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LETTERKENNY REGIONAL WATER SUPPLY SCHEME
AND CREESLOUGH WATER TREATMENT PLANT
OUTLINE METHOD STATEMENT FOR BUNLIN RIVER
CROSSING AT BUNLIN, MILLFORD, COUNTY DONEGAL
Letterkenny Regional WSS and Creeslough WTP Outline Method Statement for Crossing at Bunlin Bridge
Nicholas O’Dwyer Ltd. i November 2015
IRISH WATER
LETTERKENNY REGIONAL WATER SUPPLY SCHEME AND
CREESLOUGH WATER TREATMENT PLANT
OUTLINE METHOD STATEMENT FOR BUNLIN RIVER CROSSING AT
BUNLIN, MILLFORD, COUNTY DONEGAL
Nicholas O’Dwyer Ltd.,
Consulting Engineers,
Nutgrove Office Park,
Nutgrove Avenue,
Dublin 14. November 2015
PROJECT NO. 20579
Revision Reason for Revision Prepared by Reviewed by Approved by Issue Date
- First Issue T.Farrell
K.Hanna
C.Sheehan
G.Chanie T.Farrell 20/11/2015
A Foreshore Licence Application
Revision K.Hanna G.Chanie
T.Farrell 18/02/2016
B Removal of Construction Details for
Foreshore Licence Application K.Hanna G.Chanie
T.Farrell 12/05/2016
C
D
Letterkenny Regional WSS and Creeslough WTP Outline Method Statement for Crossing at Bunlin Bridge
Nicholas O’Dwyer Ltd. ii November 2015
CONTENTS
1. INTRODUCTION 3
1.1 Background of Project 3
1.2 Impact on Mulroy Bay SAC 3
2. PIPELINE DESIGN 5
2.1 Design Overview 5
2.2 Construction Technique Error! Bookmark not defined.
2.2.1 Selection of Construction Technique Error! Bookmark not defined.
2.2.2 Details of Construction Technique Error! Bookmark not defined.
3. ENVIRONMENTAL IMPACT 9
3.1 Environmental Considerations 9
3.2 Dewatering Excavations: Impacts and Mitigation 10
Letterkenny Regional WSS and Creeslough WTP Outline Method Statement for Crossing at Bunlin Bridge
Nicholas O’Dwyer Ltd. 3 November 2015
1. INTRODUCTION
1.1 Background of Project
The principal objective of the overall Letterkenny Regional Water Supply Scheme project
is to provide drinking water in compliance with the Drinking Water Regulations to all
consumers within the Letterkenny Regional Water Supply Scheme (LRWSS), including
Church Hill, Creeslough and Rathmelton / Rathmullan.
Part of the scheme involves the extension of the Cranford WTP water distribution
network to Millford to transfer treated water to Millford Town Reservoir. The proposed
route of the watermain will entail crossing the Bunlin River at Bunlin road bridge. This
report details the design proposals for attaching the pipeline to the road bridge in order
to minimise the impact on the surrounding environment.
1.2 Mulroy Bay SAC
It is intended that the proposed pipeline from the Cranford WTP network to Milford town
will be routed along the R245 as it crosses the Mulroy Bay SAC for a length of
approximately 150 metres near the mouth of the estuary as shown in Figure 1. The
details of the works involved are described in Section 2 below. An Appropriate
Assessment Screening Report has been completed for the works to determine impacts (if
any) on the SAC and its qualifying interests.
Letterkenny Regional WSS and Creeslough WTP Outline Method Statement for Crossing at Bunlin Bridge
Nicholas O’Dwyer Ltd. 4 November 2015
Letterkenny Regional WSS and Creeslough WTP Outline Method Statement for Crossing at Bunlin Bridge
Nicholas O’Dwyer Ltd. 5 November 2015
2. PIPELINE DESIGN
2.1 Design Overview
It is proposed to route a 180mm OD HDPE 10 bar watermain along the R245 roadway
corridor through to Milford Reservoir. Bunlin Bridge is located where the road crosses
the foreshore area and Mulroy Bay SAC close to where the Bunlin River meets the
Mulroy Bay. It is proposed to fix the pipework and supporting steel beams to the
existing road bridge.
• The first option considered was to drill the pipeline under the bed of the river
10 metres upstream of the road bridge.
• A second option involving the fixing of the pipeline to the road bridge
structure was identified and which would be advantageous in terms of
reducing the environmental impact.
• An outline design was forwarded to Donegal County Council for their
consideration. The Donegal County Council Roads Department have
responded to advise that there would be no objection in principle.
• In summary,
- the pipeline will deviate off the carriageway on either side of the road
bridge structure.
- The pipeline will be fixed to the steel beams within 300mm of the
concrete deck.
Mitigation measures relating to construction works, which form part of the design
requirements, are detailed in Section 3 of this method statement.
Letterkenny Regional WSS and Creeslough WTP Outline Method Statement for Crossing at Bunlin Bridge
Nicholas O’Dwyer Ltd. 9 November 2015
3. ENVIRONMENTAL IMPACT
3.1 Environmental Considerations
Mulroy Bay SAC includes the foreshore area. In addition, Inland Fisheries Ireland has
designated the Bunlin River as a Sea Trout habitat.
The major adverse effects associated with the excavation works required for construction
in close proximity to river channels will most likely be related to run-off creating localised
elevations in suspended solids in the river course. Erosion of river banks and subsequent
impacts on water quality together with the siltation of substratum have been identified
as a threat to the gills of the sea trout and aquatic fauna if deposited on the river
substratum.
Without careful design, appropriate mitigation and supervision, the construction-related
works associated with the pipe bridging could have the potential to contaminate surface
water bodies due to spillages of concrete, fuels and chemicals etc.
Mitigation measures appropriate to prevent the adverse effects associated with sediment
run-off, spillages of chemicals such as fuels, oils and cement associated with the
construction works are detailed below. These measures represent best practice in
reducing the risks/lessening the effects due to construction works on river water quality
and sensitive receivers. The Contractor nominated to carry out the works will be required
to ensure the works will follow good site practice in accordance with Section 3 of the
Local Government (Water Pollution) Act, 1977 which states a general prohibition on the
entry of polluting matter to waters. It is also considered that full time supervision will
be provided for the duration of the construction works who will have the authority to
stop construction activities where unapproved work practices are found to be taking
place.
A summary of mitigation measures adopted by Inland Fisheries Ireland for the protection
of salmonid rivers in Ireland will be used in the first instance to establish a baseline
standard for mitigation measures. These will be further developed and tailored to each of
the specific construction related activities. The IFI Guidance Notes provide
recommendations to minimise run-off/suspended matter in river courses.
• River banks should be left as intact and all practicable measures should be
taken to prevent soils from entering the Bunlin River.
Letterkenny Regional WSS and Creeslough WTP Outline Method Statement for Crossing at Bunlin Bridge
Nicholas O’Dwyer Ltd. 10 November 2015
• Fuels, oils, greases and other potentially polluting chemicals must be stored
in bunded compounds at least 50m away from the river. Any fuels, oils or
chemicals will be stored on impervious bases and adequately bunded to
100% of the total volume stored.
• A site induction will be required to brief contractors on the need for
environmentally-responsible working practices prior to any site work. The site
induction will include appropriate training for construction staff on how to
respond to accidental spillages of chemicals including oils on site.
• Spill kits and method statements for dealing with accidental spillages will
need to be provided. Any refuelling and maintenance of equipment will be
within contained areas and at least 50m from the river.
• Bunds of an impermeable material (i.e. clay) will be placed at excavation
edges where appropriate in order to prevent surface run-off entering the
excavations. This will reduce the amount of sediment laden run-off produced
by the excavations and any dewatering that may be required.
• Any runoff will be routed to via triple layered silt fences which will be
inspected regularly and maintained. No discharges of accumulated water from
the excavations will be made directly to the river.
• Stockpiles of material (e.g. sands, gravel, topsoil) shall be kept to a
minimum, kept covered when not in use and maintained at least 25m from
the river. Any excess excavated soil will be removed off site to a suitable
licensed site as soon as reasonably practicable.
3.2 Dewatering Excavations: Impacts and Mitigation
The main risk to the survival of the fish life and aquatic fauna is the potential for silt and
sediment to enter the Bunlin River.
The pumping out of groundwater untreated into the Bunlin River could have significant
adverse effects on the natural habitats. It will therefore be necessary to provide a
number of filtration/silt ponds or a water settlement tank prior to discharge to the river.
Detailed method statements for the construction and operation of the silt ponds and/or
water settlement tanks will need to be submitted to the Employer’s Representative prior
to works commencing on site.
Letterkenny Regional WSS and Creeslough WTP Outline Method Statement for Crossing at Bunlin Bridge
Nicholas O’Dwyer Ltd. 11 November 2015
Table 3.2 Impacts Associated with Surface Water/Dewatering
No. Construction Risks No. Mitigations
1
2
Potential risk of water entering the
Bunlin River from excavations. Risk of
contamination with silt and fine
particles.
Heavy rainfall events could lead to the
runoff of silt and sediment from the
works site into the River putting the
mussel population at risk.
1
2
All water from the abutment excavations
will be pumped to a filtration pond or a
water settlement tank which will allow for
settlement and treatment.
Works area will be surrounded with silt
fencing and straw bales to absorb any
runoff. Stockpiled material will be stored
away from the River.