic

chemical contaminant effects mn and seabed sediments

2 2

missions to atmosphere radation of local/regional air particulates). Trans boundary ontributing to global warming

(CO2);

1 2


(CO2); 1. Procedures for opening vessels

as possible NORM (and heavy metal) contamination.

2. Tanks on the Markham Platform

to contain material returned.

1 2

Assess to see where lowpoints in the system whicwill provide an idea wher

residues could remain.Treat all process pipes a

if contaminated with NORM and heavy metals



1 2

d discharge to sea mmediate vicinity of discharge

ced, but effects are usually y rapid dilution in massive

of water; planktonic organisms e receptor. NORM impacts?

1 2

d discharge to sea rease in suspended solids in nd on seabed with potential to ical chemical characteristics of the seabed.

1. Changes to pipework and installation of temporary equipment may result in an increased potential

for releases, particularly during flushing activities. Assess on an equipment by equipment basis.

Procedures for installation of temporary equipment.

1 3



Prescriptive


Impact


Rank




Co

nse

qu

ence

(S

ever

ity)

Du

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on

/Fre

qu

ency

Pro

bab

ility

(L

ikel

iho

od

)

Init

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/ Im

pac

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ng




of water; planktonic organisms vulnerable receptor.

1. Maximum volume of 2 litres per core in the umbilical (4 cores)

2. Operational permit (Permit to

Work and TBT) for the discharge and valve operation

1 1

The content of the umbilical will be displace

to the topsides and shipped to shore.

Therefore only a small amount of methanol andCI may be discharged to

sea when the flushing loops are installed. Durinthis operation the valves

the topsides umbilical termination unit will be

closed to contain the heatherefore limiting

discharge. This will be controlled through lock

valve procedures.



1 3



of water; planktonic organisms e receptor. NORM impacts?

1. The discharges from Stamford will

be permitted, Term OPPC and MAT/SATs. Chemical use and discharge from the Markham Platform will be covered by

environmental mining permit. There will be Chemical Management on

the Markham Platfom and standard operating procedures.

1 1

There will be a cold vent air (in Nl sector) when pi

receiver installed. This can't go into the processsystem as it is at a highepressure. The pipeline w

be pigged towards the platform. There will be a

requirement for some discharge to sea at pig laucher. Ensure that

samples are taken and analysed NORM (all item

returned to the vessel what could be contaminated).



1 2

missions to atmosphere radation of local/regional air particulates). Trans boundary


1 1

ds deposit to sea spended solids in the water lution and dispersion before ttling on seabed.

1 1



Prescriptive


Impact


Rank




Co

nse

qu

ence

(S

ever

ity)

Du

rati

on

/Fre

qu

ency

Pro

bab

ility

(L

ikel

iho

od

)

Init

ial R

isk

/ Im

pac

t R

anki

ng


to seaExcessive increase in lids in water column and on tential to change the physical aracteristics of the seabed.

1 2


ced, but effects are usually y rapid dilution in massive f water ; planktonic organisms vulnerable receptor.

Chemical use will be incompliance with the OCR.

1 1



1 3


1 1

ds deposit to sea ase in suspended solids and/or marine ecosystem. Organic chemical contaminant effects mn and seabed sediments

1 3


The removal of the infrastructure will all be proceduralised to minimise

deposits to the sea. 1 1

to sea Excessive increase in lids in water column and on tential to change the physical aracteristics of the seabed.

The removal of the infrastructure will be proceduralised to minimise the

deposits to the sea. Trials for dismantling of the WHPS have been undertaken onshore to ensure the feasibility of the operations. Trials

have minimised the likelihood for the requirement for cutting.

1 2

Noise in air difications to birds and marine

mammals, 1 1



Prescriptive


Impact


Rank




Co

nse

qu

ence

(S

ever

ity)

Du

rati

on

/Fre

qu

ency

Pro

bab

ility

(L

ikel

iho

od

)

Init

ial R

isk

/ Im

pac

t R

anki

ng


ds deposit to sea ocio-economic impact e.g. to

ential to change the physical abitat characteristics of the

ensive seabed disturbance gnificant community change. nd extent dependent on type of pecies present and location ate within the relevant EIA. l/sub-lethal effects on benthic fauna from physical abrasion; hering of organisms following of resuspended particles.

1. Covers the possibility of dropping sections of the subsea structure.

Trials for dismantling of the WHPS have been undertaken onshore to

ensure the feasibility of the operations.

1 3

e use - Physical Area ysical seabed disturbance

munity change. Recovery time endent on type of seabed and and location specific estimate

evant EIA. Lethal/sub-lethal hic and epibenthic fauna from on; Smothering of organisms

ment of re-suspended particles.

1 1

mission to atmosphere radation of local/regional air particulates). Trans boundary ontributing to global warming

(CO2);

1. Damage to wellhead 3 3

Guard vessel over wellhead once the WHPShas been removed andbefore the rig arrives on

site. ds deposit to sea spended solids in the water lution and dispersion before

biodegradation.

1.Jetting marine growth off connection points underwater with HP water jets. Recover to vessel

deck and wash down on deck. Tree will be cleaned with HP water jet for

rig to have access.

2. Jetting procedures - part of lifting procedures or tree cleaning

procedures.

1 1



Prescriptive


Impact


Rank




Co

nse

qu

ence

(S

ever

ity)

Du

rati

on

/Fre

qu

ency

Pro

bab

ility

(L

ikel

iho

od

)

Init

ial R

isk

/ Im

pac

t R

anki

ng


arge to seaWater quality in y of discharge will be reduced,

e usually minimised by rapid sive receiving body of water; sms most vulnerable receptor.

1 1

ds deposit to sea spended solids in the water lution and dispersion before ng on the seabed.

1. Possibility for a requirement for localised jetting to clear sediment and rock away to access umbilical prior to reverse reel. The jetting will

be proceduralised to minimise disturbance, and avoided if possible.

1 2

ds deposit to sea rease in suspended solids in nd on seabed with potential to ical chemical characteristics of the seabed.

1 3

ds deposit to sea 1. Need to lower the umbilical from the J-tube. This may require the

umbilical to be laid on the seabed, prior to recover. Procedure will be

prepared that will minimise disturbance.

2. Dropped object

1 1

ds deposit to sea

1 3

d discharge to sea 1. The umbilical may contain relatively small quantities of residual chemical which may be released to

sea when the umbilical is moved from the J-tube.

2. Flushing procedures

1 3

e Use - Physical Area 1. Need to lower the umbilical from the J-tube. This may require the

umbilical to be laid on the seabed momentarily as pulled up and over

mattresses that will still be in position.

2. Within 500 m and will be handed back.

3. Lifting procedures, stakeholder register

1 1



Prescriptive


Impact


Rank




Co

nse

qu

ence

(S

ever

ity)

Du

rati

on

/Fre

qu

ency

Pro

bab

ility

(L

ikel

iho

od

)

Init

ial R

isk

/ Im

pac

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anki

ng


ds deposit to sea 1. Disruption to the seabed (as some natural backfill of the trench will have occurred) the umbilical

sections are lifted out of the trench, though the water column and onto

the back of the vessel. (The section within 500 m and will be left in place as it is under the same mattresses

as the flexible riser for which there is an opportunity for reuse. It will be removed at the same time as the flexible riser.) Unlikely potential

unplanned deposits to sea include dropping the umbilical or snapping the umbilical. For both they will be

recovered. 2. Procedures, analysis prior to work offshore. Work packs, HAZIDs and

HIRAs etc.

1 2 Analysis to establish if jetting of the rock and

burial is required.

ds deposit to sea

1 2

ds discharge to sea 1. Discharge from the umbilical as it is being lifted from the seabed.

Residues and chemicals left in the umbilical will have been permitted

on the SAT/MAT. Possible leakage of hydraulic fluid (aquaglycol).

1 2


1 2

Noise in water arm, behavioural modifications als, turtles and potentially fish.

cts due to cumulative impact or roductively significant number ividuals or location.

1. Cutting locations and procedures indented to minimise the number

and duration of cutting.

2. Cutting locations and procedures indented to minimise the number

and duration of cutting.

1 1

Cutting tool selected onthe technical capability,

mechanical cutters, likelyto be selected which alsoare likely to be quieter.

Noise in water siological harm, behavioural marine mammals, turtles and

potentially fish. cts due to cumulative impact or

1 2



Prescriptive


Impact


Rank




Co

nse

qu

ence

(S

ever

ity)

Du

rati

on

/Fre

qu

ency

Pro

bab

ility

(L

ikel

iho

od

)

Init

ial R

isk

/ Im

pac

t R

anki

ng


roductively significant number ividuals or location.


chemical contaminant effects mn and seabed sediments. ; sms most vulnerable receptor. ORM impacts?

1. Any liquid/hydrocarbon left after flushing/cleaning. Retrieved with both ends open - water moving

through. Pipeline sections will drain as they are lifted through the water

column. 2. Chemical use and discharge will

have been permitted during the flushing and cleaning process. OPPC permit for hydrocarbon

residues. Pigging will have been undertaken.

1 3

OPPC permit - estimatevolume from volume of pipe - planned activity.Likely residues will be

assessed following flushing and cleaning.

Controlled through liftingprocedures. Dropped

objects will be recovered


1. Suspension of sediment when lifting (no cuttings pile)

2. Controlled through lifting procedures.

1 1


1. Suspended solids from dropped objects interaction with the seabed.

2. Controlled through lifting procedures. Dropped objects will be

recovered.

1 2

t to seaNavigation or socio-ct e.g. to fisheries. Potential to hysical chemical or habitat

cs of the seabed. Extensive bance resulting in significant nge. Recovery time and extent type of seabed and species

cation specific estimate within A. Significant lethal/sub-lethal hic and epibenthic fauna from ion; Extensive smothering of ing settlement of resuspended

particles.

1. Dropping of the pipelines and spools

2. Controlled through lifting procedures. Dropped objects will be

recovered.

1 2



Prescriptive


Impact


Rank




Co

nse

qu

ence

(S

ever

ity)

Du

rati

on

/Fre

qu

ency

Pro

bab

ility

(L

ikel

iho

od

)

Init

ial R

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/ Im

pac

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anki

ng



1. Suspension of sediment when lifting (no cuttings pile)

1 1


1. Jetting of pipeline ends only as contingency.

2. Procedures and workpacks. A dredging tool suitable for the size of job will be used to ensure that only

the area that requires to be dredged will be disturbed.

1 1

Jetting tool will be selecteto be the correct size an

type to undertake the work.

ds deposit to sea ocio-economic impact e.g. to

ential to change the physical abitat characteristics of the

ensive seabed disturbance gnificant community change. nd extent dependent on type of pecies present and location ate within the relevant EIA. l/sub-lethal effects on benthic fauna from physical abrasion; hering of organisms following of resuspended particles.

1. Jetting (only as a contingency) of an area larger than required to lower

the ends of the pipeline. 1 3

emissions to atmosphere local/regional air quality (NOx ). Trans boundary air pollution. to global warming (CO2);

1. Dependent on disposal options selected e.g. treatment, incineration.

Heavy metals and NORM. 2. Waste inventory - EU waste

catalogue - will highlight hazardous materials (needed for transportation

information etc.). Possible quarantine of NORM or heavy metal

contaminated equipment on the vessel for segregation - minimise

cross contamination.

1 2


(CO2);

1. Dependent on disposal options selected e.g. treatment. Include

knock on impacts of liquid discharge to sewer.

1 3



Prescriptive


Impact


Rank




Co

nse

qu

ence

(S

ever

ity)

Du

rati

on

/Fre

qu

ency

Pro

bab

ility

(L

ikel

iho

od

)

Init

ial R

isk

/ Im

pac

t R

anki

ng


charge to surface water mmediate vicinity of discharge

ced, but effects are usually pid dilution in receiving body of

water.

1. Cutting onshore. 1. Dependent on disposal options

selected e.g. treatment - hazardous landfill might be needed

2. Waste Management Plan. Waste handling and transportation procedures. Offshore waste

management procedure in place. Waste segregated to allow recycling

where possible. Quantification of waste (waste disposal company

permitting). Transportation company and vessel master may need

certificate before to ensure not hazardous for transportation - proof

before shipping. Licenced waste management site.

3. Waste segregation and minimisation of waste by design of the operation. Including pigging.

1 2

charge to surface water e marine ecosystem. Organic

chemical contaminant effects column and sediments.

1 3

Noise in air o commercial / residential neighbourhood

1 1

Noise in air o commercial / residential neighbourhood

1 3

d deposit to land l and landfill resource take 1 2

d deposit to land of landfill and landfill resource

take 1 3

local/regional air quality (NOx ). Trans boundary air pollution. g to global warming (CO2);

1. Temporary during preparation activities. Temporary equipment e.g.

diesel generators for flushing and cleaning and well kill. Also required

for onshore waste disposal, e.g. cutting prior to loading onto

transportation.

2. Centrica Assurance of contractor

1 2

radation of local/regional air particulates). Trans boundary


1 3

ource use - energy ate change and reduction of ces of hydrocarbons

1 2



Prescriptive


Impact


Rank




Co

nse

qu

ence

(S

ever

ity)

Du

rati

on

/Fre

qu

ency

Pro

bab

ility

(L

ikel

iho

od

)

Init

ial R

isk

/ Im

pac

t R

anki

ng


ource use - energy pact on climate change and resources of hydrocarbons

equipment/maintenance procedures

1 3

Physical areaDisturbance of within the recovery estimate calised seabed disturbance

munity change. Recovery time ndent on type of seabed and and location specific estimate vant EIA. Lethal/sub-lethal ic and epibenthic fauna from

on; Smothering of organisms ent of resuspended particles.

1. Debris survey after removal.2. After removal the over trawling will sweep seabed to check for snag

hazards. 3.Coarse sediments and dynamic water currents also

encouraging sediment movement.

1 2

the ecosystem exceeding timate in the EIA. Extensive ance resulting in significant ge. Recovery time and extent type of seabed and species ation specific estimate within . Significant lethal/sub-lethal ic and epibenthic fauna from on; Extensive smothering of ng settlement of resuspended

particles.

1 3

e use - Physical Area al and return of seabed to pre-us for socioeconomic use e.g.

fishing

1. Removing the safety zone for e.g. fishing and wind farm use. Confirm depth of burial of pipeline.

1 2

e use - Physical Area are able to have complete use avigation and not confined by nfrastructure

1. Removing the safety zone. Depth of burial survey and pipeline

conditions survey - will demonstrate if infrastructure buried or not. Post

decommissioning surveys will review the status of the infrastructure burial. If surveys show rest of pipeline has

remained buried then end of pipeline is likely to remain buried.

1 2

e use - Physical Area are unable to have complete or navigation and continue to

nfrastructure longer and/or for r area than estimated

1 3



Prescriptive


Impact


Rank




Co

nse

qu

ence

(S

ever

ity)

Du

rati

on

/Fre

qu

ency

Pro

bab

ility

(L

ikel

iho

od

)

Init

ial R

isk

/ Im

pac

t R

anki

ng


e use - Physical Area bed disturbance resulting in nt community change.

1 3

e use - Physical Area gation longer than expected - ghtly different location

1 3

ischarge to the sea marine ecosystem. Organic chemical contaminant effects mn and seabed sediments

1 3


APPENDIX C – OPEP MODELLING




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