Environmental Statement South Kyle Wind Farm August 2013

Transcription

1 15 PEAT, GEOLOGY AND CARBON BALANCE Introduction Methodology Desk Study Site Reconnaissance and Peat Probing Baseline conditions Results of Desk Study Mining and Quarrying Designated Sites Discussion of Peat Deposits Based on Site Reconnaissance Geological Impact Assessment Peat Slide Risk Assessment Peat Hazard Rating System Design Considerations Geotechnical Considerations Potential Construction Impacts on Peat Stability and Mitigation Head Loading Removal of toe support Adverse concentrations of water flows Other construction impacts Potential Construction Impacts on Geological and Soils Environment Design Mitigation Mitigation incorporated into the Proposal Access Tracks Loose Peat Geotechnical Risk Register Carbon Assessment and Peat Spoil Summary and Conclusions Page 1 of 16

2 15 PEAT, GEOLOGY AND CARBON BALANCE 15.1 Introduction 1 This chapter is an appraisal of the peat deposits found at the proposed South Kyle Wind Farm development area and provides a preliminary engineering geological assessment of the prevailing ground conditions as they relate to peat stability issues. A preliminary peat landslide hazard and risk assessment has been carried out which seeks to: identify any areas of enhanced peat slide risk which could be affected by the construction of the wind farm assess the severity of the hazard which would be caused by a peat slide and the likelihood of occurrence describe mitigation measures to reduce such risks to acceptable levels 2 A preliminary engineering geological assessment aimed at identifying any areas of geological interest or geological features of note within the application site has also been assessed. 3 The information and data collated from the peat and geological assessments has been used to inform site design and therefore minimise the potential impacts associated with the development of the Site Methodology 4 The methodology employed in the peat stability study generally follows the recommendations of the Peat Hazard and Risk Assessment Best Practice Guidelines (Scottish Executive December 2006) and draws on experience of similar appraisals for other wind farm projects. 5 An estimate of the risk of peat slides was undertaken at the South Kyle Wind Farm site by identifying the salient features of local bedrock, glacial drift deposits, geomorphology, topography, peat profile, peat strength, drainage, climate and weather that may influence slope stability. 6 The broad methodologies are discussed in the following sections. 7 The methodology applied in the geological assessment is a qualitative risk assessment methodology, in which the probability of an impact occurring ands the magnitude of the impact, if it were to occur, are considered. This approach provides a mechanism for indentifying the areas where mitigation measures appropriate to the risk presented by the proposed development. This approach allows effort to be focussed on reducing risk where the greatest benefit may result. The assessment of risk is outlined in Table 15.1 below. Page 2 of 16

3 Table 15.1 Matrix used to Estimate Geological Risk Probability of Magnitude of Potential Impacts Occurrence Severe Moderate Mild Negligible High High High Medium Low Medium High Medium Low Near Zero Low Medium Low Low Near Zero Negligible Low Near Zero Near Zero Near Zero Note: After Guidelines for Environmental Risk Assessment and Management Revised Departmental Guidance (DETR, 2000) 8 Where the magnitude of the potential impacts in terms of geology and soils are: Negligible No impact or alteration to existing geological environs or important soil settings (i.e. valuable agricultural land) Mild Some loss of peat and soil, but which has no long term impact Moderate Slope failure or instability which may cause foundation problems, damage to important geological structures/features (i.e. loss of extensive areas of peat and soil) Severe Slope failure or instability which results in loss of life, permanent degradation and total loss of important geological structures/features (i.e. peat bog environment across the entire development site) Desk Study 9 A desk-study was undertaken on peat slides in general and the occurrence of landslides in the region around the South Kyle Wind Farm site. Hazard models were developed which provide an estimation of the nature, size (magnitude) and frequency characteristics of peat sliding events deemed to have immediate background relevance to this study Site Reconnaissance and Peat Probing 10 A field survey in order to estimate the size, frequency, likelihood and consequences of peat slide events was undertaken. This identified any delineating specific hazard-prone areas or individual slopes within the proposed development site that are likely to be more prone to failure than others through the following: evidence of previous peat slide activity and slope instability as an indicator and guide to future ground movements by walkover inspections observations of sinkholes and investigation of sub-profile drainage by using a listening-stick measurements of peat depths by using a 5 m aluminium probe rod obtaining bulk samples by excavation of trial pits obtaining core samples using a gouge auger determinations of peat shear strengths using a Pilcon hand-vane field instrument measurements of slope gradients using a Suunto Type PM-10/360PCT Precision Inclinometer Page 3 of 16

4 Peat slide Hazard Rating System (PHRS) 11 Peat slide susceptibility was estimated using the Peat slide Hazard Rating System (PHRS) (Nichol, 2006). The principal features of the assessment criteria and scores are detailed in Appendix 15.1 (Volume 5). 12 The PHRS is a proactive tool to rationally address peat slide hazards and provide a defensible, standardised way to assess priority by numerically differentiating the apparent risk at potential peat slide sites. The principal features of the assessment criteria and scores for the hazard rating system are summarised in Table 2 of the South Kyle Peat Slide Hazard and Risk Assessment Interpretive Report, presented in Appendix 15.2 (Volume 5). 13 In the case of South Kyle, the PHRS procedure needed to be adapted to suit a forestry site where much of the ground is inaccessible and the use of conventional 100 m x 100 m or 200 m x 200 m grid based sampling stations proved impossible. Accordingly, further peat slide susceptibility investigations will be required once felling operations have been carried out at the proposed positions of turbines and along the routes of access tracks. 14 As such, the PHRS procedure was applied at 126 sampling stations across the site in order to provide a comparative method for ranking areas by peat slide geohazard potential. The position of sampling stations along the forest tracks were selected in this instance based on the size of the site, accessibility, the ground covered by previous investigations, the number of sampling stations and the findings of the desk study. 15 In addition, 561 probe positions from previous investigations were taken into consideration (refer to Figure 3 of the South Kyle Peat Slide Hazard and Risk Assessment Factual Report (the PSRA Factual Report ), presented in Appendix 15.1 (Volume 5) for further details) Peat Profile Logs 16 Detailed inspections were made using hand-dug trial pits and gouge auger holes at three locations, X1, X2 and X3, as illustrated on Figure 5 of the PSRA Factual Report, Appendix 15.1 (Volume 5) Sample Collection 17 Two representative samples of peat were collected at peat profiles X2 and X3. These were quartered, with one quarter being sent to Jacobs Engineering Laboratory for determination of moisture content, one quarter used for microscopic examinations and the remaining quarters stored for future reference Peat slide Inventory 18 Since previous peat slide activity around the wind farm site may serve as an indicator and guide to future slope movements, evidence of peat slope instability was sought in the field by walkover inspections. No noteworthy peat slides were identified. Page 4 of 16

5 Peat Depth and Strength 19 The peat probing results obtained during the PHRS survey were combined with the measurements collected during the previous peat probe surveys (Appendix 15.2, Volume 5) to give a grand total of some 687 peat depth values which were used to create a peat depth contour map to depict the patterns of variation in peat depth across the development site (Figure 15.1, Volume 3). 20 Peat strength was estimated at selected sampling stations using a hand shear vane, and at the bulk of the stations using the penetration of a probe as a rough guide Terrain Analysis 21 One of the simplest and most efficient methods of evaluating peat slide risk involves the application of terrain evaluation procedures. The observational method used in this study was based primarily on the combined assessment of geomorphology, topography and geology by a professional geotechnical engineer. However, other peat slide attributes of secondary importance were also taken into consideration, including orientation to the wind, orientation to the sun and forest cover. 22 The zones do not predict where peat slides will occur during the next rainfall event. Instead it can be expected that over time, high susceptibility zones will experience more peat slides than lower susceptibility categories. 23 The analysis included both desk studies and field investigations. Three classes of peat slide susceptibility were adopted: Category I for low to very low susceptibility Category II for moderate susceptibility Category III for high to very high susceptibility 15.3 Baseline conditions Results of Desk Study Geography, Topography and Geomorphology 24 The proposed wind farm development site occupies a rural setting in extensive commercial forestry on the northern edge of the Southern Uplands. The hilly ground comprises a complex topography with smooth, rounded hills covered with conifer trees. At the proposed development, the uneven upland lies between 200 and 525 m above sea level with the highest point, McCowans Knowe (5242 m AOD) at grid reference NS In general, the ground slopes vary from very gentle,with broad almost level watersheds, to steep slopes on local rocky knolls and on the rounded summits of the principal hilltops. Over much of the peatland study area, gradients average around 5 o. The peatland occupies several geomorphologies, but it dominates in the broad tracts of ground lying between the principal hilltops and across the headwaters and along the valleys of the principal watercourses. The peat Page 5 of 16

6 varies in depth according to local topographic conditions, with pockets of deep peat linked by shallower and more extensive peat units. In addition, the peatland appears severely degraded by forestry activities. Natural erosion of the peatland gives rise to minor disruption of the ground surface in a few places. 25 Generally, surface water drains along a number of streams flowing either northwards into the River Nith, westwards into the River Doon or southeastwards into Water of Deugh. 26 The south-western boundary of the site lies to the northeast of the A713 road from Ayr to Castle Douglas. 27 Much of the landscape surrounding the proposed development was created during complex phases of glaciation affecting this region in Late Pleistocene (Devensian) time (approx 10,000 BC). The movement of glaciers carved and moulded the rocks and left behind varied accumulations of glacial deposits. Glacial landforms range from upland fringe hills to river valleys. 28 Geomorphological observations made during desk studies, the walkover and PHRS field surveys are discussed within the relevant sections of this report, in particular Section 3 on ground conditions and material properties Geology 29 Geologically, the district is part of the extensive outcrop of early Palaeozoic strata which forms the Southern Uplands Terrane and the development site itself straddles the Southern Upland Fault (SUF), a major tectonic feature of regional significance. At the proposed development, the oldest rocks cropping out to the southeast of the SUF are greywackes (turbidites) sandstones, siltstones and shales of Ordovician (Caradoc & Ashgill) age that generally strike northeast and dip steeply southwards. To the northwest of the SUF a complex, fault-bounded block of mixed rocks of sedimentary, igneous extrusive and igneous intrusive derivation appears, associated with the SUF. The lavas (mainly basalts and andesites) form extensive outcrops across the northern portion of the development site. The bedrock is overlain by mixed deposits of drift, of glacial derivation, and tracts of peatland of postglacial age. 30 The slopes are expected to be mantled by a thin cover (1 m to 2 m) of modified till and superficial deposits consisting of clayey silts and silty clays, with a variable gravel, cobble and boulder content. Extensive areas of peat appear widespread. The deposits of peat usually overlie glacial drift but in a few places, particularly on higher ground, they may rest directly on bedrock or weathered bedrock (refer to Appendix 15.2, Volume 5 for further details) Drift Geology 31 An extract of the published drift geology map for the area is shown on Figure 15.2 Drift Geology (Volume 3). 32 The drift geology comprises peat deposits that are present across the majority of the elevated ground, with Glacial Till on the lower valley slopes and thin ribbons of alluvium present in the valley bottoms. Page 6 of 16

7 33 The peat deposits are Post-Glacial and therefore overlie the Glacial Till. No drift deposits are indicated on the areas of highest ground where the solid geology is at outcrop. 34 The Glacial Till at the Site is reported to consist of brown and grey brown, heterogeneous, silty, sandy, gravelly till (boulder clay). The tills are generally very compact, poorly stratified, matrix-supported diamictons, containing angular to rounded clasts up to boulder size Solid Geology 35 An extract of the published solid geology map for the area is shown on Figure 15.3 Solid Geology (Volume 3). 36 The solid geology under majority of the site comprises Ordovician greywackes and shales with occasional conglomerates, mudstones and cherts. The Ordovician deposits represent the oldest rocks of the region and are shown on to be highly inclined towards the south and south-east. The limit of outcrop of Ordovician strata is marked by the SUF, which is aligned north-east to south-west through the northern part of the application site. 37 To the north-west of the SUF a band of predominately igneous extrusive rock is at outcrop, comprising basalt and basic andesite. This outcrop extends between the SUF and the Dalmellington Fault (DF) to the north. The DF is also aligned north-east to south-west and passes close to the northern boundary of the application site. The igneous extrusives are accompanied by sandstones and conglomerates of the Lower Old Red Sandstone. The SUF and DF both down-throw to the north-west. 38 In the most northern part of the Site, the solid geology comprise strata of the Lower Coal Measures. The Lower Coal Measures form part of the Carboniferous Coal Measures, which are extensive to the north of the Site and are characterised by cyclic sequences of sandstone, mudstone, siltstones, coals and seatclays Mining and Quarrying 39 The Coal Authority has confirmed that no coal mining has taken place or is presently being carried out within the proposed development and advised any future workings, either on or beneath the surface are considered unlikely. 40 No evidence of metal mining was detected during the peat investigation and borrow pit surveys Designated Sites 41 There are no geological designated or protected sites within the application boundary. 42 Benbeoch SSSI is located 1.5 km NW of the Site Boundary and is designated for its geology which provides an example of alkali-enriched basaltic rocks. It extends to an area of about 83 ha. Page 7 of 16

8 Local Climate 43 The South Kyle Wind Farm district has an unsettled cool climate, with unevenly distributed annual rainfall and strong winds. Total annual average rainfall appears somewhat higher than expected compared to much of the Scottish mainland. However, levels of rainfall reduce rapidly from west to east. Like much of Scotland, the South Kyle Wind Farm district may receive prolonged and heavy rainfall in any one month but cloudbursts appear more common during the late summer, autumn and early winter months. Typically, April and May are comparatively drier months (refer to Appendix 15.2, Volume 5 for further details) Seismicity 44 For the South Kyle Wind Farm district, the Eurocode 8 seismic hazard zoning maps for the UK (Musson and Sargeant, 2007) indicate that horizontal Peak Ground Acceleration (PGA) values with 10% probability of being exceeded in 50 years (475 year return period) are generally less than 0.02 g, which is exceedingly low. Accordingly, in relation to the present study, seismic tremors are unlikely to induce mass movements in peat, in either marginally stable slopes or saturated peatland areas Discussion of Peat Deposits Based on Site Reconnaissance Peat Profile 45 The peat profile at the proposed development comprises of a layer of brown fibrous sphagunum-eriophorum peat between the present-day root mat at the top and the boundary with the underlying material at the bottom. Generally, the layer of peat possesses a textile-like fabric with relatively good engineering characteristics. 46 Exposed faces in stream banks, trackside cuttings and drainage ditches reveal a crude banded or laminated structure in the peat profile, with marked variations in thicknesses of individual layers over short distances. Typical moisture contents range from 300% to 1000%, but in localised pockets the moisture content is considerably higher. The moisture contents determined by laboratory testing for selected samples were 586% and 654% respectively (refer to Appendix 15.2, Volume 5 for further details) Peat slides at the proposed South Kyle Wind Farm 47 No noteworthy peat slides were identified on site. Several minor instances of slumping below 5 m diameter in size were observed along the banks of watercourses, but these are considered to be normal as part of watercourse development Analysis of Peat Depths and Strengths 48 The depth of peat at South Kyle ranged from 0.01 m to 2.72 m, with values less than 1.0 m commonplace. Deeper peat, exceeding 1.0 m was found at 18 sampling stations (14%) and exceeding 1.5 m at eight sampling stations Page 8 of 16

9 (6%). Values exceeding 2.0 m were only found at three sampling stations, the deepest at sampling station 89 on the eastern side of the site. 49 Peat strength values varied between 20 and 50 kpa, depending on degree of saturation, but typically fell within the range kpa. A wide scatter of results also existed and no noteworthy patterns were detected through the peat profile. Interestingly, the previous investigation by Young Associates (2004) included the collection of some 800 shear vane measurements at 250 and 500 mm depths, with an average value at both depths of 25 kpa. Most of the shear vane results (~75%) were below 30 kpa with the lowest values associated with the wettest ground (refer to Appendix 15.2, Volume 5 for further details) Sinkholes and Drainage 50 No sinkholes were identified at the South Kyle Wind Farm site. 51 The natural drainage characteristics have been affected in some areas by man-made drainage channels. A mixture of widely and closely spaced field drains cross much of the site and, although they are in a degraded condition, are effective at draining surface water. 52 Active sub-surface drainage pipes are present on site. Based on surface observations and using the scale given by Jones (1978), the pipe frequency across the bulk of the development site is estimated at 5-10 per km 2 but increasing to about per km 2 in the north-western portion of the site Terrain Analysis 53 The terrain analysis indicated that the site is Category I (low to very low susceptibility to peat slide risk) Geological Impact Assessment 54 Details of the components of the proposed development are provided in Chapter 4 Description of the Proposal. The key components relevant to the geological assessment are: 50 no. wind turbines with associated foundations and crane pad hardstanding permanent access roads from, to and between turbines (including upgrades to existing forestry tracks and additional cut and floating road sections) 22 no. new and existing watercourse crossings associated with the access roads installation of electrical and communication cables adjacent to the access roads construction of an electricity substation compound and control building 6 no. permanent wind monitoring masts with associated foundations and access road forest felling 3 no. temporary site compounds including temporary concrete batching plants Page 9 of 16

10 2 no. temporary storage areas 8 no. borrow pits a permanent welfare facility for use during the operational phase of the wind farm 55 The proposed design will be assessed against the potential to impact upon the geological and soils environment during construction, operational and decommissioning phases Peat Slide Risk Assessment Peat Hazard Rating System 56 A PHRS score of 152 for the entire South Kyle Wind Farm site was calculated as the arithmetic average for the sampling stations. As a rule of thumb, a PHRS rating of less than 200 is assigned a low priority, while a rating of more than 400 is in need of urgent attention. 57 Almost all of the PHRS scores fall within the low range for peat slide risk. For comparison purposes, PHRS scores of 373, 482 and 434 apply in relation to the well-established peat slide localities at Morsgail, Isle of Lewis, Scotland (Bowes, 1960), Derrybrien, Galway, Republic of Ireland (Fleming 2003) and Hart Hope, North Pennines, England (Warburton et al, 2003), respectively. 58 Only two of the sampling stations received PHRS scores greater than 200 (46 and 81), with sampling station No 81 receiving the highest score of Design Considerations 59 Site constraints have been identified by combining the results of the terrain analysis and the PHRS and it is recommended that a maximum slope gradient of 10º is adopted. 60 Areas of exceedingly wet ground and pockets of deep peat were identified to the northeast of Meikle Hill in the north-eastern portion of the site, and to the south of Clawfin Hill in the north-western portion of the site. It is recommended that these areas should be avoided as far as possible. 61 In addition areas of disturbed ground appear mainly associated with incised ground in the vicinity of watercourses, and so the adoption of a set-back distance of at least 50 m from watercourses is strongly recommended. Special care needs to be taken in the design and construction of crossing points on watercourses Geotechnical Considerations 62 Failure occurs, and peat slide initiation is possible, when the combined forces from the downslope (slope parallel) weight of peat (shear force) equal or exceed the shear strength in a weak layer or the boundary between layers. However, strong variations in peat properties (and stability) across slopes pose difficulties and so there is always residual uncertainty. Page 10 of 16

11 63 The various methods available for analysis of slope stability involve the factor of safety, which is the ratio of resisting forces to the driving forces acting on a mass of peat on a potential failure surface: F = Resisting forces ( strength ) Disturbing forces ( stress ) 64 Thus, for a given failure mode, calculation of the Factor of Safety (F) in excess of 1.0 indicates that the slope is at least in equilibrium. Conversely, F values of less than 1.0 indicates that failure of the type considered is likely. 65 Typically, the Factor of Safety methodology is used for assessments of specific slopes of up to about one hectare in size. Generally the method is somewhat cumbersome for sites such as the South Kyle Wind Farm which is more extensive, with variable slope morphologies. However, using the SLIPEX program developed by Greenwood (2006), in connection with the EU funded ECOSLOPES project for routine stability analysis, and the assessment of the contribution of vegetation to slope stability, a reconnaissance survey of F values across the site at South Kyle indicates that the slopes would be stable. 66 Stability analyses were modelled for a typical slope of 5 o and a worst case scenario slope of 10 o. With typical Phi = 25 o, F values show the slopes would remain stable (Appendix 15.2, Volume 5). The modelling confirms that peat sliding is highly improbable within the proposed design constraints at the South Kyle Wind Farm Potential Construction Impacts on Peat Stability and Mitigation 67 Although the peat slide risk at South Kyle appears low to negligible, the potential effects of the construction of the wind farm infrastructure that might influence peat stability need to be considered as a matter of prudence. The potential effects of construction on peat slide risk are threefold. The first involves concentrated loads, such as material from turbine foundation excavations, being placed on marginally stable ground at the top of a slope. The second involves removal of toe support at the bottom of a slope and the third entails the adverse concentration of water flows within a slope or into unstable excavations. 68 These matters are discussed below and elaborated in the Geotechnical Risk Register presented as Appendix 15.2 (Volume 5) Head Loading 69 Concentrated loads, such as excavated material placed on the slope, create the single most adverse effect on the stability of a slope. Accordingly, during the construction phase, all excavated materials should be removed to temporary storage mounds, positioned off-slope, at a safe position certified by a geotechnical engineer. 70 Loading associated with the construction of floating roads may, in certain cases, lead to unstable ground conditions. Accordingly, during the construction phase all tracks will, as far as possible, be constructed under geotechnical supervision and monitored during and after construction. Page 11 of 16

12 Removal of toe support 71 Excavation of the slope for turbine foundations or excavated tracks may remove toe support and increase potential for ground movements involving peat. However, the adverse effect on F values appears small (<10%) and any localised movements will be into the new excavation, and thereby contained. Excavations for tracks will be backfilled with free draining granular rock material Adverse concentrations of water flows 72 Disturbance to the natural drainage system may increase potential for peat instability. However, the design will incorporate substantial improvements to the drainage of the site, and since peat sliding almost invariably involves increased pore water pressures, it follows that robust drainage plans and engineering control of water during the development will result in a significant overall reduction in the risk of peat instability Other construction impacts 73 Peat slide potential also increases with: rockhead smoothness clayey subsoils that impede water flows and provide smooth slip-surfaces localised steep gradients presence of solifluction planes improvements such as drainage works localised erosion features such as animal paths and stream channels 74 Accordingly, construction activities will be carried out under geotechnical supervision as required, and protection measures will be implemented using the observational method Potential Construction Impacts on Geological and Soils Environment 75 The following paragraphs present a summary of the key geotechnical/geological issues that could be encountered during the development, operation and decommissioning of the proposed development. The potential impacts are discussed in terms of the design which incorporates the mitigation measures, including micrositing. These are summarised in Table A total of 8 borrow pits have been selected on site offering sufficient materials for access tracks, crane pads and (if suitable) aggregate for concrete bases, as detailed in Appendix 21 Monitoring, Management and Mitigation (Volume 5). The borrow pits have been selected to give a geographic spread over the site. Each borrow pit location is situated on outcropping rock, or where there are limited or no soils overlying the resource. 77 The borrow pits would require blasting/ripping to win materials, this would require to be managed in accordance with Planning Advice Note 50, Controlling the Environmental Effects of Surface Mineral Workings. Development of the borrow pits would have negligible impact on the Page 12 of 16

13 geological environment as their extent is small, the probability of occurrence is high and thus the estimated overall risk to the geological environment is considered to be low. 78 There is potential for instability of proposed buildings, structures and turbines due to inappropriate foundation design and movement along any of the existing geological faults. It is considered that, with the proposed wind farm design, the probability of occurrence is low and the magnitude of the impact is moderate. The overall impact is considered therefore to be low within the context of the current design and geological setting, where good foundation conditions exist (glacial till or bedrock) and the proposed turbines, structures and buildings are located away from major geological faults. 79 Peat slides are a potential risk, but is a risk that the proposed design has been mitigated by site design and the mitigation measures indentified in the peat slide risk assessment discussed within this chapter and Appendices 15.1 and 15.2 (Volume 5). 80 Table 15.2 confirms that the proposed design would not have a significant impact on the geological and soils environment during construction, operational and decommissioning phases. 81 There is no risk to the offsite Benbeoch SSSI which is noted for its geological interest. Table 15.2 Summary of Potential Impacts Potential Spatial and Impact Temporal Impact Borrow Pits Rock Extraction Ground Movements/insta bility of foundations for turbines, structures and buildings Peat Slide Risk Carbon and Materials Local, short long term Local, short long term Local, short long term Local, short long term Probability of Occurrence Magnitude of Impact Significance of Impact Mitigation Incorporated into the Design High Negligible Low Develop in accordance with PAN50 Low Moderate Low Peat slide assessment to inform appropriate design Additional Mitigation Required? Restoration of pits, remove steep faces Site Investigatio ns to inform foundation design & possible micrositing following Site Invetsigatio n Addressed in Peat Slide Risk Assessment (Chapter 15, Appendices 15.1 and 15.2) Addressed in Carbon and Peat spoil balance calculations (Chapter 15 and Appendices 15.3 and 15.4) Page 13 of 16

14 15.8 Design Mitigation Mitigation incorporated into the Proposal 82 The design for the proposed development has been progressed and refined as an iterative process. Through each iteration, consideration of best practice guidance has been incorporated with mitigation measures which address geological and soils constraints. 83 The site walkover and peat probing exercises assisted in developing the track and turbine layout to avoid potential areas of concerns, essentially where the peat thickness in conjunction with steeper slopes pose a potential risk of peat slides. 84 The internal track layout originating from the existing access tracks has been developed to minimise the construction of the tracks on steep gradients and where practical to avoid crossing natural drainage features. Where the access tracks do cross natural drainage they have been designed to be perpendicular to flow direction Access Tracks 85 New access tracks will follow routes parallel to slopes and avoid steeply sidelong ground as far as possible. All access tracks will be approved by a geotechnical engineer before construction commences, and the provision of special drainage measures may be required Loose Peat 86 The excavation of peat will require a series of subsoil storage mounds and the guidance in Garrard & Walton (1990) and Geoffrey Walton Practice (1991) will be followed. It is strongly recommended that the storage sites are selected on the basis of geotechnical criteria, and the design and construction of the subsoil storage mounds are supervised by a geotechnical engineer Geotechnical Risk Register 87 A geotechnical risk management system will be adopted during detailed design and construction as part of the overall risk assessment. This will be a live document which, once commenced, continues through to project completion, incorporating new risks as they are discovered Carbon Assessment and Peat Spoil 88 Following Scottish Government guidance on wind farm carbon savings (Scottish Government, 2012a), a detailed carbon assessment has been undertaken for the site using the Scottish Government Windfarm Carbon Assessment Tool Version (Scottish Government, 2012b) in order to calculate these losses and determine the net expected carbon savings. The carbon assessment tool output for the Proposed Development is provided as Appendix 15.3 (Volume 5). Page 14 of 16

15 89 Assuming a capacity factor of 27%, as advised within the Scottish Government Windfarm Carbon Assessment Tool, it is estimated that the annual energy output from the wind farm will be in excess of 350,000 MW per year or 8,750,000 MW over the 25 year life span of the wind farm. 90 Initial site specific calculations suggest that approximately 418,000m 3 of peat will be excavated during construction of the proposed development. This value is supported by the Scottish Government Windfarm Carbon Assessment Tool Version that conservatively estimated almost 424,000m 3 of peat is to be excavated. Calculations also estimated that approximately 427,000m 3 of peat will be required for the restoration of the proposed development following construction, hence all of the organic material excavated as part of the proposed development can and will be reused on site during restoration (refer to Appendix 15.4, Volume 5 for further details regarding peat spoil balance calculations). 91 The output of the carbon assessment indicates that the proposed development would result in emissions of 565,985 tonnes of carbon dioxide (tco 2 ). This equates to a carbon saving of over 300,000 tco 2 compared to equivalent coal fired electricity generation and over 200,000 tco 2 compared to equivalent mixed fossil fuel electricity generation. 92 The carbon assessment tool indicates that it would take approximately two and a half years for the proposed development to pay back its own carbon emissions (based on the indicative 350,000 MW annual energy output and the principle of displacing fossil fuel mix electricity as noted above). 93 It should be noted that the carbon calculator indicates significant total CO 2 losses due to losses from felled forestry (236,000 tco 2 eq.) and soil organic matter (222,000 tco 2 eq.). However, it is intended that significant forestry replanting will be undertaken (following final agreement with the relevant landowners) and restoration of any excavated peat and peaty soils as part of the site Peat Management Plan Summary and Conclusions 94 The South Kyle wind farm development site has an expanse of peatland which covers bedrock of Ordovician greywackes, sandstones, siltstones and shales, Devonian extrusive igneous rocks mainly basalt and andesite and Late Pleistocene glacial till deposits. 95 A desk-top study, peat sampling and site surveying was undertaken to determine the characteristics of the peat at South Kyle site and evaluate the risk of peatslide. 96 The desk-top study also aimed at identifying any areas of geological designations, areas of geological interest or geological features of note. 97 This assessment determined three principal design constraints: steep slopes should be avoided and as far as possible and development operations restricted to areas having gradients of less than 10º areas of wet ground and deep peat to the northeast of Meikle Hill in the north-eastern portion of the development site and to the south of Clawfin Hill in the north-western portion of the development site should be Page 15 of 16

16 avoided as far as possible. Departures are allowed provided encroachments are assessed for peatslide risk by a geotechnical engineer and provision is made for ground improvement areas associated with incised watercourses throughout the development site should be avoided as far as possible and adoption of a set-back distance of at least 50 m from watercourses is recommended. Departures are allowed, subject to contingencies being implemented 98 Particular care is required in relation to the detailed design of proposed crossings of watercourses. 99 Various short-term and long-term strategies and measures exist for peatslide risk control purposes and include a comprehensive range of engineering responses to deal with peatslide problems. These strategies can be managed using the geotechnical risk register (appended) and implemented during construction under geotechnical supervision. 100 On the South Kyle Wind Farm site, the elements at risk may be classified broadly into two categories: (1) environmental impairment and (2) impacts on land, buildings and roads. Overall, based on the findings of the PHRS scores, the level of potential damage or degree of loss of both elements appears low. 101 The geological assessment showed that there are no designated sites of geological interest or geological features of note within the application boundary, concluding that during construction, operating or decommissioning of the proposed development there will no significant residual impact affecting site geology. 102 The PHRS scores will be used as part of a constraint based design process, which ideally will avoid any area of moderate or high peatslide risk. If any site infrastructure is proposed in the vicinity of areas where the peatslide risk is higher (e.g. E10 & K6), then further ground investigation or detailed peatslide assessments will be required. Page 16 of 16