appendix 11a peat probing results - stornoway...

Stornoway Wind Farm Environmental Statement (May 2015) Peat

Appendix 11A

Peat Probing Results

Stornoway Wind Farm Factual Trial Pit Report

09 May 2014 Lewis Wind Power Limited

c/o EDF Energy

Adam Buchanan, Assistant Geotechnical Engineer

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Stornoway Wind Farm 09 May 2014

Client Details Contact John Penman Client Name Lewis Wind Power Limited Address c/o EDF Energy

Issue Date Revision Details A 09/05/2014 First Issue for review

NATURAL POWER CONSULTANTS LTD, THE NATURAL POWER CONSULTANTS LTD, NATURAL POWER SARL, NATURAL POWER LLC, NATURAL POWER S.A, NATURAL POWER SERVICES LTD AND NATURAL POWER OPERATIONS LTD (collectively referred to as “NATURAL POWER”) accept no responsibility or liability for any use which is made of this document other than by the Client for the purpose for which it was originally commissioned and prepared. The Client shall treat all information in the document as confidential. No representation is made regarding the completeness, methodology or current status of any material referred to in this document. All facts and figures are correct at time of print. All rights reserved. VENTOS® is a registered trademark of NATURAL POWER. Melogale™, WindCentre™, ControlCentre™, ForeSite™, vuWind™, WindManager™ and OceanPod™ are trademarks of NATURAL POWER.

Copyright © 2014 NATURAL POWER.

Local Office: Registered Office:

The Green House Forrest Estate, Castle Douglas

Dumfries and Galloway, DG7 3XS Tel: +44 (0) 1644 430 008

Registered Company No. SC177881 VAT No. GB243692648

The Green House, Forrest Estate Dalry, Castle Douglas, DG7 3XS SCOTLAND, UK Tel: +44 (0) 1644 430 008

Document history

Checked Allan Rutherford 05/05/2014 Approved Allan Rutherford 09/05/2014

Author Adam Buchanan 02/05/2014

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Stornoway Wind Farm 09 May 2014

Contents 1. Introduction ....................................................................................... 1

1.1. General .................................................................................... 1 1.2. Purpose of Investigation........................................................... 1 1.3. Previous Reports...................................................................... 1

2. Site Description ................................................................................. 2 2.1. Site Location and Setting ......................................................... 2 2.2. Topography .............................................................................. 2 2.3. Hydrology and Drainage .......................................................... 2 2.4. Historical Development of the Site ........................................... 2 2.5. Published Geology and Hydrogeology ..................................... 2

2.5.1. Superficial Geology .................................................... 2 2.5.2. Bedrock Geology ........................................................ 3 2.5.3. Hydrogeology ............................................................. 3

3. Development Proposals .................................................................... 3 4. Summary of Site Investigations ......................................................... 3

4.1. Form of Investigations .............................................................. 3 4.2. Trial Pit Investigation ................................................................ 4

Appendices ................................................................................................. 5 A. Trial Pit Photos 5

Appendices ............................................................................................... 88 B. Trial Pit Logs 88

Appendices ............................................................................................... 89 C. Trial Pit Locations Map 89

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Stornoway Wind Farm 09 May 2014 1

1. Introduction 1.1. General Natural Power was appointed by Lewis Wind Power Limited in February 2014 to undertake a geotechnical trial pit investigation at the site of the consented Stornoway wind farm on the Isle of Lewis.

Prior to the site investigations, Natural Power also completed a detailed Geotechnical Desk Study report for the site, a site wide topographic survey and detailed peat probing on the consented wind farm and localised micro siting options.

The trial pit investigations were undertaken by Natural Power for and on behalf of the Client during February 2014. The site work was overseen by an Engineer from Wind Prospect Limited representing the clients design team.

The main objective of the work was to assess the ground conditions at each turbine location and other key infrastructure locations in order to facilitate detailed geotechnical design.

The ground investigation scope was designed by Natural Power, and was carried out generally in accordance with the current Eurocode 7 and British Standards.

The ground investigation comprised the following elements: Trial pit investigation

Bulk samples have been taken however; geotechnical laboratory testing has not yet been commissioned at the time of this report. The bulk samples are being held by Natural Power and are available for geotechnical testing should this be required.

This Factual Trial Pit Report describes the site investigation procedures and field data obtained during the works.

1.2. Purpose of Investigation The ground investigation was undertaken to determine the following: Ground conditions across the site (including the geotechnical behaviour of the geological units) An indication of the groundwater regime across the site

1.3. Previous Reports Table 1 indicates the previous reports for the site undertaken by Natural Power that have been referenced in the preparation of this report.

Table 1: Previous Reports Document: Report reference: Issue date: Stornoway Wind Farm, Geotechnical Desk Study Report

1042038-A November 2013

Stornoway Wind Farm, Trial Pit Risk Assessment and Method Statement (RAMS)

1050929-A February 2014

Emapsite Utility Report 1046043 November 2013

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2. Site Description 2.1. Site Location and Setting The site is situated on the Isle of Lewis, in a semi-remote environment approximately 2.5km to the west of the centre of Stornoway at its closest point, and is centred on approximate national grid reference 137149E, 933373N. The site covers an area of approximately 1,700ha.

The site is located within an area of open peat bog moorland with intermittent areas of woodland, and includes a large number of streams, lochs, lochans and interconnecting watercourses.

Site access is from the pre-identified points on the A858, and from the A859 directly opposite Marybank Quarry and Creed Enterprise Park, to the east of the main turbine area. Internal site access is only available via pre-existing site tracks, or off road using ATV vehicles.

2.2. Topography The site essentially comprises a low lying, locally undulating topography. Site elevations are generally between 50-70mAOD, increasing slightly to around 100mAOD at the higher ground at the very north of the site. Natural Power has undertaken a detailed topographic survey of the site, which has been provided to the client.

2.3. Hydrology and Drainage Due to the topography of the site there is a complex pattern of hydrological catchments. There are numerous burns, lochans and lochs interconnecting with each other on the site. Two main river systems cross the site in an east-west direction (Abhainn Ghrioda and Abhainn a Ghlinn Mhoir), with numerous tributaries. These generally flow towards the main lochs, which ultimately drain eastward into Stornoway Harbour.

Water retaining peat bodies also cover the majority of the site. As the peat is generally saturated throughout the year, it is likely that there is little rainfall infiltration to ground, and therefore most rainfall will become surface runoff.

2.4. Historical Development of the Site The historical development of the site was discussed in detail within the Geotechnical Desk Study Report for the site. This indicated the site has been largely undeveloped open moorland with small scale infrastructure and water crossings since the OS records began.

Several small scale localised historical gravel quarries have also been present on site; these were mainly shown only on the early edition maps from 1852 to 1897 and were located adjacent to road and track routes. In addition, Bennadrove landfill site was developed on the north west of the site between 2002 and 2012, however is outwith the development area.

2.5. Published Geology and Hydrogeology

2.5.1. Superficial Geology The BGS data indicated the superficial deposits at the site are likely to comprise accumulations of peat. Detailed probing carried out by Natural Power indicated depths of between 0-6.0m Generally, thicker accumulations of peat are anticipated in low lying and wet areas, with thinner deposits on the higher ridges and slopes.

Previous works reviewed by Natural Power indicated a thin (typically <1.0m except in localised areas) layer of granular glacial till was anticipated to be present below the peat across the site. The conditions found on site differed from that anticipated with a much thicker layer of glacial till present comprising sands and gravel. The majority of trial pits were terminated within this stratum.

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2.5.2. Bedrock Geology The BGS data indicated the site is underlain by rocks of the Outer Hebrides Thrust Zone Mylonites Complex.

The vast majority of the site is shown to be underlain by Gneiss with a marked cataclastic fabric. A smaller area on the western boundary of the site is underlain by a “Mashed Gneiss” with the original banding largely destroyed. Ultimately these descriptions indicate the rock units to be intensely deformed crystalline, meta-sedimentary and igneous sourced lithologies. The banding and foliations likely to be present within the rock mass will influence rock mass behaviour and strength characteristics. The age and origin of these rocks is uncertain and is estimated as being between 545Ma and 4600Ma.

There are no significant faults indicated within the site boundary in the BGS data, there may be however, small areas of localised faulting.

Bedrock was found to be fairly consistent across the site and near surface along ridge lines and areas with steeper topography. The majority of trial pits were however, terminated within the glacial till due to refusal or reaching the maximum reach of the 8t excavator.

2.5.3. Hydrogeology The BGS 1:625,000 scale digital hydrogeological database shows that the site is underlain by low productivity aquifers of the Lewisian Complex. Groundwater is only likely to be present in near surface weathered zones and in secondary fractures.

3. Development Proposals The site is being developed by Lewis Wind Power Limited. Planning consent for Stornoway Wind Farm was granted in September 2012. The site has consent for 36 Wind Turbine Generators and associated infrastructure, including crane hard standings, up to 28km of access tracks (including watercourse crossings),up to 10 borrow pits, a substation compound, 2 permanent meteorological masts, underground cables, a number of temporary construction compounds, temporary peat storage areas and modifications to junctions interfacing with the local road network for two site entrances from the A859. It is understood a micrositing allowance of up to 50m is applicable.

4. Summary of Site Investigations 4.1. Form of Investigations The ground investigation scope was designed by Natural Power to meet the client’s requirements. The ground investigation was undertaken generally in accordance with the following standards: Trial pit investigation:

– BS EN 1997-2:2007 – BS EN ISO 22475-1:2006 – BS EN ISO 14688-1:2002 and 14688-2:2004 – BS EN ISO 14689-1:2003

Laboratory and in situ testing: BS EN 1997-2:2007, BS 1377 and ISRM soil testing and rock testing standards.

Site safety was managed in accordance with Natural Power’s RAMS document, and relevant UK legislation relating to the Health and Safety at Work Act 1974.

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4.2. Trial Pit Investigation Natural Power undertook a trial pitting investigation on site based on a scope of works designed by the client’s design engineer. Trial pits allow the detailed inspection, logging, sampling and in-situ testing of the superficial deposits and (depending on site conditions) bedrock, and the assessment of near surface groundwater conditions.

A total of 82 trial pits were undertaken at the site. The trial pitting was carried out by Natural Power employing a locally hired 8 tonne low ground pressure wide tracked 360 excavator.

A smooth edged ditching bucket was used to excavate the upper 1.0m of each trial pit, in order to allow the on-site archaeologist to assess the pits. The archaeologist having assessed the site during the first week of trial pitting deemed it unnecessary to have an archaeologist to overview all the remaining trial pits being undertaken on the site.

A bespoke trial pitting plan was provided by the client’s design engineer and agreed on site to avoid trial pitting in areas of deeper peat. This was to avoid conducting trial pits in areas where the peat would exceed the reach of the excavator and thus provide little additional information on the ground conditions over and above the pre-existing Natural Power peat probe data. Additionally access routes were predetermined to avoid areas of deeper peat and reduce the risk of sinking the excavator. A smaller 8 tonne excavator was employed for this reason. At the clients request sensitive water courses were also avoided to reduce the risk of silting due to fish spawning taking place during the trial pit investigation.

A trial pit was excavated at each turbine location to determine the general ground conditions at the turbine base and the adjacent crane pad area. Pits were also undertaken at regular intervals along the access track route and at the met mast and selected borrow pits.

The trial pits were excavated to a maximum depth of 3.4mbgl, and were logged by an experienced Natural Power Geotechnical Engineer. The pits were generally terminated at the full depth reach of the excavator or upon refusal on suspected bedrock, and at shallower depths for the track trial pits. Representative large bulk disturbed samples were collected from the trial pits as the excavations proceeded for geotechnical materials testing. The trial pits were backfilled immediately following completion of the logging and sampling works and the ground was reinstated as best as practically possible.

The trial pit photos are presented in Appendix A and the trial pit logs in Appendix B. The trial pit locations are shown on map number GB200383_M_003_A3 which is presented in Appendix C, which also shows the indicative site layout. The site layout has not been finalised at the time of this report.

For ease of reference, the trial pits were numbered according to their location thus: TPT1 refer to turbine 1; TPT2 refer to turbine 2, etc. For turbines with additional trial pits the turbine is followed by a suffix i.e. TPT1(1), TPT1(2). TPAT series refer to road/ track trial pits TPMM refers to the met mast area TPBP refer to the borrow pits followed by the associated borrow pit letter and followed by a suffix i.e.

TPBPd(1). Trial Pit photos are labelled by trial pit followed by a letter for each photo presented in the appendix i.e. TPT1a,

TPT1b, etc. Bulk samples were retrieved from selected trial pits and are stored at Natural Power’s offices and remain available for laboratory testing.

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Appendices

A. Trial Pit Photos

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WTG2

Figure 1: TPT2a Figure 2: TPT2b

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WTG3


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WTG4

Figure 5: TPT4a

Figure 6: TPT4b

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WTG6

Figure 7: TPT6a

Figure 8: TPT6b

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WTG7


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WTG8

Figure 11: TPT8a

Figure 12: TPT8b

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WTG9


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WTG12

Figure 15: TPT12a

Figure 16: TPT12b

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WTG13

Figure 17: TPT13a

Figure 18: TPT13b

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WTG14

Figure 19: TPT14a

Figure 20: TPT14b

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WTG16


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WTG17

Figure 23: TPT17a

Figure 24: TPT17b

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WTG18

Figure 25: TPT18a

Figure 26: TPT18b

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WTG19(1)

Figure 27: TPT19(1)a

Figure 28: TPT19(1)b

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WTG19(2)

Figure 29: TPT19(2)a Figure 30: TPT19(2)b

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WTG20

Figure 31: TPT20a

Figure 32: TPT20b

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WTG21

Figure 33: TPT21a

Figure 34: TPT21b

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WTG22


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WTG23


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WTG24

Figure 39: TPT24a

Figure 40: TPT24b

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WTG25

Figure 41: TPT25a

Figure 42: TPT25b

appendix 11a peat probing results - stornoway...

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