Sgurr Energy Ltd Linfairn Wind Farm Appendix 9.4 ... Dependent Terrestrial Ecosystems Risk...

This Document is of UK Origin

Sgurr Energy Ltd

Linfairn Wind Farm

Appendix 9.4

Groundwater Dependent Terrestrial Ecosystems Risk

Assessment

September 2013

This Document is of UK Origin

EnviroCentre Document No. 5631

EnviroCentre Project No. 161766j

Status Final

Project Manager Hannah Barker

Project Reviewer Lucila Lantschner

Date of Issue September 2013

Filename linfairn_gwdte_final_reva.docx

EnviroCentre

Craighall Business Park

Eagle Street

Glasgow

G4 9XA

t 0141 341 5040

f 0141 341 5045

w www.envirocentre.co.uk

e [email protected]

Offices

Glasgow

Banchory

This document has been prepared for the Client named on this front cover. EnviroCentre accept no liability or responsibility for any

use that is made of this document other than by the Client for the purpose of the original commission for which it has been prepared.

Sgurr Energy September 2013

Linfairn Wind Farm: GWDTE Risk Assessment

i

Linfairn Wind Farm

Groundwater Dependent Terrestrial Ecosystem Risk Assessment

Table of Contents

1. Introduction ................................................................................................................................. 2

1.1 Terms of Reference ............................................................................................................................................. 2 1.2 The Site ................................................................................................................................................................ 2 1.3 Methodology ....................................................................................................................................................... 2

2. Qualitative Assessment ............................................................................................................... 3

2.1 Site Hydrogeology ............................................................................................................................................... 3 2.2 GWDTE Identification ......................................................................................................................................... 3 2.3 Nearby Site Infrastructure .................................................................................................................................. 5 2.4 Qualitative Risk Assessment ............................................................................................................................... 5

3. Mitigation Measures ................................................................................................................. 23

Figures (Volume 3 of ES):

Figure 9.13a GWDTEs and Flow Directions (1 of 2)

Figure 9.13b GWDTEs and Flow Directions (2 of 2)

List of Tables

Table 2.1: GWDTEs at the site ................................................................................................................................................. 4

Table 2.2: GWDTE sensitivity ................................................................................................................................................... 4

Table 2.3: Risk Assessment Matrix .......................................................................................................................................... 6



2

1. INTRODUCTION

1.1 Terms of Reference

EnviroCentre Ltd has been commissioned by Sgurr Energy to carry out a Water and Soils assessment for the proposed

Linfairn Wind Farm, located near to Straiton, South Ayrshire. This report forms a Technical Appendix to Chapter 8

(Water Environment & Soils) of the Environmental Statement (ES) for Linfairn Wind Farm and should be read with

reference to this chapter.

The National Vegetation Classification (NVC) survey undertaken for the site identified areas of Groundwater

Dependent Terrestrial Ecosystems (GWDTEs) in the buffer zones defined by the current SEPA guidance1 (referred to as

the SEPA guidance within this report). This report details the qualitative assessment which has been undertaken to

identify any risks of the development on these GWDTEs and outlines suitable mitigation measures.

1.2 The Site

The proposed wind farm development consists of 25 WTGs and associated hardstandings, access tracks, two site

compounds and a sub-station building. There are no borrow pits proposed at the site. Access to the proposed site will

be from minor road situated to the north of the site. The site includes a variety of lowland and upland habitats ranging

from blanket bog to improved pasture. The majority of the site is currently used for grazing, with commercial forest

plantation present in the north-eastern part of the site.

1.3 Methodology

The following methodology was used for the GWDTE assessment:

• Identification of GWDTE on the site;

• Identification of site infrastructure located within buffer zones of GWDTE;

• Analysis of relevant hydrogeological conditions for each GWDTE;

• Qualitative assessment of the risks to each GWDTE from site infrastructure;

• Identification of mitigation measures to minimise any risks to GWDTEs; and

• Report summarising the findings of the assessment.

1 SEPA. 2012. LUPS Guidance Note 4: Planning guidance on windfarm developments. Version 6.



3

2. QUALITATIVE ASSESSMENT

2.1 Site Hydrogeology

The site hydrogeological baseline conditions are described in the Water & Soils ES chapter and can be summarised as

follows:

• The site is underlain by both sedimentary (sandstone, siltstone, mudstone) and igneous rocks (volcanic

formations), with the majority of the southern part of the site underlain by igneous rock.

• Where sedimentary rocks are present, the bedrock aquifer is classified as having moderate productivity with

groundwater movement via inter-granular and fracture flow.

• Where igneous rocks are present, the bedrock aquifer is classified as having low productivity with

groundwater movement occurring via fracture flow.

• A number of faults are located within the site area.

• Drift deposits are absent across much of the higher ground, while Devensian till is present at lower

elevations. Where till is present the drift aquifer is classified as having a low productivity.

• Peat deposits are present in localised pockets at the site, in valley bottoms in the northern part of the site

and flatter upland plateau areas in the south of the site. Flows within peat deposits are typically limited to

the upper layer (acrotelm, typically <0.5m), with very limited groundwater flow expected in deeper peat

(catotelm) other than where subsurface peat pipes are present.

• Where peat deposits are absent, both freely draining and poorly draining soils are present.

2.2 GWDTE Identification

The GWDTEs located within the site were identified on the basis of the NVC survey (Chapter 7 of the ES). For the

access route between the northern and southern part of the site the GWDTEs have been identified on the basis of the

Phase 1 habitat survey as an NVC survey has not been carried out; all areas of marshy grassland were considered as

potential GWDTEs. Mosaic habitats are common across the site, and any mosaics containing GWDTE NVC habitats,

based on Table 2 in Appendix 2 of the SEPA guidance, and classified as marshy grassland, valley mire, wet dwarf shrub

heath, wet modified bog or a flush habitat were considered as GWDTE’s in the assessment. The distribution of

GWDTEs within the site is shown in Figure 9.13.

Table 2.1 lists the NVC communities identified as GWDTEs at the site, both where they occur as distinct communities

and within mosaics. Their groundwater dependency, based on the UKTAG NVC tables2 is also provided. The supporting

hydrogeological conditions for each NVC community are discussed below, based on habitat information from the NVC

volumes3.

The M6 community is an acid flush habitat which is found in low nutrient and base-poor conditions. It is dependent on

the flow of water/ flushing, which can be from upslope springs or seepage lines, or from the concentration of surface

water draining to streams or tracks. It is therefore usually present as a linear feature, as at this site, or adjacent to

watercourses.

M10 is a basic flush habitat which is dependent on groundwater springs or the emergence of groundwater providing

base-rich waters from bedrock or superficial deposits. As such this habitat is highly dependent on groundwater and is

typically present as a linear feature associated with spring heads and spring lines.

2 UKTAG list of NVC communities 210513, access at

http://www.wfduk.org/sites/default/files/Media/Characterisation%20of%20the%20water%20environment/UKTAG%20list%20of%20NVC%20commu

nities_210513.pdf

3 UK Joint Nature Conservation Committee, 1998. British Plant Communities, edited by J.S. Rodwell.



4

M15, a wet heath, is classified in Table 2.1 as being moderately groundwater dependent. This habitat is generally

associated with wet but not waterlogged conditions in areas of better drained peat, thin peat or sloping ground,

where the water movement is of through-flow in the near-surface soil layers rather than groundwater emergence.

This is reflected in the distribution of the habitat across the site, which is strongly influenced by the localised

topography. Acidic and oligotrophic conditions are associated with the peat substrates upon which this habitat is

typically found.

M23, a marshy grassland, is widespread across the site and is the dominant GWDTE community, accounting for 29% of

the area within the site boundary; the other GWDTEs combined account for 11% of the area within the site boundary.

The distribution of this habitat is influenced by the site topography, and it is usually found in poorly drained valleys or

hillslopes and adjacent to flushes and mires. This habitat, similar to M15, is dependent on shallow through-flow from

surrounding slopes and is influenced by the level of drainage within localised valleys. This community is maintained by

grazing.

Modified bog, M25, is dependent on wet conditions and is particularly prevalent in the west of Scotland due to the

high annual rainfall totals. This habitat prefers wet but not waterlogged conditions and is therefore associated with

areas where bog has been modified through drainage and/ or grazing. It is generally found on gently sloping ground

and can extend onto ombrogenous (i.e. rainwater fed) bogs. The groundwater-dependency of this habitat is therefore

limited.

Table 2.1: GWDTEs at the site

Phase 1 habitat NVC Community1

Groundwater Dependency

(based on UKTAG tables)

Mire – acid flush M6 Carex echinata-Sphagnum recurvum/auriculatum mire High

Mire – basic flush M10 Carex dioica-Pinguicula vulgaris mire High

Wet dwarf shrub

heath

M15 Scirpus cespitosum-Erica tetralix wet heath

Moderate

Marshy grassland M23 Juncus effusus/acutiflorus-Galium palustre rush-pasture Moderate

Wet modified

bog/ valley mire

M25 Molinia caerulea-Potentilla erecta mire Low

1 Descriptions of NVC communities provided in Chapter 7 of the ES.

The sensitivity, or value, of the GWDTEs has been determined on the basis of their rarity, their condition at this site

and their groundwater dependency, as detailed in Table 2.2. The M15, M23 and M25 habitats are common and

widespread through Scotland, particularly M23 and M25, and all the GWDTEs at the site has been influenced to a

greater or lesser extent by grazing, poaching and drainage.

Table 2.2: GWDTE sensitivity

NVC Community Rarity Condition at site Sensitivity

M6 Common in Scotland, usually present in small, linear

stands

Below average –

grazing Low

M10 Less common, but not rare, usually present in small,

linear stands Average Medium

M15 Common in Scotland Average Low

M23 Common and widespread in Scotland Average Low

M25 Common in Scotland particularly in the west Average Low



5

2.3 Nearby Site Infrastructure

The construction of turbines, tracks and other on-site infrastructure has the potential to disrupt flow of water to

GWDTEs and there is a risk of pollution of groundwater from contaminated discharges during construction or

decommissioning. Excavations for turbines foundations also have the potential to change the quantity of flow

supplying GWDTEs due to dewatering.

The majority of the proposed infrastructure is within 100m of GWDTEs. Given the widespread nature of GWDTEs at

the site, particularly in the southern part of the site, it has not been possible for the infrastructure to avoid these

habitats. The remainder of this report therefore outlines risks posed by the infrastructure on these receptors and

details on how GWDTEs will be protected.

2.4 Qualitative Risk Assessment

The distribution of GWDTEs at the site is predominantly controlled by the influence of topography on shallow through-

flow. The dominant flow direction is therefore assumed to be topographically controlled, and has been mapped in

Figure 9.13 to enable the key risks from the infrastructure to be identified.

Table 2.3 provides a qualitative assessment of the risks from each infrastructure element to the GWDTEs at the site,

based on the following assumptions:

• Turbine foundations situated up-gradient of a GWDTE could disrupt shallow groundwater flow during

construction through dewatering and alter the flow paths;

• Turbine foundations situated down-gradient from a GWDTE could under certain conditions affect the

GWDTE during construction due to dewatering;

• Tracks and other infrastructure up-gradient could disrupt groundwater flow/ alter flow paths if oriented

perpendicular to the dominant shallow groundwater flow path, however disruption will be minimal if the

track is oriented parallel to these flow paths.

• Tracks and other infrastructure down-gradient from a GWDTE could alter flow paths and lead to localised

ponding if oriented perpendicular to the dominant shallow groundwater flow path, however disruption will

be minimal if the track is oriented parallel to the flow path.

The potential impact magnitude assigned in Table 2.3 is based on the criteria in Table 3 in Chapter 9 of the ES. The risk

is only considered to be high where a total loss or major damage of the receptor is expected. The majority of the

GWDTEs at the site are influenced by rainwater supply, through-flow and the level to which drainage is impeded, and

as such major damage of this receptor is unlikely in most cases. The direct loss of habitat is considered with Chapter 7

of the ES, however it is noted in Table 2.3 for information. Mitigation measures are summarised in this table and are

detailed further in section 3.



6

Table 2.3: Risk Assessment Matrix

Infrastructure

element

GWDTE

sensitivity

GWDTE description Description of Effect on GWDTE Direct

loss of

GWDTE?

Pre-

mitigation

Risk

Key mitigation Residual

Risk

WTG1

M23 low,

M15 low

Nearest GWDTE is

200m east – mosaic

consisting of 25%

GWDTE (M23/ M15)

GWDTE is 200m from WTG and is

characterised by small hollows/

valleys i.e. the catchment area of the

through-flow component is very

localised in extent. Turbine therefore

unlikely to affect flow contribution to

GWDTE.

N Negligible • Time excavations open minimised and excavations

reinstated as soon as practicable.

• Temporary cut-off drains to prevent water entering

excavation.

• Pollution prevention measures.

Negligible

Track WTG1 –

WTG2

(556m)

M23 low,

M15 low

134m of track located

within GWDTE (M15/

M23)

Track located within GWDTE

orientated perpendicular to dominant

flow direction, potentially disrupting/

altering flow paths and affecting

GWDTE up-slope and downslope.

Y Medium • Tracks constructed with a suitable camber from

permeable material of suitable chemistry.

• Cross-drains installed as part of track construction to

preserve existing flow paths.


Low

WTG2 M15 low M15 habitat at and

upslope of turbine.

Moderately sloping ground upslope of

turbine. Localised risk to GWDTE

upslope from dewatering at turbine

foundations.

This would affect a small proportion

of flow contribution to the wider

GWDTE.

Y Localised • Time excavations open minimised.


excavation.

• Drainage/ pumping from excavations to be minimised

through appropriate design.

• Water pumped from excavation discharged in

proximity to excavation following treatment.

• Reinstatement should occur as soon as practicable,

ensure suitable hydrological conditions and avoid

permanent draining.


Low

Track WTG2 –

WTG3 (416m)

and WTG3

M23 low,

M15 low

M25 low

Majority of track passes

through GWDTE (M23/

M25/ M15)

Track generally oriented

perpendicular to dominant flow

direction on moderately sloping

ground, potentially disrupting/


GWDTE up-slope and downslope.






Low



7

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG3 M23 low,

M15 low

M25 low

Located within GWDTE

(M23/ M25/ M15)

Potential effect on GWDTE

downslope from disruption of flow

paths, and upslope and downslope

due to dewatering at turbine

foundations.



GWDTE.

Y Low • Time excavations open minimised.


excavation.







permanent draining.


Low

Track WTG3 –

WTG4

including spur

(~1km)

M23 low

M25 low

650m track through/

up-gradient of GWDTE

(M23/ M25)



direction on moderate/ low gradient

slopes, potentially disrupting/ altering

flow paths and affecting GWDTE up-

slope and downslope.






Low

WTG4 M23 low

M25 low


(M23/ M25)



paths, and upslope and downslope


foundations.



GWDTE.



excavation.







permanent draining.


Low



8

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

Track WTG5 –

WTG6 (795m)

M23 low,

M15low,

M25 low

Majority of track passes

through commercial

forestry. GWDTE (M23/

M25/ M15) located

within fire tracks. Small

lengths of track located

up-gradient/ within

GWDTE (~150m)



direction on moderate/ low gradient



slope and downslope. GWDTEs

present with valleys/ minor

watercourses and will in some areas

receive flow from corresponding

surface water catchments.






Low

WTG5 and

WTG6

M23 low,

M15 low,

M25 low

Located in proximity to

GWDTEs (M23/ M25/

M15 in fire tracks)


downslope due to dewatering at

turbine foundations and from

disruption of flow paths.



GWDTE.



excavation.







permanent draining.


Low



9

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

Access into

site

(1580m)

M23 low,

M10

medium

642m track through/

up-gradient of GWDTEs

(M23/ M10). GWDTE

areas are generally

associated with

tributaries of the Cawin

Burn, with some

spring-fed habitats

down-gradient of the

track.



direction on moderate/ high gradient



slope and downslope, including spring

fed habitats.

Potential disruption of flows at

watercourse crossings.

Y Medium • Micro-siting away from more sensitive GWDTE

communities (M10) will be carried out where

possible.

• Tracks constructed with a suitable camber from




• Particular care will be taken to ensure that flow paths

at flushes/ spring lines are maintained through the

track.

• Watercourse crossing will be designed to ensure that

flows are not restricted.


Low

Access

between

north and

south of site

(2586m)

Marshy

grassland,

low

Approx 408m track

through/ up-gradient

of GWDTE (marshy

grassland)

Track generally perpendicular to

dominant flow direction potentially

disrupting/ altering flow paths and

affecting GWDTE upslope and

downslope. Potential effects greater

where slopes steeper (e.g. Cawin Hill)

compared to flatter gradients through

Dalmorton landholding.










Low



10

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

Access to

WTG7 (970m)

M23 low, M6

low, M10

medium

322m of track through

GWDTE (M23/ M10,

localised M6)

Majority of track runs parallel to the

dominant flow direction on moderate

gradient slopes. Track may act as a

preferential flow path but will have a

limited effect on proportion of flow to

the GWDTE.


watercourse crossing.

Y Low • Micro-siting away from more sensitive GWDTE

communities (M10 and M6) will be carried out where

possible.




ensure that track does not act as preferential flow

path.




Negligible

WTG7 M23 low Located within GWDTE

(M23)



paths, on lower gradient slopes.

Potential effect on GWDTE upslope

and downslope due to dewatering at

turbine foundations.



GWDTE.



excavation.







permanent draining.


Low

WTG7 to

WTG8 (355m)

M23 low,

M10

medium

105m track located

within GWDTE

(M23/M10)

Track oriented parallel to dominant

flow direction. Track may act as a

preferential flow path but will have

limited effect on proportion of flow to

GWDTE.



possible.





path.


Low



11

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG8 M23 low,

M10

medium


(M23/ M10)



paths.




Turbine and crane pad located across

a significant part of the GWDTE and

could therefore have a greater effect

on flow contribution.



possible.

• Time excavations open minimised.


excavation.







permanent draining.


Low

WTG8 to

WTG9

M23 low,

M10

medium, M6

low

210m track located

within GWDTE (M23/

M10, localised area

M6)





downslope.





possible.





path.




Low



12

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG9 M23 low,

M10

medium


(M23/ M10)



paths.




Turbine and crane pad located across

a significant part of the GWDTE and

could therefore have a greater effect

on flow contribution.



possible.



excavation.







permanent draining.


Low

WTG9 to

WTG10

(380m)

M23 low 190m track within/ up-

gradient GWDTE (M23)





downslope.










Low


(M23)



paths and dewatering at turbine

foundations.



GWDTE.



excavation.







permanent draining.


Low



13

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG10 to

WTG11

(390m)



Track perpendicular to dominant flow

direction potentially disrupting/


GWDTE upslope and downslope.






Low


(M23)



paths.






GWDTE.



excavation.







permanent draining.


Low

WTG11 –

WTG12

(376m)

M23 low 376m track within

GWDTE (M23)

Track generally oriented parallel to

dominant flow direction. Track may

act as a preferential flow path but will

have limited influence on proportion

of flow to GWDTE.



Y Low • Tracks constructed with a suitable camber from



ensure track does not act as preferential flow path.




Low



14

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk


(M23)



paths.






GWDTE.



excavation.







permanent draining.


Low

Track WTG10

– WTG18

(640m)




flow direction, and low gradient

which will limit movement of

through-flow.






Low

WTG18 M23 low Located adjacent to

GWDTE (M23)

Turbine on flat/ low gradient slope.

Potential effect on GWDTE from

dewatering. ,.



GWDTE.

N Low • Time excavations open minimised.


excavation.







permanent draining.


Negligible

WTG18 -

WTG23

(724m)

M23 low

M25 low

450m track within/ up-

gradient of mosaic

habitat including

GWDTE (M23/ M25)










Low



15

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG23 M23 low,

M25 low, M6

low

Located on localised

small hill on non-

GWDTE. GWDTE within

100m (M23/ M25/ M6)

Potential effect on surrounding

GWDTE due to dewatering at turbine

foundation.

Located at a local high point and

therefore would affect a small

proportion of flow contribution to the

wider GWDTEs.

N Low • Micro-siting away from more sensitive GWDTE

communities (M6) will be carried out where possible.



excavation.







permanent draining.


Low

WTG23 –

WTG22

(322m)



Contour data and aerial photography

suggest track runs along broad ridge,

therefore having minimal influence on

flow paths. This also suggests M23 at

this area is unlikely to be dependent

on groundwater/ through-flow.






Low

WTG22 M23 low Located within mosaic

of 50% GWDTE (M23)



paths.






GWDTE.



excavation.







permanent draining.


Low



16

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG22 –

WTG25

(690m)

M23 low

M25 low

M6 low

545m of track within/


(M23/ M25/ M6)

Local valley between WTG22 and

WTG25. On slopes near turbines

(330m), M23/ M25 and track

generally parallel to flow direction

therefore limited effect on proportion

of flow contributing to GWDTE.

Within valley, valley mire complex

including M25 and M6 with small

watercourse. Track perpendicular to

flow direction (215m) but flat/ low

gradient, therefore lower likelihood of

disrupting flow paths to GWDTE.








preserve existing flow paths/ ensure that track does

not act as preferential flow path.



track.




Low

WTG25 M23 low

M25 low


(M23/ M25)



paths.






GWDTE.



excavation.







permanent draining.


Low

WTG25 –

WTG24

(440m)

M23 low

M25 low

M6 low

440m within GWDTE

(M23/ M25, localised

M6)


dominant flow direction and on low

gradient with minimal disruption to

flow paths.








Low



17

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG24 M23 low

M25 low


(M23/ M25)



paths.






GWDTE.



excavation.







permanent draining.


Low

WTG24 –

WTG19

(470m)

M23, M25,

M6 low, M15

low

470m track within

GWDTE (M23/ M25/

M15, localised M6)

Track partially oriented parallel to

flow direction, with minimal influence

on flow paths contribution to the

GWDTE, and partially perpendicular

with disruption of flow paths.








preserve existing flow paths/ ensure track does not

act as a preferential flow path.



track.




Low



18

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG19 M23, M6

low, M15

low


(M23/ M15, localised

M6)



paths.






GWDTE.



excavation.







permanent draining.


Low

WTG22 –

WTG21

(346m)


GWDTE (M23)

Track oriented parallel to flow

direction, minimal influence on flow

contributing to the GWDTE.




ensure track does not act as a preferential flow path.


Low


(M23)



paths.






GWDTE.



excavation.







permanent draining.


Low



19

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG21 to

WTG20

(446m)

M23, M6

low, M15

low

446m track within

GWDTE (M23/ M15,

localised M6)

Track oriented parallel for part of

length, with minimal influence on

flow paths contributing to the

GWDTE, and perpendicular for part of

length, potentially disrupting flow

paths.












track.




Low

WTG20 M6 low, M15

low

Located within mosaic

consisting of 20%

GWDTE (M15/M6)



paths.






GWDTE.





excavation.







permanent draining.


Low



20

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG20 –

WTG13

(785m)

M23 low,

M10

medium

385m track within

GWDTE (M23, localised

M10)

Track partially parallel to flow path

with minimal influence on flow paths

contributing to the GWDTE, partially

perpendicular potentially disrupting

flow paths.





possible.








track.


Low

WTG13 M23, M25,

M6 low, M15

low, M10

medium

Located adjacent to

GWDTE (M23/ M25/

M15/ M6/ M10

mosaics)


downslope due to flow path

disruption and dewatering at turbine

foundations.

Potential effect on GWDTE adjacent

due to dewatering.

Crane pad located across linear M10

and M6 feature.

N High • Micro-siting away from more sensitive GWDTE


possible.



excavation.







permanent draining.


Low

Track to

WTG17

(600m)


GWDTE (M23)


direction, however location of spur

track on broad ridge minimises

potential disruption to flow paths.






Low



21

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk


GWDTE (M23)

Turbine on localised higher point with

dominant flow direction towards

valley to NE. GWDTE (M23) situated

to NW, potential influence on flow

contribution to GWDTE from

dewatering only.

N Low • Time excavations open minimised.


excavation.







permanent draining.


Negligble

WTG17 spur

to WTG16

(154m)


GWDTE (M23)

Track oriented parallel to dominant

flow direction, with minimal influence

on flow paths contributing to GWDTE.




ensure track does not act as a preferential flow path.


Low


GWDTE (M23)

Potential effect on GWDTE adjacent


foundations.

Turbine and crane pad located

adjacent to GWDTE but parallel to

flow paths and unlikely to have a

significant effect on overall flow

contribution.



excavation.







permanent draining.


Low

WTG16 –

WTG15

(345m)


GWDTE (M23)

Track transversal to dominant flow









Low



22

Infrastructure

element

GWDTE

sensitivity


loss of

GWDTE?

Pre-

mitigation

Risk


Risk

WTG15 M23 low Located up-gradient of

GWDTE (M23)


downslope due to flow path

disruption and dewatering at turbine

foundations.

N Medium • Time excavations open minimised.


excavation.







permanent draining.


Low

WTG15 to

WTG14

(470m)

M23 low 470m located within/


(M23)




affecting GWDTE downslope.

Y Medium






Low


(M23)



paths.






GWDTE.



excavation.







permanent draining.


Low



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3. MITIGATION MEASURES

Mitigation measures to minimise the potential impacts of the development on GWDTEs are provided for each

infrastructure element in Table 2.3, and are summarised below:

General:

• Micro-siting of infrastructure away from the more highly groundwater-dependent GWDTEs (M10 and M6)

will be undertaken where possible.

• It is proposed that the existing drainage and flow paths (shallow groundwater and surface water) will be

maintained around construction areas.

• Groundwater and surface water drainage arrangements for construction elements will be in line with the

principles of sustainable drainage systems (SuDS) by incorporating appropriate attenuation and treatment.

This approach will be in line with the SuDS Manual (C697) published by CIRIA and the CAR Practical Guide.

• Mitigation measures will be incorporated into the Environmental Management Plan for the site.

Excavations for turbine foundations and borrow pits:

• The time any excavation is open will be kept to a minimum to avoid ingress of water and dewatering.

• Temporary cut off drains will be installed to prevent surface water and shallow through-flow entering into

excavations. Clean water will be discharged downstream of the excavation and encouraged to infiltrate into

the ground mimicking natural flow patterns.

• Drainage or pumping from excavations will be minimised through appropriate design.

• Runoff and any water pumped from excavations in proximity to GWDTES will be discharged in proximity of

the excavation (mimicking natural flow patterns) after being passed through a SuDS feature. Infiltration of

flows will be encouraged (e.g. use of swales). Concentration of flows at the discharge point(s) will be avoided.

• Reinstatement of excavations will be reinstated as soon as practicable once construction works are complete

and will ensure that suitable hydrological conditions are restored, avoiding permanent drainage.

Track construction & drainage:

• All tracks will be constructed with a suitable camber and will have a permeable, granular surface.

• Tracks will be constructed from material of a suitable chemistry i.e. that will not have an adverse impact on

the local soil/ groundwater chemistry.

• Where the tracks are oriented parallel to the dominant flow direction, transverse drains (‘grips’) will be

constructed, where appropriate, in the surface of the tracks to convey runoff from the road into the drainage

ditch, thereby preventing the tracks from acting as preferential flow paths.

• Where access tracks are oriented perpendicular to the dominant flow direction the trackside drainage will

include a lateral drainage channel cut along the uphill side of the track to intercept the natural runoff and

shallow groundwater flow and this will be conducted under the track at regular intervals through cross

drains. The trackside drains will be broad and shallow with moderate gradients to prevent scouring. Flows

from this drainage will be treated by filtration through check dams and settlement at sumps.

• Where appropriate, swales will be used along the access tracks to hold water temporarily and to encourage

infiltration/discharge into the ground locally. Check dams will be placed regularly along the swales to reduce

flow velocities and maximise infiltration.

• All existing land drainage passing under the tracks will be preserved or reinstated to ensure that the existing,

drainage regimes are maintained. This includes all watercourses, drains, flushes, springs and peat pipes.

• Watercourse crossings will be designed to ensure that flows are not restricted or concentrated downstream.

• During the operation phase, any drains associated with tracks will be inspected periodically and cleaned out

as necessary.



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• Impermeable plugs at regular intervals will be used when backfilling cable trenches to ensure that the trench

does not act as a preferential pathway.

Oil, Fuel and Site Vehicle Use and Storage:

• Oil and fuel storage areas will be impermeable and bunded.

• No fuelling or maintenance of vehicles and machinery will be carried out within GWDTE and cleaning of tools

will be carried out in a designated area in line with PPG 7.

• Spill kits will be kept on site.

• Regular inspection and maintenance of vehicles, tanks and bunds will be undertaken.

• The Pollution Incident Response Plan for the site will include measures to deal with any accidental spillages.

Concrete

• Pouring of concrete for turbine bases will take place within well shuttered pours to prevent egress of

concrete from the pour area.

• Pouring of concrete during adverse weather conditions will be avoided.

• Concrete pH will be as close to background pH as practicable.

Sgurr Energy Ltd Linfairn Wind Farm Appendix 9.4 ... Dependent Terrestrial Ecosystems Risk...

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