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Galloper Wind Farm Eastern Super Grid Transformer Project

Environmental Statement – Chapter 8 Geology, Hydrogeology, Land Quality, and Flood Risk

February 2014 Document Reference – GWF 20/02/2014

Galloper Wind Farm Limited

Galloper Wind Farm Eastern Super Grid Transformer Project Environmental Statement – Chapter 8 Geology, Hydrogeology, Flood Risk and Land Quality Final February 2014

CONTENTS Page 8 GROUND CONDITIONS 8.1 Introductions 1

8.2 Guidance and Consultation 1 8.3 Baseline 2 8.4 Assessment of impacts – worst case definition 7

8.5 Assessment of impacts during construction 7 8.6 Assessment of impacts during operation 9 8.7 Assessment of impacts during decommissioning 9 8.8 Inter-relationships 10 8.9 Cumulative Impacts 10 8.10 Monitoring 10 8.11 Summary 10 8.12 References 11 Figures Figure 8.1 Contaminated land baseline data coverage 4


8 GROUND CONDITIONS

8.1 Introduction

8.1.1 This chapter of the Environmental Statement (ES) examines the geology, hydrogeology, land quality, hydrology, and flood risk impacts associated with the construction, operation, and decommissioning phases of the proposed Eastern Super Grid Transformer (ESGT) which will be located within the Galloper Wind Farm (GWF) onshore site.

8.1.2 This chapter considers the potential impacts of the proposed development to the existing geological resource, upon hydrogeological (groundwater) sources (i.e. known aquifers), local watercourses (hydrology), land quality (the potential for contaminated land being present and / or the mobilisation of potential contaminants) and the generation of waste material. In addition the findings of a standalone Flood Risk Assessment (FRA) undertaken for the GWF onshore site are presented in chapter where they are relevant to the proposed ESGT.

8.1.3 The onshore development footprint of the proposed ESGT is located within the GWF onshore site (as shown in Figure 1.3).

8.1.4 Potential impacts associated with geology, hydrogeology, land quality and flood risk are not expected to occur beyond 1km of the proposed development due to the compact nature of the ESGT compound (other than offsite flood/drainage flow impacts that were considered in the FRA undertaken for the GWF ES). As such, the study area includes the onshore development footprint and any adjacent areas within 1km.

8.1.5 The GWF ES assessed the impact significance for land quality and water resources for the GWF onshore footprint and considered impacts on potential receptors within a 1km radius. The assessment undertaken for the GWF ES can be found in Appendix 1 of this ES. This assessment is revisited in this chapter to assess the impacts of the proposed ESGT and the consequent changes to the GWF onshore site.

8.2 Guidance and Consultation

8.2.1 GWF submitted a Scoping Report for the ESGT to Suffolk Coastal District Council in November 2013 and a Scoping Opinion was received in response in January 2014 (SCDC 2014). The Scoping Opinion contained a number of comments relating to Ground Conditions which are shown in Table 8.1, along with a description of where in this ES the comments have been addressed.

Table 8.1 Summary of Scoping Opinion Comments Date Consultee Summary of Comments Section of ES

where comment is addressed

13/12/2013 Suffolk County Council

Approach to EIA “We note the proposed updates to the information relating to noise,

This ES chapter provides an update to the


transport, terrestrial ecology, flood risk and archaeology. These will be important to verify the reduced impact of the ESGT compared to the full works consented by the Order…” –

transport assessment for GWF, taking into account the changes arising from the ESGT.

8.3 Baseline

Geology, hydrology, hydrogeology and land quality

8.3.1 A Phase I land quality investigation (desk study and site walkover survey) was undertaken in 2007 (Royal Haskoning, 2007) to acquire information for the design of, and to support, the planning application and Environmental Impact Assessment for the onshore substation and cable route of the Greater Gabbard Offshore Wind Farm (GGOWF) (Figure 8.1). A Phase II intrusive investigation was then undertaken following submission of the Environmental Statement for the GGOWF (Royal Haskoning, 2008).

8.3.2 The Phase I study area included the area of the proposed ESGT. The Phase II study area was limited to the substation and cable corridor footprint for GGOWF. However, given that this was on adjacent land it is considered that the Land Quality risks for ESGT are suitably categorised by these previous investigations.

8.3.3 A review of the GGOWF Phase I and Phase II land quality investigations has been undertaken to assess the environmental baselines for the ESGT, characterise the existing environment and to enable an assessment of the sensitivity of the various receptors.

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@A Borehole LocationExtent of 2007 Phase I ContaminatedLand Desk StudyExtent of 2007 Phase II Contaminated Land Intrusive SurveyEastern SGT redline boundaryGWF consented order limitsGreater Gabbard substation

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Coordinate System: British National GridMap Datum: OSGB1936Background data: Reproduced from Ordnance Survey digital map data© Crown copyright, All rights reserved. 2013.

Licence number 0100031673

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Land Use

8.3.4 The proposed ESGT will be located on the eastern edge of Sizewell Wents woodland. The western side of the compound will occupy an area of immature woodland, and the eastern side will occupy and area of pasture grassland. The ESGT will sit on an area of land that is between approximately 7m and 9m AOD.

Geology

8.3.5 The geology underlying the area is illustrated on the British Geological Survey (BGS) solid and drift geology map of the area (Sheet 191 Saxmundham) and is characterised by the Pleistocene Crag Group, which comprises undivided (Norwich) Crag, Chillesford Clay and, potentially, Red Crag in parts. A schematic of the solid geological formations from the surface down to bedrock is presented in Table 8.2.

Table 8.2 Summary of solid geological formations and hydrogeological properties Geological Unit Hydrogeological

Properties Approximate depth metres below ordnance datum (OD)

Ground surface

Pleistocene Crag Group (yellow or red/brown beds of sand, laminated clays and pebbly gravels) Secondary aquifer 0-50

Harwich Formation (siltstones and sandy mudstones, with volcanic ash layers) Non-aquifer

50-100 Hales Clay Member (sandy mudstones) Non-aquifer

Lambeth Group (mottled mudstones giving way to sands and silts) Non-aquifer

Ormesby Clay Formation (mudstones) Non-aquifer

Upper Chalk Principal aquifer 100-350

8.3.6 Within the study area there are no Regionally Important Geological Sites, no sites listed within the Geological Conservation Review nor any Sites of Special Scientific Interest designated for geological interest. Therefore, the study area is considered to be of low sensitivity for geology.

Hydrogeology 8.3.7 The study area is underlain by a number of hydrostratigraphic units comprising Crag

Deposits (secondary aquifer), London Clay, Lower London Tertiaries (non-aquifer), and Chalk (principal aquifer). The London Clay and the majority of the Lower London Tertiary units are non-aquifers which effectively act as an aquitard (impermeable layer along an aquifer). Table 8.2 shows a schematic of the hydrogeological formations.

8.3.8 The chalk aquifer which underlies the site is a principal aquifer whereas the overlying

crag deposits are indicated to be a secondary aquifer. These aquifers would not


normally warrant special consideration for Catchment Abstraction Management Strategy (CAMS) but may still support locally important abstractions and dependent ecosystems which may be subject to risks associated with pollution pressures. The site, however, does not sit within a Source Protection Zone (SPZ), the nearest being over 1km further to the west at Leiston which is ‘up gradient’ of the development site boundary, therefore there can be no hydrological movement from the development to this SPZ.

8.3.9 Although the site is underlain with both Principal and Secondary aquifers, the Principal aquifer is 100m below ground level with London Clay above it (acting as an aquitard). As such, the Secondary Aquifer is of more relevance to the proposed GWF and the site is therefore assessed as medium sensitivity for hydrogeology.

Encountered groundwater conditions 8.3.10 Groundwater monitoring wells were installed in the study area as part of the GGOWF

development, to provide information on groundwater levels and quality within the shallow aquifer beneath the site. Assessment of these levels show that the overall groundwater flow is approximately in a north-easterly direction, towards a series of drainage channels flowing north-eastwards into Sizewell Belts.

8.3.11 There is one licenced groundwater abstraction held within 500m of the site, which is for crop irrigation and is not considered to be a sensitive receptor. No water abstractions are proposed as part of the ESGT development.

8.3.12 Considering the classification of the underlying area as a secondary aquifer, and that groundwater has been identified beneath the site, the hydrogeology is considered to be of medium sensitivity.

Hydrology 8.3.13 The ESGT footprint does not include any surface water bodies and drains via surface

infiltration. A number of drainage channels run through Sizewell Belts to the north of the site, the nearest of which passes approximately 150m north of the ESGT boundary. The drains of the Sizewell Belts area discharge into Leiston Brook (approximately 1.7km north of the development boundary). Leiston Brook is a tributary of the Minsmere River which outfalls at Minsmere sluice approximately 3.35km north of the development site boundary.

8.3.14 The nearest water bodies to the site include a ponded hollow located approximately 50m to the south of Sizewell Wents. This surface water feature appears to be a temporarily flooded area of an arable field, rather than an established pond.

8.3.15 There are no sensitive surface water features within the development site. However, the network of drains 100m to the north of the ESGT site feeds into Sizewell Belts, a SSSI, although there is no direct surface water connectivity between these drains and the ESGT site. Therefore, the hydrology in the study area is considered to be of medium sensitivity.

Land Quality 8.3.16 No significant pollutant linkages were identified during the Phase II GGOWF

investigations and as such the sensitivity of the site to potential land quality impacts is considered to be low.


Flood Risk 8.3.17 The proposed ESGT is located in Flood Zone 1 which is defined as having a less than

0.1% chance of river or sea flooding. A Flood Risk Assessment (FRA) was undertaken for the GWF onshore site and is included in the GWF ES which is provided in Appendix 1.1. The risk of flooding in the area is considered to be low.

8.4 Assessment of impacts – worst case definition

8.4.1 The finished floor level of the ESGT is expected to be approximately 8.1m AOD. The GWF ES assumed the finished floor level of the GWF compound and transmission compound to be 8m, which is the worst case from a flood risk perspective.

8.5 Assessment of impacts during construction

Impacts to local geology 8.5.1 Excavation activities associated with the ESGT include surface excavation and earth

moving during site preparation. The foundations for the ESGT could be up to 4m deep. These excavations have the potential to disturb the local geology. However, as no sensitive geological features have been identified in the ESGT area, there is expected to be no impact upon the local geology. No mitigation measures are considered necessary.

Contamination of secondary aquifer (hydrogeology) 8.5.2 There is the potential for contamination from accidental leaks and spills from

construction vehicles used for construction of the ESGT and fuel storage onto the ground surface that could penetrate into the underlying strata. Secondary aquifers are of medium sensitivity and a potential minor adverse impact is predicted in the absence of mitigation.

Contamination of principal aquifer (hydrogeology)

8.5.3 The ESGT location is underlain by principal aquifer systems (Upper Chalk) which is overlain by London Clay which acts as an aquitard. None of the excavations or piling activity required for the ESGT will extend beyond the thickness of the London Clay (approximately 100m) and expose the chalk aquifer beneath to any potential contaminants. Therefore, no impact is predicted on the major aquifer during the ESGT construction.

Pollution of hydrological receptors (hydrology) 8.5.4 Excavations are likely to increase localised soil erosion and mobilised sediment can,

under certain circumstances, make its way into nearby watercourses through surface runoff. Depending on the scale of the excavation works, mobilised sediment can have serious adverse effects on the geomorphological and ecological functioning of a receiving watercourse and, as such, watercourses are afforded protection from silt run-off under Section.85 of the Water Resources Act 1991.

8.5.5 There are no surface water features within the ESGT site. The nearest sensitive watercourse is 100m from the site (a drain within Sizewell Marshes SSSI). Sizewell Marshes represents a hydrological receptor of medium sensitivity.


8.5.6 The increased risk of contaminated run-off entering Sizewell Marshes SSSI is limited, but due to the sensitivity of the watercourse, there remains the potential for an impact of minor adverse significance in the absence of mitigation.

Risk to site worker health (land quality) 8.5.7 Digging through potentially contaminated soil or waste materials (e.g. made ground)

could impact upon site worker health via dermal (direct) contact, ingestion or inhalation of soil, dust and/or any ground gases. Site workers would be in close or direct contact with contaminants, if present. However, the human health risk assessment which was undertaken as part of the Land Quality Assessment for GWF (see appendix 22C in the GWF ES) indicates a low risk from contamination if appropriate Personal Protective Equipment is used as a result of a risk assessment, and as such the impact prior to any mitigation measures is assessed to be negligible.

Mobilisation of contaminants (land quality / hydrogeology) 8.5.8 The ESGT construction will involve top soil stripping, earthmoving, excavations, and

foundation laying. These activities may enable greater percolation of rainfall across the working area and the mobilisation of contaminants, if present. However, no significant potential contamination sources have been identified therefore the impact is assessed to be negligible.

Generation of waste materials 8.5.9 The ground levels of the ESGT compound have been designed to minimise the amount

of cut and fill required, and to minimise the need for import or export of materials. Due to the intention to reuse excavated materials, the impact of waste generated from the scheme is considered to be negligible.

Increased risk of flooding 8.5.10 The proposed ESGT area is within Flood Zone 1 where the chance of sea or river

flooding is less than 0.1%. Therefore the risk of flooding during construction is considered to be negligible.

Mitigation measures and residual impacts 8.5.11 A Construction Code of Practice (CCOP) has been developed for the GWF onshore site

and it is expected that the measures within this will be applied to the ESGT construction. The CCOP contains the following measures:

• Minimisation of length of time that excavations are kept open

• Reinstatement of the excavated areas using appropriate fill materials if required

• Construction excavation, earthmoving and soil storage areas to be situated as far as possible from any surface water bodies

• All fuel storage will occur within bunded fuel tanks with a bund capacity of at least 110% of the tank volume. A minimum volume of fuel will be stored on site. The location of all fuel storage will be such that it minimises the risks to surface and groundwater

• All fuel and chemical storage will be located a minimum of 20m away from all watercourses


• An onsite briefing about the importance of the water supply, water bodies and use of pollution control packs will be disseminated to all site personnel

• Particular care will be taken when working with concrete as it is highly alkaline and can cause serious pollution to controlled waters;

8.5.12 If the mitigation measures above, and those listed in the CCOP (Appendix 3.1), the potential impacts on geology, hydrogeology, and ground conditions which are above negligible, will be reduced to negligible.

8.6 Assessment of Impacts during Operation

Geology and land quality 8.6.1 Operation of the ESGT is unlikely to have any impacts on geology or land quality

receptors as there will be no requirement for excavation or other ground disturbance. The potential impacts during operation are considered to be negligible.

Pollution of hydrological receptors 8.6.2 Surface water in the ESGT will drain via a soakaway. All surface water runoff from hard

standing areas within the ESGT will pass through an oil separator before being discharged into the soakaway to remove any hydrocarbon pollutants present in the runoff. Given the precautions in place, the potential impact is considered to be negligible.

8.6.3 The ESGT itself will stand within a concrete bund which will have underground oil containment, in case of leakage or full emergency oil discharge. This will ensure that oil leaks are fully contained and any oil can be taken offsite for appropriate disposal.

Flood risk and increase surface water runoff 8.6.4 The proposed ESGT will be located in Flood Zone 1 which has a less than 0.1% chance

of flooding from rivers or the sea. Therefore the risk of flooding during operation is considered to be negligible.

8.6.5 The proposed ESGT site is classified as greenfield. The ESGT will replace an area of grassland and woodland with some impervious surfaces, thus increasing the surface water runoff in that area. The new area of hardstanding which will be created is small compared to the surrounding land which is pervious.

8.6.6 The ESGT compound will cover an area of 0.83ha. The compound will contain areas of hardstanding such as the access road and the concrete bund beneath the SGT. Other areas of the compound will comprise pervious surfaces such as gravel chippings. The GWF onshore site is subject to a drainage strategy involving soakaways within the GWF substation compound and it is expected that the proposed drainage arrangement for the ESGT will complement this.

8.6.7 There are limited downstream receptors and the potential for increased flood risk due to increased surface water runoff is considered to be low. Therefore the risk of flood risk to downstream receptors is considered to be negligible.

8.7 Assessment of Impacts during Decommissioning

8.7.1 The decommissioning of the ESGT will be subject to the relevant legislation at the time. The impacts of decommissioning of the ESGT are considered to be equivalent to those


assessed for the construction phase. It is expected that the decommissioning will generate some waste material which is considered to have a minor adverse impact.

8.8 Inter-relationships

8.8.1 Inter-relationships which are considered relevant to geology, hydrogeology, land quality, and flood risk include those impacts on terrestrial ecology.

Terrestrial Ecology

8.8.2 In the absence of mitigation, there is the potential for accidental pollution incidents which could cause impacts on terrestrial ecology.

Mitigation and residual impacts

8.8.3 A CCOP (Appendix 3.1) has been developed for the GWF onshore site and it is expected that the measures set out in this will be applied to the ESGT site. The measures set out in the CCOP include those specifically designed to mitigate potential impacts to terrestrial ecology and land quality.

8.9 Cumulative Impacts

8.9.1 The proposed ESGT will be constructed instead of the consented Leiston B substation which was to be located within the Sizewell Wents woodland. The ESGT will form part of the GWF onshore site and the construction phases of the two will coincide.

Construction

8.9.2 The construction impacts of the GWF onshore site and the ESGT are largely the same, but will occur in slightly different areas. Both elements have the potential for contamination from leaks and spills, contaminated surface water, and erosion to effect the secondary aquifer, and hydrological receptors.

Operation 8.9.3 During operation, the proposed ESGT will be a direct replacement for the consented

Leiston B substation. Therefore although the ESGT will result in a new area of impervious surface, the effect of this will be more than compensated for by the fact that the Leiston B substation will not be constructed and a large area of the Sizewell Wents woodland will be retained.

Decommissioning

8.9.4 It is likely that the ESGT and the GWF onshore site will be decommissioned at the same time when the operational lifetime of GWF comes to an end. The potential impacts of decommissioning will be similar to those predicted for the construction phase.

8.10 Monitoring

8.10.1 No monitoring is proposed for geology, hydrogeology, land quality or flood risk.


8.11 Summary

8.11.1 Table 8.3 contains a summary of the impact assessment for hydrology, hydrogeology, and land quality.

Table 8.3 Summary of the impact assessment for hydrology, hydrogeology, and land quality Description of Impact Impact Mitigation Measure Residual Impact Construction Phase Impact to local geology No impact n/a n/a Contamination of secondary aquifer

Minor adverse The GWF CCOP will be applied to the ESGT construction

Negligible

Contamination of principal aquifer (hydrogeology)

No impact n/a n/a

Pollution of hydrological receptors (hydrology)

Minor adverse The GWF CCOP will be applied to the ESGT construction

Negligible

Risks to site workers health (land quality)

Negligible Negligible

Mobilisation of contaminants by rainfall (land quality)

Negligible Negligible

Generation of waste materials

Negligible n/a n/a

Increased flood risk Negligible n/a n/a Operation Phase Geology, hydrogeology and land quality

Negligible n/a n/a

Pollution of hydrological receptors (hydrology)

Negligible n/a n/a

Flood risk and increased surface water runoff

Negligible A drainage strategy will be implemented on the GWF site which the ESGT drainage will complement

Negligible

Decommissioning Phase As construction activities As above See construction

phase As above

Generation of waste Minor adverse Appropriate site waste management plan will be developed for decommissioning phase

Negligible

8.11.2 Once the proposed mitigation is applied, there will be no significant impacts during the

construction, operational, or decommissioning phase. The ESGT will directly replace the consented Leiston B substation and therefore will not lead to an increase in impervious surfaces compared to the consented GWF scheme.


8.12 References

Suffolk Coastal District Council 2014, Scoping Opinion for ESGT Project Royal Haskoning (2007). Contaminated Land Phase 1 Desk Based Assessment - Greater Gabbard Offshore Wind Farm Substation Site. Royal Haskoning (2008). Phase II Environmental Baseline Survey - Greater Gabbard Offshore Wind Farm Substation Site).

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