Bunlin - method statement

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


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


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.



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.



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.



• 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.



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.

Bunlin - method statement

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