Table of contents - Silverbirch Wind Farmsilverbirchwindfarm.com/wp-content/uploads/2017/04/... · 2017. 4. 6. · Hydrogeology. • Recommendations regarding mitigation measures

Table of contents

7 HYDROLOGY AND HYDROGEOLOGY ........................................................................ 7-1

7.1 Introduction .................................................................................................................. 7-1

7.2 Existing Environment ..................................................................................................... 7-1

7.2.1 Overview of Existing Environment ..................................................................................................... 7-1

7.2.2 Hydrology ........................................................................................................................................... 7-2

7.2.3 Soils and Bedrock Geology ................................................................................................................. 7-5

7.2.4 Hydrogeology ..................................................................................................................................... 7-5

7.2.5 Aquifer Vulnerability .......................................................................................................................... 7-6

7.2.6 Groundwater Wells ............................................................................................................................ 7-6

7.2.7 Rainfall and Evaporation .................................................................................................................... 7-6

7.2.8 Flood Hazard ...................................................................................................................................... 7-6

7.3 Likely Significant Impacts ............................................................................................... 7-8

7.3.1 Construction Stage Impacts ............................................................................................................... 7-8

7.3.2 Operational Stage Impacts ............................................................................................................... 7-13

7.3.3 Cumulative Impact ........................................................................................................................... 7-14

7.4 Mitigation .................................................................................................................... 7-15

7.4.1 Construction Stage Mitigation Measures ......................................................................................... 7-15

7.4.2 Operational Stage Mitigation Measures .......................................................................................... 7-21

7.4.3 Decommissioning Phase Mitigation Measures ................................................................................ 7-21

7.4.4 Monitoring ....................................................................................................................................... 7-22

7.5 Residual Impacts .......................................................................................................... 7-22

7.6 Conclusion ................................................................................................................... 7-23

17924-6001-A Water and Hydrology March 2017

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7 HYDROLOGY AND HYDROGEOLOGY

7.1 INTRODUCTION

O’Callaghan Moran & Associates (OCM) were engaged by Silverbirch Renewables Ltd. to assess the

potential impacts of the proposed Silverbirch Wind Farm development on the Soils, Geology,

Hydrology and Hydrogeology of the subject area. This chapter has been completed by Malone

O’Regan (MRG) and updated by MWP, and is largely based on the OCM report. The scope of their

assessment included:

• Site Inspection completed in February 2016

• Review of the results of the Geophysical Survey of the site undertaken by Apex

Geoservices Ltd. as detailed in Volume 3, Appendix 6B, Apex Report, of this EIS.

• Review of further planning stage geotechnical investigations and Soils and Geology

Assessment undertaken by MRG Consulting Engineers Limited as detailed in Volume 3,

Appendix 6A, MRG Soils and Geology Assessment of this EIS.

• Review of databases maintained by the Geological Survey of Ireland (GSI), the

Environmental Protection Agency (EPA), Teagasc, Met Eireann and the South Western

River Basin Management Plan.

• Assessment of potential impacts of the proposed Wind Farm development on the

geology, hydrogeology and hydrology of the area. The assessment of impacts had regard

to the National Roads Authority (NRA) Guidance 2008 which is recommended by the

Institute of Geologists of Ireland to assessment impacts on Soils, Geology and

Hydrogeology.

• Recommendations regarding mitigation measures which might be implemented to

address any potential negative impacts.

A copy of OCM’s Report ‘Hydrological and Hydrogeological Impact Assessment Proposed Silverbirch

Wind Farm, Co. Kerry’ is included in Volume 3, Appendix 7A of this EIS.

Sections of the Ecological Impact Assessment (EcIA) completed by Ecofact Environmental

Consultants for the subject development, as included in Volume 3, Appendix 5A, and detailed in

Chapter 5 of this EIS, and which deal with aquatic ecology, are also relevant to this section of the EIS,

and are referenced as appropriate.

A Surface Water Management Plan (SWMP) has been prepared for Silverbirch Wind Farm (see

Appendix 7B, Volume 3 of the EIS). The purpose of the plan is to set out the procedures and control

mechanisms that need to be put in place in order to prevent sediment pollution of the downstream

watercourses. The SWMP as designed and engineered will ensure that all contaminated water will

be collected and treated before being discharged to the downstream watercourses.

7.2 EXISTING ENVIRONMENT

7.2.1 Overview of Existing Environment

The proposed Silverbirch Wind Farm site is located on elevated ground close to the watershed of the

Blackwater and Laune River catchments. It is noted that proposed turbines T3, T6, T7 and their

17924-6001-A Hydrology and Hydrogeology March 2017

7-2

associated infrastructure are located close to the nominal divide between the Blackwater and Laune

catchments but that all drainage from these areas will be directed towards the Blackwater

catchment. All other turbines and the remaining Wind Farm infrastructure are clearly within the

Blackwater catchment with one exception, a stretch of new road approximately 120 m in length

which will be used as a temporary access link to an existing track that leads to borrow pit one.

Figure 7-1. Catchment map showing turbine locations

A hydrological overview of each catchment is presented below. The primary focus is on the

watercourses within the Blackwater catchment potentially affected by the proposed development.

The Laune catchment has been included on the basis that parts of the overall development

boundary for the Wind Farm fall within this catchment, although as noted, the majority of the

drainage serving the Wind Farm infrastructure will be to the Blackwater catchment.

The Hydrological and Hydrogeological Impact Assessment prepared by OCM also identifies relevant

information in relation to soils, bedrock geology, hydrogeology, groundwater wells and meteorology

of the study area as appropriate, as outlined below.

7.2.2 Hydrology

7.2.2.1 Blackwater Catchment

The River Blackwater (EPA code 18B02) rises in east Co. Kerry approximately 6.5km north west of

Ballydesmond. The river flows east for approximately 170km through the counties of Cork and

Waterford flowing through Ballydesmond, Banteer and Mallow before entering the sea at Youghal.

Its entire catchment is in the region of 3,100km2. It drains five ranges of mountains, and in times of

heavy rainfall can fluctuate by more than four meters. The peaty nature of the terrain in the upper

reaches and some of the tributaries gives the water a dark colour, hence the river’s name.


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A stretch of approximately 6km of the upper reaches of the Blackwater River flow within 2km of the

proposed development. Drainage from the proposed development is to the Blackwater River either

directly or via the streams that connect the site to this river. There are three 2nd order streams

draining the proposed development that flow into the Blackwater River from the east. From north to

south (upstream to downstream) these are the Carhoonoe Stream, the Mountinfant Stream and the

Reanasup Stream.

The Carhoonoe Stream (EPA code 18C87; also known as the Yellow River) rises near the watershed

of the Maine and Blackwater catchments. It flows roughly 3km in an easterly direction across the

proposed development site, joins the 2nd order Tooreengarriv Stream (EPA code 18T27) and an

unnamed stream to the south, and subsequently flows ca. 2km south east to join the Blackwater ca.

1km upstream of Newquarter Bridge (EPA station code 18B02 0075).

To the south of the Carhoonoe Stream lies the Mountinfant Stream (EPA code 18M55). The

Mountinfant stream flows for ca. 2km in an easterly direction before it is joined from the south by

another 1st order stream of similar size at Tooreencahill (EPA code 18T30). The 2nd order

Mountinfant stream then flows for ca. 2km in an easterly direction into the Blackwater ca. 1km

downstream of Newquarter Bridge.

The Reanasup Stream (EPA code 18R44) rises within the proposed development site. This 1st order

stream flows south east over a length of ca. 1km and it is met from the east by another 1st order

watercourse (EPA code 18R25). After the confluence of these two streams, the Reanasup stream

flows east for ca. 1km and joins the River Blackwater approximately 2.8km downstream of

Newquarter Bridge.

All mapped streams associated with the site and within the catchment have been classed as having

Good ecological status under the Water Framework Directive. Biological water quality sampling of

the streams within the site ranged from moderate (Q3-4) to high (Q5) water quality (see the

Ecological Impact Assessment report in Appendix 5A, Volume 3).


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Figure 7-2. Map showing Wind Farm infrastructure and watercourses


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7.2.2.2 Laune Catchment

The River Laune (EPA code 22L01) is a river in County Kerry which flows from Lough Leane (one of

the Lakes of Killarney), through the town of Killorglin, and empties into the sea at Castlemaine

Harbour within Dingle Bay.

It is indicated by the EPA River Catchment data layer that T3, T6 and T7 are sited partially in the

Laune catchment, but drainage will be directed east to the Blackwater River. The Quagmire River

rises in the townland of Tooreennamult to the west of the proposed development. The Quagmire

River is joined from the west by a 1st order unnamed 1st order stream approximately 0.5km from its

source. The Quagmire River flows south for ca. 1km before being joined by the 1st order

Tooreenamult Stream (EPA code 22T32). The Tooreenamult Stream has a channel length of ca.

1.5km. T6 and T7 border the Laune catchment drained by the Tooreenamult Stream which is located

approximately 0.5km to the west.

A small component of the south western extent of the proposed development is drained by the

Mausrower Stream (EPA code 22M21). The Mausrower Stream rises in the townland of

Knocknageeha approximately 750m from proposed turbine T3. This stream flows for ca. 1.5km south

west as a 1st order watercourse before being met by a 1st order stream (segment code 22_1428) of

ca. 1km long from the north. The Mausrower Stream continues to flow west for 1km before meeting

the Quagmire River (EPA code 2Q01).

On its southerly course to Headford, over a channel length of ca. 15km, the Quagmire River is fed by

numerous other tributaries, including the Mausrower Stream (EPA code 22M21), the Knockrower

East Stream (EPA code 22K32), the Annaghghilymore River (EPA code 22A28), the Annaghghilymore

Stream (EPA code 22A03), the Meentoges Stream (EPA code 22M05) and the Beeheenagh River (EPA

code 222B01). Thereafter, the 4th order Quagmire River (Owneykeagh River, EPA code 22O25)

generally flows south west to meet the River Flesk (EPA code 22F02) ca. 2km upstream of Flesk

Bridge.

All streams in this part of the catchment have been classed as having Good ecological status under

the Water Framework Directive. Biological water quality sampling of the streams ranged from

moderate (Q3-4) to good (Q5) water quality (see the Ecological Impact Assessment report in

Appendix 5A, Volume 3).

7.2.3 Soils and Bedrock Geology

As detailed in Chapter 6 (Soils and Geology) of this EIS and in Section 2.2 of the OCM Report (see

Volume 3, Appendix 7A), the Teagasc Map for the area indicates that the overburden across the

proposed Silverbirch Wind Farm site comprises blanket peat and is generally underlain by glacial till,

commonly described as boulder clay. The till comprises shale and sandstone gravels, cobbles and

boulders in a silty clay matrix. The underlying bedrock comprises Namurian shales and sandstones.

7.2.4 Hydrogeology

The bedrock comprises Namurian sediments that are characterised by the GSI as Locally Important

Aquifers that are productive only in local zones (Ll) (Figure 2.7 and 2.8). In this type of aquifer the

transmissivity is likely to range from 2 to 20 m2/d, with groundwater velocities of less than 1 m/day

and flow paths in the 10s to 100s of metres.


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The effective rainfall for the Ballydesmond area is 1252 mm/yr. The GSI recharge database indicates

that the recharge rate varies across the site depending on the composition of the subsoil, with an

average recharge of 15% (188 mm/yr) in the shale and sandstone derived till, and 4% (37.5mm/yr) in

the blanket peat areas. These recharge rates indicate that much of the incident rainfall will

preferentially run-off to the surface water system rather than enter the underlying bedrock aquifer.

Three borrow pits will be used during the construction phase, one in the northern section and two in

the southern part. It is likely that groundwater inflows during the excavation of the pits, which will

extend below ground level, will be very limited given the nature of the bedrock and the upland

location of the site.

In the northern section the direction of groundwater flow is expected to be toward the Yellow River

to the south and the Blackwater River to the east. In the southern part of the Wind Farm, the

groundwater flow will be generally from west to east toward tributaries of the Toreencahill Stream.

7.2.5 Aquifer Vulnerability

Vulnerability is a term used to represent the intrinsic geological and hydrogeological characteristics

that determine the ease with which groundwater may be contaminated by human activities, it is

largely controlled by the nature and thickness of the sub-soils.

Vulnerability categories are based on the geological and hydrogeological factors described above:

Extreme (E), High (H), Moderate (M) and Low (L). The GIS database and maps (Figure 7.9 and 7.10)

show the vulnerability classification in the vicinity of the project infrastructure is predominantly Low

(L).

7.2.6 Groundwater Wells

The GSI Well database has records of seven private wells within 1 km of the northern section and

eight wells within 1km of the southern part. All these wells are described as agriculture and

domestic use wells with generally low yields. It is likely that other unrecorded wells with similar use

exist in the area.

The site is located in the Rathmore West Groundwater Body (IE-SW-G-070). The Groundwater Body

(GWB) status as designated in the South Westerns River Basin District (SWRBD) Plan is currently

(2009 – 2015) is Good with the objective to protect the status. A copy of the GWB Report is included

in Appendix 1 of the OCM Report (see Volume 3, Appendix 7A of this EIS).

7.2.7 Rainfall and Evaporation

Long term 30-year rainfall and evaporation data was sourced from Met Eireann. The closest synoptic

station is Valentia. The 30 year average annual rainfall is 1558mm/yr. The effective rainfall for the

Ballydesmond area is 1,252 mm/yr.

7.2.8 Flood Hazard

The National Preliminary Flood Risk Assessment (PFRA) was reviewed to determine the risk of

flooding of the site. The mapping has been prepared on behalf of the Office of Public Works (OPW)

on a national scale as part of the Catchment Flood Risk Mapping (CFRAMS) project. The flood extent

maps were produced for various flood events of a given probability of occurrence. These are the

10%, 1% and 0.1% annual exceedance probability (AEP) events for fluvial flooding, which are

equivalent to the 1 in 10, 1 in 100 and 1 in 1,000 year flood events respectively.


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The Preliminary Flood Risk Assessment Maps for the area are presented in Volume 3, Appendix 7A,

Appendix 3, of OCM report. They show that none of the turbine sites, or met masts are located in

areas liable to flooding. Given the upland nature of the Wind Farm location flood risk is likely to be

low.


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7.3 LIKELY SIGNIFICANT IMPACTS

Potential impacts on water and hydrology associated with the construction, operational and

decommissioning phases of the proposed Silverbirch Wind Farm development have been identified

on the basis of the Hydrological and Hydrogeological Impact Assessment (HHIA) Report for the

project prepared by OCM and included in Volume 3, Appendix 7A of this EIS, as well as potential

impacts on aquatic habitats and ecology identified in the Ecological Impact Assessment (EcIA)

prepared by Ecofact Environmental Consultants and included in Volume 3, Appendix 5A.

7.3.1 Construction Stage Impacts

7.3.1.1 Forestry Felling

Felling of small areas of existing forestry plantation will be required to facilitate construction of the

Wind Farm.

The HHIA Report prepared by OCM identifies that felling operations have the potential to have a

short-term moderate impact on surface water quality and flow if not undertaken in accordance with

best practice. It can result in blockage of drains and streams and to excessive silt run-off due to

removal of vegetation near drains and streams. Measures will be required to mitigate potential

impacts on hydrology. Impacts on hydrogeology are not considered to be significant.

7.3.1.2 Site Establishment and Construction Compounds

As identified in Section 2.3 of this EIS, it is intended to establish two temporary construction

compounds to facilitate the construction of the Wind Farm. These will be located to the rear of the

Wind Farm Substation at Knocknageeha and at Ballynahulla between the existing site entrance off

the R577 Regional Road and Borrow Pit No. 3.

The works associated with the establishment of the site compounds will include stripping of the peat

overburden and some subsoil to provide a firm level subgrade, including the temporary storage of

these materials to facilitate subsequent reinstatement, placing of a layer of compacted stone fill

over the surface of the compound, fencing and all associated drainage infrastructure. Toilet facilities

will be provided within the compound and these have the potential to cause contamination of

groundwater and watercourses if the appropriate mitigation measures are not put in place. Similarly,

the refuelling of plant and machinery within the compound also needs to be appropriately

addressed.

The HHIA Report identifies that the construction of the compounds will have a slight temporary

impact on hydrology. Measures will be required to mitigate potential impacts on hydrology. Impacts

on hydrogeology are not considered to be significant.

7.3.1.3 Widening/Upgrading of Existing Access Track

The scope of the project will include the upgrading of c. 2,060m of existing forestry access tracks and

associated drainage infrastructure including widening, strengthening and realignment of the

carriageway, and the provision of cut-off drains, culverts, check dams, etc. as appropriate.

Potential impacts on water and hydrology include:

• Risk to water quality, aquatic life and reduction in channel capacity/blocking of local

water courses should sediment collected from the bare soil/peat exposed by the


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stripping of soils and peat to widen/realign the tracks be carried into them by surface

water run-off.

• Risk of spillage/leakage of oils and fuels from construction machinery and potential

transport of contaminants in the wheels or run-off from dirty vehicles.

• Risk of washout/generation of runoff contaminated with sediments by rainfall falling on

stockpiles of topsoil and other excavated materials during construction and its effect on

the water quality and potential for increased siltation should it discharge to nearby

watercourses.

The HHIA Report identifies that the upgrading of the existing access tracks has the potential to have

a temporary moderate impact on surface water quality and flow in drains and streams if not

undertaken in accordance with best practice. It can result in damage to drains and streams at

crossing points and excessive silt run-off from the extended surface area of the access road.

Measures will be required to mitigate impacts on hydrology. The impact on hydrogeology is

considered to be imperceptible.

7.3.1.4 Construction of New Access Tracks

The scope of the project includes the construction of c.7.7km of new access track, and associated

drainage infrastructure, to facilitate access to the turbine locations, construction of the turbine

foundations and associated crane hardstanding areas, delivery of the turbines and subsequent

maintenance of the Wind Farm during the operational phase of the development.


• Risk to water quality, aquatic life and reduction in channel capacity/blocking of local

water courses should sediment collected from the bare soil/peat exposed by the

stripping of soils and peat to form the tracks be carried into them by surface water run-

off.

• Risk of spillage/leakage of oils and fuels from construction machinery and potential

transport of contaminants in the wheels or run-off from dirty vehicles.

• Risk of washout/generation of runoff contaminated with sediments by rainfall falling on

stockpiles of excavated materials during construction and its effect on the water quality

and potential for increased siltation should it discharge to nearby watercourses.

• Removal/degradation of peat coupled with an introduction of impermeable surfaces

could reduce the infiltration capacity of the catchment leading to an increase in the

surface water runoff rate and associated peak flows in the local watercourses.

• Disruption of natural drainage patterns by access tracks which could form preferential

drainage pathways which may cause areas of erosion, lead to drying out of peat and

result in larger peak flows into local watercourses.


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The HHIA Report identifies that the construction of new access roads has the potential to result in

temporary moderate impacts on surface water quality and flow if not undertaken in accordance with

best practice. It can result in damage to drains and streams at crossing points, and excessive silt run-

off from the developed access road. Measures will be required to mitigate impacts on hydrology.

7.3.1.5 Construction of Turbine Foundations and Crane Hardstandings

The turbines will be supported on large reinforced concrete foundations on competent substratum

below the peat and any weaker subsoils. Hardstanding areas will be constructed adjacent to each of

the turbines to facilitate the off-loading, laydown, assembly and erection of the turbines. The

construction of the crane hardstanding areas will involve excavating down to a competent subgrade,

on the underlying clay/rock and the placement of a layer/layers of compacted stone fill on a

competent subgrade.


• Potential increase in sediment associated with excavations for turbine foundations and

crane hardstanding areas.

• Alteration of natural drainage patterns across areas of turbine foundations and

associated crane hardstanding and potential reduction of infiltration capacity of subsoil

due to removal of peat could increase surface water runoff.

• Dewatering of turbine foundation excavations could lead to discharge of water with high

sediment concentration to water courses and impact on water quality.

• Risk associated with use of concrete in turbine base, particularly if concrete was to enter

a stream or watercourse impacting on water quality of aquatic life.

• Potential increase in surface water runoff following construction of windfarm due to

possible increase in extent of semi-impermeable surfaces leading to siltation or erosion.

Turbines 3, 5 and 7 lie on the border of the Laune and Blackwater catchments on topographically flat

ground. Drainage will divert the water to the Blackwater catchment. The impact of this will be

temporary and slight.

The HHIA Report identifies that the turbine base and hard stand area construction have the potential

to have slight temporary impacts on surface water due to silt run off from excavations and the use of

concrete to construct turbine bases.

The HHIA Report concludes that slight temporary impacts could occur on surface and groundwater

if/where dewatering of hard stand excavations are required. However the elevated nature of the site

and observations during the geotechnical site investigations indicate that groundwater inflows are

unlikely to be significant. Measures will be required to mitigate potential impacts on hydrology.

7.3.1.6 Construction of Meteorological Masts

It is proposed to construct two Meteorological Masts, one located c.100m south west of T12 and the

second located south of T7. They will be supported on reinforced concrete foundations on a


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competent substratum below the peat and any weaker subsoils. The mast base construction has the

potential to have temporary slight level impacts on surface water, due to silt run off from

excavations and the use of concrete to construct foundation areas.

Slight, temporary impacts could occur on surface and groundwater if/where dewatering of

foundation excavations are required. The elevated nature of the site and observations during the

geotechnical site investigations indicate that groundwater inflows are unlikely to be significant.

Measures will be required to mitigate potential impacts on hydrology.

7.3.1.7 Construction of Substations

As outlined in Chapter 2 of this EIS, the scope of the development includes the construction of two

Wind Farm substation compounds, one in the townland of Knocknageeha, on the northern western

side of the L3013 Local Primary County Road, and the other in the townland of Ballynahulla, on the

northern side of the unsurfaced L11128 Local Tertiary Road which passes through the site.

The construction of the compounds will involve the removal of peat overburden and some

underlying subsoil to provide a level competent subgrade for the construction of the compounds.

The medium voltage substation compound at Knocknageeha will cover an area of c.1,565m2 and will

include control building, compound fencing and outdoor switchgear including house transformer.

The larger substation compound in Ballynahulla containing a medium and a high voltage substation

will cover an area of c.6,705m2 and will include control building and outdoor switchgear including

busbars, line bays, grid transformer and associated plinths and bunds. The works will include all

associated drainage infrastructure.


• Increased sediment loading to local water courses as a result of soil-stripping to area of

compound.

• Potential pollution of surface water run-off, groundwater and watercourses from

substances (including oils and fuels) stored within the compound.

• Risk of sewage pollution from temporary toilet facilities.

The HHIA Report identifies that the construction of the substations has the potential to have a slight

impact on surface and groundwater and measures will be required to mitigate the risks.

7.3.1.8 Underground Cable Circuits and Grid Connection

As detailed in Section 2.3 of this EIS, the project will include the construction of the following

underground cable circuits:

Medium voltage underground cable circuit connecting turbines T1 – T7 to the new Wind

Farm substation at Knocknageeha. Approximately, 5.8km of ducted cable trench and

associated jointing bays will be required in the southern section of the Wind Farm along

existing and new Wind Farm track and public roads.


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Medium voltage underground cable circuit connecting turbines T8 – T14 to the new

Wind Farm substation at Ballynahulla. Approximately, 5.3km of ducted cable trench and

associated jointing bays will be required in the northern section of the Wind Farm along

existing and new Wind Farm track and public roads.

Medium voltage underground cable circuit connecting the new Wind Farm Substation at

Knocknageeha to the new Grid Connection Substation Ballynahulla comprising c. 4km of

ducted cable trench and associated jointing bays under the public road.

High voltage underground cable circuit connecting the Grid Connection Substation at

Ballynahulla to Eirgrid’s 110/220kV substation comprising c. 410m of ducted cable

trench and associated jointing bays along the unsurfaced public road.

Some of the cable routes along public roads will cross watercourses at existing

bridges/culverts. All cable trenching will be ducted along the roadway on the bridges,

therefore, no instream works will be required to facilitate cable works.

The HHIA Report identifies that the construction of these cable circuits will have the potential for

slight impacts on hydrology where a cable route crosses the bridge over a drain or stream, and

mitigation measures will be required to minimise potential impacts on surface water flow. No

significant impact is envisaged on groundwater quality as the cable routes will be shallow and will

not extend to bedrock or below the water table.

7.3.1.9 Borrow Pits and Repositories

As identified in Section 2.3 of this EIS, three borrow-pits will be established to provide a local source

of stone fill material for use in the construction of the Wind Farm. Repository areas will be provided

close to each borrow pit to facilitate the temporary stockpiling of any overburden material removed

from the borrow pit and any surplus excavated material from the turbine foundation, access track

and crane hardstanding area construction. These materials will be used for the subsequent re-

instatement of the borrow-pits following completion of the removal of stone for the Works.


Mixing of both groundwater encountered during the excavation of the borrow-pit and

surface water run-off from within and flowing into the borrow-pit with rock fines and

sediment created in the pit which could potentially impact on watercourses or water

supplies in the vicinity if not treated appropriately.

Increase in groundwater recharge in areas of exposed bedrock due to loss of attenuation

capacity provided by overburden removed to facilitate extraction of rock from borrow-

pit.

Potential temporary reduction in base flows to springs and watercourses if water table

level is drawn down during dewatering. This should only be temporary as levels should

stabilise once pumping has ceased.


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The HHIA Report identifies that the borrow pits will have a temporary slight level impact on

hydrology and hydrogeology in the immediate vicinity of the pits. The borrow pits will be excavated

using rock breakers fitted to mechanical excavators. There is the potential for minor leaks or spills of

hydraulic oils or fuel oils from this equipment, which could impact water quality locally in the

bedrock aquifer beneath the borrow pits. However, the impact of the development of the borrow

pits is not considered to be significant at the local or regional scale. Measures will be required to

mitigate potential impacts during construction on surface water and groundwater quality.

7.3.1.10 Summary of the Construction Phase Impacts

The table below summarises the Construction Phase Impacts on Hydrology and Hydrogeology.

Measures will be required to mitigate the impacts and these are outlined in Section 7.4.

Figure 7-3. Construction stage impacts on hydrology and hydrogeology

Activity Duration Importance Magnitude Significance

Tree Felling Temporary Moderate Low Moderate

Construction of new Access Roads Temporary Moderate Low Moderate

Widening/Upgrading of Existing Access

Tracks

Temporary Moderate Low Moderate

Construction of Turbine Bases and

Hard Standing Areas

Temporary Low Low Slight

Construction of Meteorological Masts Temporary Low Low Slight

Borrow Pits and Repositories Temporary Low Low Slight

New Drains Temporary Moderate Low Moderate

Upgrading of Existing Drains and

Stream Crossings

Temporary Moderate Low Moderate

Construction of Sub Stations Temporary Low Negligible Slight

Underground Cable Routes and Grid

Connection

Temporary Low Negligible Slight

Construction Contractors Compound Temporary Low Negligible Slight

7.3.2 Operational Stage Impacts

Operational activities will comprise visits by company staff to maintain and/or repair equipment in

the turbines, support systems in the substation buildings and maintenance of the roads and the

surface water drainage system.

The substation buildings will be surrounded by palisade fencing. The Control Building will be

unmanned, but will contain toilet facilities within an associated holding tank for maintenance staff

and the transformers in the substations will contain cooling oils.

There is the potential for localised impact on hydrology and hydrogeology in the event that toilet

facilities are not maintained, or the transformer oils were to leak to ground causing soil and possibly

groundwater contamination. Given the limited volume of wastewater likely to be generated (c1-

2m3/year) the impact would be temporary and of negligible significance.


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Road maintenance work could result in localised generation of silt which could run off to drains and

water courses. The impacts are considered to be temporary i.e. over the period of maintenance,

and of slight impact on hydrology with negligible impacts on hydrogeology.

Maintenance work on drains, water courses and stream crossings could result in impacts on surface

water quality. The impacts are considered to be temporary i.e. over the period of maintenance, and

of slight impact on hydrology with negligible impacts on hydrogeology.

The cumulative impacts of other activities within the catchment during the operational phase are

considered to be temporary moderate impact on hydrology and negligible impact on hydrogeology.

Measures are required to mitigate the associated impacts and these are described in Section 7.4.

7.3.2.1 Decommissioning Stage Impacts

Impacts during decommissioning will be limited to the dismantling and removal of the turbines from

the site. It is not proposed to remove the turbine bases or the substations.

By the time decommissioning takes place the borrow pit areas will be fully reinstated, and all

previously soil stripped areas will have been revegetated. The surface water drainage will have

stabilised, with sediment run-off from the site similar to undeveloped areas. Decommissioning

impacts will be limited to the movement of vehicles and equipment to remove the turbines.

The impact of the decommissioning works will be temporary, and of negligible significance on the

Hydrology and Hydrogeology of the site.

7.3.3 Cumulative Impact

Activities within this part of the Wind Farm catchment are dominated by forestry, agriculture and

turf cutting. Turbines T-1 to T-7 are in areas associated with past and recent cut away bog with small

areas of wet grassland to the north of T-5 and T-6 and to the south of T-7. Turbines T-8, 9 and 13 are

also located in cut away bog. While turbines T-11 and 12 are in wet grassland. There is a portion of

improved agricultural lands to the southeast of T-14.

Cut away bogs that are being actively cut have the potential to impact on surface water quality if

sediment run-off is not controlled.

Forestry may impact on the surface water quality during planting, application of forestry fertiliser

and tree felling activities.

Agricultural activities can result in runoff/emissions of silt, nutrients and pesticides to receiving

watercourses, which can reduce water quality.

However, the ecological status of the streams associated with the site are classified as Good

indicating that forestry, peat cutting and agricultural activities are not having an overly negative

effect on water quality within this part of the catchment.

In the absence of mitigation and in the event that the above activities were having adverse effects

on water quality at the same time the wind farm was being constructed, cumulative impacts on

water quality could potentially be considered to be of moderate significance. However, a Planning


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Stage Surface Water Management Plan (see Appendix 7B and Drawings 17924 5016-5024), which

will be implemented during the construction phase, has been developed for the wind farm that

would mitigate such impacts.

7.4 MITIGATION

7.4.1 Construction Stage Mitigation Measures

Sediment, including any soils, mud, silt, sand, etc., arising from the erosion of exposed soils and

construction materials used to construct the access tracks, substation and construction compounds,

crane hardstanding areas, etc. by surface water runoff, is the single main source of pollution with the

potential to have an impact on water quality in the watercourses downstream of the site. The

adoption of appropriately robust erosion and sediment controls before, during and after

construction will be the essential key to ensuring the prevention of sediment laden runoff to these

river catchments.

The project will commit to adopting stringent best practices regarding erosion and sediment control

on the site and to complying with all relevant guidance contained in the following documents in

relation to the planning, development and operation of the Wind Farm:

Forestry and Water Quality Guidelines – Forest Service (July 2000).

Forestry and Freshwater Pearl Mussel Requirements – Site Assessment and Mitigation

Measures – Forest Service (2009).

Forest Operations and Water Quality Guidelines – Coillte (Updated September 2009).

Control of water pollution from linear construction projects. A Technical Guidance. A

CIRIA publication, UK. Murnane, E., Heap, A. and A. Swain, 2006.

As detailed in Section 2.4 of this EIS, prior to commencement of construction of the proposed

Silverbirch Wind Farm development, a Construction and Environmental Management Plan (CEMP)

will be prepared for the project. The CEMP is intended as a guidance document for the construction

of the Wind Farm, and will identify for the Contractor the key planning and environmental

constraints and associated mitigation measures which need to be adhered to in order to ensure that

the project can be delivered in a manner which complies with the relevant statutory obligations and

environmental best practice.

In the context of Storm Water Management, Sediment and Erosion Control and Water Quality,

compliance with the intent of the above documents will be a key objective of the CEMP, and is

reflected in the guidance and mitigation measures set out below and in the Silverbirch Wind Farm

Surface Water Management Plan. The Planning Stage Surface Water Management Plan has been

prepared for this project and will be incorporated in the CEMP and will be implemented as stated

unless otherwise agreed in writing with Kerry County Council (see Appendix 7B and Drawings 17924-

5016 to 5024). It is important to clearly distinguish between erosion control and sediment control:


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Erosion control is intended to prevent surface water runoff flowing across exposed

ground and becoming polluted with sediments.

Sediment control is designed to slow run-off to allow any suspended solids to settle out

in situ.

The key Principles of Erosion and Sediment Control identified in CIRIA Report C648 (Control of Water

Pollution from Linear Construction Projects) and reflected in the Silverbirch Wind Farm Surface

Water Management Plan are as follows:

1. Erosion control (preventing runoff) is much more effective than sediment control in

preventing water pollution. Erosion control is less subject to failure from high rainfall,

requires less maintenance and is also less costly.

2. Plan erosion and sediment control early in the project and incorporate into the works

programme.

3. Install drainage and runoff controls BEFORE starting site clearance and earthworks.

4. Minimise the area of exposed ground.

5. Prevent runoff entering the site from adjacent ground, as this creates additional polluted

water.

6. Provide appropriate control and containment measures on site.

7. Monitor and maintain erosion and sediment controls throughout the project.

8. Establish vegetation as soon as practical on all areas where soil has been exposed.

The mitigation measures presented in the following sections, including sediment and erosion control

measures which are reflected in the project Surface Water Management Plan, have been identified

for each element of the works.

7.4.1.1 Forestry Felling

Tree feeling will be undertaken in accordance with best practice guidance including;

• Forestry and Water Quality Guidelines - Forest Service (2000).

• Forest Operations and Water Protection Guidelines - Coillte (2009).

• Methodology for Clear Felling Harvesting Operations - Coillte (2009).

• Forestry and Freshwater Pearl Mussel Requirements –Site Assessment and Mitigation

Measures - Forest Service (2009).


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Where feasible, a 50m buffer zone will be maintained between the felling area and all watercourses.

With the exception of access roads to T9, T10, existing road upgrades and an existing stream

crossing, all the proposed tree felling areas are outside the buffer zones, therefore runoff from the

tree felling areas will be attenuated prior to reaching surface water courses. Where tree felling is

required in the vicinity of streams, the following mitigation measures will be implemented:

• Works will not take place in periods of sustained high rainfall, in order to minimise

entrainment of sediment to drains and streams.

• Low ground pressure plant will be utilised for felling to minimise ground disturbance;

• Monitoring and maintenance of roads, drains and culverts will be undertaken during the

course of felling operations.

• Existing forestry drains will be blocked upstream of the confluence with any surface

water streams and temporary silt traps will be deployed. No direct discharge from these

drains will occur during tree felling activities.

• In steeper areas where there is a potential for soil erosion brash mats will be used along

off-road routes. Off-road tracking will be suspended during periods of high rainfall.

• Felled timber will be stacked in dry areas, and outside of the buffer zones.

• Refuelling or maintenance of plant and machinery will not be permitted within 100m of

a watercourse. Spill kits will be provided at the refuelling areas. All of the felling

machinery operating in or near these watercourses will be systematically checked in

order to avoid leaks of oils, hydraulic fluids and fuels.

7.4.1.2 Site Establishment and Construction Compounds

The following mitigation measures will be implemented during site establishment and the

preparation of construction compounds:

• Installation of interception ditches upslope of Construction Compounds to intercept

existing overland flows (clean water) and convey it downslope in order to limit extent of

surface water coming into contact with the works. These ditches will be installed prior to

construction of the construction compound(s) and the water collected will be discharged

via a level spreader downslope of the works.

• Installation of perimeter drains to collect surface water runoff from the Construction

Compound.

• Installation of check dams at regular intervals in perimeter drains.

• Installation of silt traps at outlets from perimeter drains.


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The following mitigation measures will be implemented during the course of the construction works:

• All construction materials with the potential to impact on soil or waters (concrete

materials, fuel and lubricating oils) will be stored in appropriately bunded areas in the

contractors compound.

• Re-fuelling will take place at a specific designated re-fuelling area in the contractor’s

compound. This re-fuelling area will be appropriately bunded.

• Maintenance of construction vehicles or plant will only be permitted at the contractor’s

construction compound.

7.4.1.3 Upgrading of Existing Access Track

The following mitigation measures will be implemented during the upgrading of existing access

tracks:

• Installation of check dams in existing roadside drains.

• Provision of new roadside drains where not currently provided or where required to

facilitate widening/realignment of existing track.

• Installation of silt traps on outlets from roadside drains and, where appropriate, on

existing drainage channels receiving the discharge from roadside drains.

• Blocking of existing drainage channels, where appropriate (e.g. where they discharge

directly to existing watercourses and there is a risk of sediment discharge as a

consequence of same).

• Installation of interception ditches, where appropriate, upslope of existing access tracks

to intercept existing overland flows (clean water) and convey it downslope in order to

limit extent of surface water coming into contact with the works.

• Provision of silt fences at any existing watercourse crossings extending min. 10m either

side of crossing and discharging via appropriately designed and positioned silt traps.

7.4.1.4 Construction of New Access Track

The following mitigation measures will be implemented during the construction of new access

tracks:

• Installation of interception ditches upslope of new access tracks to intercept existing

overland flows (clean water) and convey it downslope in order to limit extent of surface

water coming into contact with the works. These ditches will be installed prior to

construction of each section of the new access tracks and the water collected will be

discharged via a level spreader downslope of the new access track.


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• Installation of check dams at regular intervals in roadside drains.

• Installation of silt traps at outlets from roadside drains.

• Installation of level spreader downstream of silt traps to facilitate discharge of treated

water from roadside drains.

• Installation of any interception drains required across access tracks to prevent surface

water flowing along carriageway, particularly on steeper sections of track.

7.4.1.5 Construction of Turbine Foundations and Crane Hardstandings

The following mitigation measures will be implemented during the construction of the turbine

foundations and associated crane hardstanding areas:

• Installation of interception ditches upslope of crane hardstanding area/turbine

foundation to intercept existing overland flows (clean water) and convey it downslope in

order to limit extent of surface water coming into contact with the works. These drains

will be installed prior to construction of each crane hardstanding area/turbine

foundation and the water collected will be discharged via a level spreader downslope of

the works.

• Installation of perimeter drains to collect surface water runoff from the crane

hardstanding area/turbine foundation.




water from perimeter drains.

• Installation of temporary sediment basin to facilitate dewatering of turbine foundation

excavation including associated silt traps and level spreader for discharge of treated

water.

7.4.1.6 Construction of Sub-station Compounds

The following mitigation measures will be implemented during the construction of the substation

compounds, control buildings and installation of associated electrical infrastructure:

• Installation of interception ditches upslope of Substation Compound to intercept existing

overland flows (clean water) and convey it downslope in order to limit extent of surface


construction of the substation compound and the water collected will be discharged via

a level spreader downslope of the works.


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• Installation of perimeter drains to collect surface water runoff from the Substation

Compound.




water from perimeter drains.

7.4.1.7 Underground Cable Circuits

The following mitigation measures will be implemented for the construction of cable trenches within

the Wind Farm:

• Cable runs will be installed alongside existing/proposed access tracks where appropriate

in order to minimise ground disturbance and subsequent wash-out of mud and silt.

• Where cable routes cross over drains or streams appropriate sediment and erosion

control measures will be installed.

The following mitigation measures will be implemented for the construction of cable trenches and

associated jointing bays along the public road:

• All material excavated to form the trenches and jointing bays will be immediately

removed to a licensed waste facility and will not be stockpiled close to the works in

order to prevent potential silt laden run-off to existing roadside drains and

watercourses.

• Where cable routes cross over drains or streams appropriate sediment and erosion

control measures will be installed.

7.4.1.8 Borrrow Pits and Repositories

The following mitigation measures will be implemented during the establishment and operation of

borrow pits and repositories during the construction of the Wind Farm:

• Installation of interception ditches upslope of borrow-pit to intercept existing overland

flows (clean water) and convey it downslope of same in order to limit extent of surface


excavation of the borrow-pit and the water collected will be discharged via a level

spreader downslope of the works.

• Installation of collection drains within proposed borrow-pit to collect potentially silt

laden run-off and discharge of same via sump to settlement basins for treatment.


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• Installation of interception drains at access point to borrow-pit to intercept potentially

silt laden run-off and discharge of same to settlement basins for treatment.

• Installation of oil interceptor on discharge from sediment basins.

• Installation of level spreader to facilitate dispersal of treated water.

7.4.2 Operational Stage Mitigation Measures

The following mitigation measures will be implemented during the operational phase of the Wind

Farm:

• Substation transformers will be located within impermeable concrete bunds with a

capacity to retain 110% of the capacity of the oil in the transformer in the event of a

leak. Drainage from the bunds will pass through an oil interceptor.

• Wastewater from toilets in the substation will be treated using a proprietary treatment

system and the treated effluent discharged to an underground tank which will be

emptied as required by a licensed waste contractor. The tank will be appropriately

vented and alarmed.

• Access tracks and hardstanding areas will be maintained to ensure they have an

adequate cross-camber and to prevent rutting of the surface in order to prevent erosion

and silt run-off into trackside drains and watercourses and to prevent formation of

preferential drainage channels.

• Trackside drains, drains and silt traps will be regularly maintained.

• A documented emergency procedure will be in place to cope with any accidental

spillages.

• Turbine transformers will be fully bunded and the maintenance contract for the turbines

will require all waste materials including waste oils and lubricants and their packaging to

be collected and transported off site for disposal or reprocessing by a licensed waste

contractor.

7.4.3 Decommissioning Phase Mitigation Measures

The following mitigation measures would be implemented during the decommissioning phase of the

project:

• A works compound will be established for the storage of equipment and fuel and the

same mitigation measures adopted as for the construction stage compound, as

appropriate.

• Only the concrete plinths/foundation rings will be removed with the hardstanding areas

and tracks left in-situ and reinstated with a layer of peat which will be revegetated.


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Landscaping of this cover will ensure that drainage paths are unaltered and remain

similar to previous conditions.

• The underground cable network will be cut-off at ground level and left in-situ, thereby

avoiding excavation works and any potential hydrological effects associated with same.

7.4.4 Monitoring

The CEMP will be finalised prior to commencement of siteworks. The CEMP will include detailed

Method Statements and a Construction Stage Surface Water Management Plan for the Works.

Construction Stage Geotechnical Investigations and Risk Assessments will include provision for

monitoring of the works to prevent any significant impacts on water quality. These will include:

• Supervision of the Works by appropriately qualified and experienced personnel.

• Regular inspections of equipment and lubricant fuel stores to ensure the risk of potential

contamination associated with a spillage is minimised.

• Assignment of a unique reference number to each silt control feature on site so that an

onsite quality control system can be implemented for the monitoring and maintenance

of each trap.

• Baseline, construction phase and post construction phase water quality monitoring.

• Water Quality Monitoring points, schedule and parameters to be tested.

The following monitoring measures will be put in place during the operational phase of the

development to prevent impacts on water quality:

• Access roads and crane hardstanding areas will be inspected bi-annually to ensure they

have an adequate cross-camber and to prevent rutting in order to prevent erosion and

silt run-off into trackside drains and watercourses and to prevent formation of

preferential drainage channels.

• Trackside drains, drains and silt traps will be regularly maintained and will be inspected

bi-annually to ensure that they are operating effectively.

7.5 RESIDUAL IMPACTS

It is concluded that the construction, operation and subsequent decommissioning of Silverbirch

Wind Farm will not have a significant impact on the hydrology and hydrogeology of the receiving

environment. Appropriate mitigation measures have been designed to avoid or minimise any impact

on water quality.


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7.6 CONCLUSION

The development has, in absence of mitigation measures, the potential to cause adverse impacts on

the hydrology and hydrogeology of the receiving environment. However, the proposed design and

method of construction and operation as well as the Surface Water Management Plan incorporate

measures that effectively mitigate those risks. Provided all mitigation is appropriately implemented,

the residual impact of Silverbirch Wind Farm is not considered to be significant.

Documents

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