hinkley point c connection 400kv ohl – north and avonmouth

Card Geotechnics Limited Windsor House, Cornwall Road, Harrogate, HG1 2PW

Telephone: 01423 276000 www.cgl-uk.com

Balfour Beatty Power Transmission and Distribution (BBPT&D)

Hinkley Point C Connection 400kV OHL – North and

Avonmouth

Remediation Method Statement and

Piling Works Risk Assessment LD131

August, 2021

HI NKLEY POI NT C CO N NEC TIO N 4 00K V O HL - NOR TH A ND A VO NMOUT H Rem ediat ion Me thod Sta t ement and P i l ing Wo rks R isk Assessm ent

Card Geotechnics Limited, Windsor House, Cornwall Road, Harrogate, North Yorkshire, HG1 2PW Telephone: 01423 276 000

Copyright: Card Geotechnics Limited

Card Geotechnics Limited ("CGL") has prepared this report in accordance with the instructions of Balfour

Beatty Power Transmission and Distribution ("the Client") under the terms of its appointment for

consulting engineering services by the Client dated 28th March 2019. The report is for the sole and specific

use of the Client, and CGL shall not be responsible for any use of the report or its contents for any purpose

other than that for which it was prepared and provided. Should the Client require to pass copies of the

report to other parties for information, the whole of the report should be so copied, but no professional

liability or warranty shall be extended to other parties by CGL in this connection without the explicit

written agreement thereto by CGL.

Author Marina Kirkpatrick, Principal Engineer MSc BSc (Hons) CEnv MIEnvSc FGS

Checked Mark Stringer, Principal Engineer MSc BSc (Hons) PIEMA CGeol FGS

Approved Robin Slade, Regional Director BSc CEnv MIEMA

Reference CGN/04275K Revision 0 Issue Date August 2021


CGN/ 04 275 K 2

Contents

EXECUTIVE SUMMARY 3

1. INTRODUCTION 6

1.1 Proposed Development 7 1.2 Background and Objectives 7

2. SITE CONTEXT 9

2.1 General 9 2.2 Site Location and Description 9 2.3 Previous Desk Study and Ground Investigation 10

3. GROUND CONDITIONS 11

3.1 Geology 11 3.2 Groundwater 12 3.3 Hydrogeology and Hydrology 12

4. SUMMARY OF OHL TOWER CONSTRUCTION PROCESS 14

4.1 Overview 14 4.2 Mitigation Measures for the Protection of Controlled Waters 14 4.3 Stockpile Management 15 4.4 Waste Management 15

5. CONCEPTUAL SITE MODEL 17

5.1 Relevant Contaminant Linkages (RCL) 18

6. REMEDIATION OPTIONS APPRAISAL 20

6.1 Introduction 20 6.2 Remedial Options Appraisal 20 6.3 Preferred Remedial Options 22

7. REMEDIATION METHOD STATEMENT 23

7.1 Containment/Capping Layers 23 7.2 Concrete Design 24

8. WATCHING BRIEF 25

9. VERIFICATION 26

10. PILING WORKS RISK ASSESSMENT 27

10.1 Summary of Piling Options 27 10.2 Pollution Scenarios 28 10.3 Conclusions 31


CGN/ 04 275 K 3

FIGURES

Figure 1 Site Location Plan Figure 2 LD131 Tower Layout Plan and Post-Development Conceptual Site Model

APPENDICES

Appendix A Piling Sectional Profile Appendix B Remedial Options Appraisal Appendix C Backfill Import Specification (Chemical) Appendix D CGL Borehole Logs (LD130, LD131 & LD132)


CGN/ 04 275 K 4

EXECUTIVE SUMMARY

Card Geotechnics Limited (CGL) was commissioned by Balfour Beatty Power Transmission &

Distribution (BBPT&D) to produce Remediation Method Statements (RMS) and Piling Works Risk

Assessments (PWRA) for selected overhead line (OHL) towers on the new transmission line between

Hinkley and Seabank Power Stations (The Hinkley Point C Connection Project).

Following ground investigation and assessment it was established that RMS reports are required at OHL

Tower locations LD105, LD108, LD112, LD115, LD116, LD126, LD130, LD131, LD132. PWRA are also

required for OHL Tower locations LD105, LD108, LD115, LD116, LD126, LD130, LD131, LD132. This

report presents a site-specific RMS and PWRA for the tower at LD131 (the site).

The OHL tower at LD131 lies within the boundary of Crook’s Marsh Landfill Site, a former brick-pit that

is reported to have been infilled with a mixture of wastes including carbon black from the nearby

Sevalco site, excavation, demolition and construction waste, asbestos and radionuclides associated

with medical waste. Previous desk study has also highlighted a potential risk of encountering UXO in

superficial deposits during drilling and installation of piles.

Previous ground investigation by CGL at the LD131 tower location confirmed the presence of a 0.8m

thick layer of slightly sandy slightly gravelly clay described as Topsoil containing gravel of concrete, red

brick and mudstone. The Topsoil lay above Made Ground considered to represent landfill deposits

which was confirmed at LD131 to a depth of 10.7m bgl.

The Made Ground/landfill deposits were recorded to rest upon Tidal Flat Deposits described as soft

silty clay with occasional bands of sand to a depth of 17.7m bgl, below which gravelly silty clay, slightly

gravelly silty sand and gravel of the Mercia Mudstone Group were recorded between depths of

17.7m bgl and the termination depth of the borehole at 20.0m bgl. The ground investigation did not

confirm the presence of an existing landfill liner, or other form of protection against downward

migration of landfill leachate into underlying strata.

A groundwater strike recorded within Tidal Flat Deposits rose to rest at approximately the same

elevation as groundwater encountered within the landfilled materials (c.6m above Ordnance Datum)).

No leachability testing or groundwater sampling is known to have been completed at the site.

A summary of the site-specific conceptual site model (CSM) and refined risk assessment is replicated

from the previous CGL Contamination Assessment and Refined Risk Assessment. An options appraisal

is presented to assess potentially viable remediation techniques appropriate for identified

unacceptable contaminant linkages. The selected remediation measures are based on the


CGN/ 04 275 K 5

implementation of appropriate working practices to protect controlled waters, and removing the

pathway between source and receptor by completing construction works from a temporary working

platform above the level of the landfill. The pile caps will be formed within this temporary platform

and will remain above ground after its removal. This will eliminate the need to excavate into the

landfill material, for the protection of ground workers and to avoid generation of potentially hazardous

landfill waste. Together with the presence of the above ground pile caps, the recorded 0.8m thickness

of clay at ground surface, described as Topsoil, is considered to provide a suitable cover layer for the

protection of future users and will also to act to reduce infiltration for the protection of controlled

waters.

Potential risks to construction workers will be managed through appropriate health and safety

practices and risk assessments including the use of Personal and Respiratory Protective Equipment (PPE

and RPE). Due to the reported potential for radionuclides within the landfill waste, radiation

monitoring is recommended during groundworks, although previous monitoring has not recorded

radiation above background concentrations. Prevention and/or control of entry into confined spaces

to protect against potential exposure to ground gas and/or vapours is also required due to the

presence of landfilled materials.

A remediation method statement is presented together with requirements for a watching brief and

discovery strategy in the event of encountering unexpected contamination. A separate assessment of

potential risks associated with aggressive ground conditions has been completed by BBPT&D and this

has confirmed a buried concrete classification of AC2. A reassessment may be required where

foundations are placed within imported materials that have not undergone a concrete classification

assessment.

Based on the piling works risk assessment presented herein, the use of pre-cast concrete piles formed

within weathered sands of the Mercia Mudstone Group is considered unlikely to increase the risk of

contamination to controlled waters, future site users and construction workers. This assumes piles are

installed by a specialist piling contractor using a moulded pile with a tapered end to reduce the

potential for downward drag of contaminated soils and that the Secondary B Mercia Mudstone Group

aquifer is afforded some protection by the overlying cohesive Tidal Flat Deposits.

Piling contractors should be referred to the PWRA herein and to the CGL Ground Investigation Report

for details of the landfill materials and contamination migration potential in order for due care to be

incorporated into the piling methodology, including with respect to the potential for landfill gas,

radiation and UXO.


CGN/ 04 275 K 6

1. INTRODUCTION

Card Geotechnics Limited (CGL) has been commissioned by Balfour Beatty Power Transmission &

Distribution (BBPT&D) to produce Remediation Method Statements (RMS) and Piling Works Risk

Assessments (PWRA) for selected overhead line (OHL) towers along the new power transmission line

associated with the Hinkley Point C Connection Project.

To meet the requirements of the Environmental Statement1, BBPT&D prepared a Contaminated Land

and Groundwater Strategy2, on behalf of National Grid plc, for the North and Avonmouth Section of

the new OHL line between Hinkley Power Station and Seabank Power Station (Stage 10 of the

authorised development).

CGL produced a multi-site OHL Contamination Assessment and Refined Risk Assessment3 following

interpretation of chemical soil data obtained during pre-construction phases of ground investigation4.

This report is intended to support the BBPT&D Contaminated Land and Groundwater Strategy2 by

presenting remediation options and recommended methodologies to mitigate identified unacceptable

contamination risks during and after construction at OHL Tower LD131. A PWRA is also presented.

This report presents a summary of information collated from previous desk study5, ground

investigation4,6 and contamination assessment and refined risk assessment3. It is also intended to

address comments received by the client from the Environment Agency with respect to the proposed

piling works. The scope of remediation works and working practices to be implemented during piling

works, to mitigate identified unacceptable contamination risks to human health, construction workers,

controlled waters and buildings/structures, is also provided.

This report is subject to approval by the Environment Agency and Local Planning Authority(ies).

1 National Grid Environmental Statement Volume 5.9.1, Chapter 9 - Ground Environment. Hinkley Point C Connection Point

Regulation 5(2)(a) of the Infrastructure Planning (Applications: Prescribed Forms and Procedure) Regulations 2009. Application Reference EN020001, May 2014

2 National Grid document “Hinkley Point C Connection Project Stage 10.1 of the authorised development Requirement 18 – Contaminated Land and Groundwater Strategy”, Document 10.1 18 B CLG, November 2020

3 CGL “Contamination Assessment and Refined Risk Assessment” Hinkley Point C Connection 400kV OHL – North and Avonmouth, May 2021 (CGN04275J Rev 3)

4 Card Geotechnics Limited (CGL). Factual Ground Investigation Report. Hinkley Point C Connection 400kV OHL – North and Avonmouth October 2020. Ref. CGN/04275B/C

5 Mott MacDonald (2020) Hinkley OHL Contaminated Land Assessment. Ref 408878 – MMB-00-XX-RP-EN-ZZZZ-0022-Contaminated Land Report-P01. 28th February 2020

6 LSTC Group “SCHEME: Seabank 132kV Line Terminations Ground Investigation Report” LSTC Reference 21/18253/13, 2018


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1.1 Proposed Development

The Hinkley Point C Connection transmission line includes a section of overhead line that will form the

North and Avonmouth Section. This will run from OHL Tower LD40 north of Sandford to LD132 at the

Seabank Power Station in Avonmouth. The North Section (Towers LD40 to LD99) generally traverses

low lying agricultural land between the Mendips Hills Area of Outstanding Natural Beauty (AONB) and

Avonmouth. The Avonmouth section (LD100 to LD132) runs through Avonmouth Dock and the area

built-up around it, crossing the River Avon between Towers LD107 and LD108. The route terminates at

Tower LD132 adjacent to Seabank Power Station.

1.2 Background and Objectives

CGL produced a multi-site OHL contamination assessment and refined risk assessment3 following

interpretation of chemical soil data obtained during pre-construction phases of ground investigation4.

The results of the assessment confirmed that remedial action, to address unacceptable contamination

risks, is required at OHL Tower locations: LD105, LD108, LD112, LD115, LD116, LD126, LD130, LD131,

LD132. A requirement for PWRA was also identified for OHL Tower locations LD105, LD108, LD115,

LD116, LD126, LD130, LD131, LD132.

This RMS and PWRA report is intended to present a remediation strategy, based on an appraisal of

options, to address site-specific contamination identified at OHL Tower LD131, as identified in the CGL

contamination assessment and refined risk assessment3. It presents a selection of practicable, cost

effective and sustainable remediation solutions for implementation prior to and during construction.

Associated verification requirements are also presented in accordance with good practice7,8,9.

A watching brief and discovery strategy is also presented herein and should be maintained during

ground works in the event that unexpected contamination is encountered during construction.

This report also presents a summary of measures to be implemented in relation to drainage, pollution

incident control, waste and soil management. Further details with regards to these aspects are

provided in the following reports which should be consulted in full:

National Grid “Hinkley Point C Connection Project. Stage 10.1 of the Authorised

Development. Requirement 6(1) (A) – Soil Management Plan” Document 10.1 6A B SMP,

March 2021.

7 Environment Agency. (2010). Verification of remediation land contamination. Report SC030114/R1. 8 Environment Agency. (2010). Guiding Principles for Land Contamination Reports. March 2010. 9 https://www.gov.uk/government/publications/land-contamination-risk-management-lcrm


CGN/ 04 275 K 8


Development. Requirement 6(1) (B), 17, 19 and 21 – Drainage Management Plan” Document

10.1 6B B DMP, March 2021.


Development. Requirement 6(1) (C) - Pollution Incident Control Plan” Document 10.1 6C B

PICP, November 2020.


Development. Requirement 6(1) (G) – Site Waste Management Plan” Document HCP 10.1 6 1

(G) B SWMP, January 2021.


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2. SITE CONTEXT

2.1 General

This report should be read in conjunction with the following reports previously prepared to support the

BBPT&D Contaminated Land and Groundwater Strategy2:

Mott MacDonald (2020) Hinkley OHL Contaminated Land Assessment. Ref 408878 – MMB-00-

XX-RP-EN-ZZZZ-0022-Contaminated Land Report-P01. 28th February 2020;

Card Geotechnics Limited (CGL). Factual Ground Investigation Report. Hinkley Point C

Connection 400kV OHL – North and Avonmouth, November 2020. Ref. CGN/04275B/C; and,

Card Geotechnics Limited (CGL). Contamination Assessment and Refined Risk Assessment.

Hinkley Point C Connection 400kV OHL – North and Avonmouth, May 2021 (Rev 3) Ref:

CGN/04275J.

The following report also presents details of historical desk study and ground investigation completed

at the Crook’s Marsh Landfill Site (see further information below):

LSTC Group “SCHEME: Seabank 132kV Line Terminations Ground Investigation Report” LSTC

Reference 21/18253/13, 2018.

2.2 Site Location and Description

The site (LD131) is located approximately 300m south east of Seabank Power Station, approximately

5km north east of Avonmouth. Environment Agency (EA) records confirm the site lies within the

boundary of the “Authorised A01: Co-Disposal Landfill Site” at Crooks Marsh Farm Landfill Site (Ref:

EA/EPR/UP3999FL/A001) licence issued on 16/01/198610.

The Ordnance Survey grid reference for the centre of the site is 353913, 181922. The topography of

the general site area is roughly level at approximately 12m above Ordnance Datum (OD).

A site location plan for the wider scheme, including LD131, is presented as Figure 1. A tower layout

plan is included in Figure 2.

10

https://environment.data.gov.uk/DefraDataDownload/?mapService=EA/PermittedWasteSitesAuthorisedLandfillSiteBoundaries&Mode=spatial


CGN/ 04 275 K 10

2.3 Previous Desk Study and Ground Investigation

A ground investigation report by LSTC Group (LSTC) has been provided to CGL to support development

of this remediation method statement and piling works risk assessment11. This report summarises

previous desk study information12 which confirms the site lies within a former brick-pit which was

operated by Ibstone Bricks during the 1970s and 1980s. It was subsequently filled with waste generally

comprising carbon black residues from the nearby Sevalco site, used in the production of tyre rubber

from the 1950s to 2008. The landfill is reported to have accepted wastes including incinerator residues

from the Avonmouth Refuse Disposal works, excavation, demolition and construction waste, minor

quantities of asbestos and radionuclides, assumed to be associated with medical waste.

The landfill is referred to as Crook’s Marsh Landfill Site and is reported to have operated as such until

1996, after which time it was capped and procured by Bristol City Council11. Details of capping works

were not available at the time of the LSTC investigation, but it was understood the landfill was capped

with compacted reworked clays before being ‘remediated’ by the placement of 1-2 metres of thermally

dried sewage sludge and general rubble.

The ground investigation completed by LSTC Group confirmed the presence of up to 2m of soft

thermally dried sewage sludge with inherent low bearing capacity overlying landfilled material. The

landfill material was described as a heterogeneous mix of very soft to firm sandy gravelly silty clays

containing brick, limestone, ceramics, slate, wire, wood, charcoal and metal with pockets of black

plastic amorphous peat. Firm clay with roots and rootlets containing gravel of limestone and

mudstone; gravelly silty sand; very gravelly clay containing brick, limestone, metal, glass, timber and

plastic; and, gravel and cobbles of concrete, tarmac and metal were also recorded. The landfill material

was recorded to rest directly upon Tidal Flat Deposits and Mercia Mudstone Group from depths

between 6.5m bgl and 12.4m bgl.

Radionuclide monitoring was completed during the LSTC ground investigation using a Geiger Muller

Mini Series 900 Counter11. No radiation levels in excess of background open air conditions were

observed.

The LSTC report concludes, given the site’s use as a brick pit and subsequent landfill site, the risk of

encountering UXO at shallow depth is likely to be low; however, a potential risk of encountering UXO in

deeper natural superficial deposits during drilling and the installation of piles was identified.

11 LSTC Group “SCHEME: Seabank 132kV Line Terminations Ground Investigation Report” LSTC Reference 21/18253/13, 2018 12 Jacobs Scope for Ground Investigation Crooks Marsh dated 12/04/2018 – this report and a Wardell Armstrong report were

not available to CGL but these are referred to in the LSTC Group report


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3. GROUND CONDITIONS

3.1 Geology

The British Geological Survey (BGS)13 website indicates the site is underlain by superficial deposits

comprising Tidal Flat Deposits (clays and silts) overlying mudstone bedrock of the Mercia Mudstone

Group. No artificial deposits are recorded.

CGL undertook a ground investigation at LD131 in 20204 which confirmed the presence of a 0.8m thick

layer of slightly sandy slightly gravelly clay described as Topsoil (and possibly representing restoration

soils) containing gravel of concrete, red brick and mudstone. The recorded Topsoil lay above Made

Ground described as dark brown mottled black becoming reddish brown gravelly silty clay with gravel

of sandstone, mudstone, concrete and red brick and frequent fragments of pottery, timber, wood,

glass and metal wire recorded to a depth of 5.8m bgl. Below this, the Made Ground was described as

odorous sandy gravel of angular fine metal shards with frequent glass, plastic, wood, tin cans, bin bags

and wire and an increasing content of red brick and concrete to a depth of 10.2m bgl. These Made

Ground/landfill deposits were underlain by a 0.5m thick layer of soft slightly sandy silty clay. A strong

hydrocarbon odour was recorded between depths of 5.8m and 10.2m bgl.

The basal clay layer beneath the landfill deposits was considered at the time of the CGL investigation to

be a potential landfill liner; however, it was not recorded at the base of the nearby borehole at LD132

(which is also within the boundary of Crook’s Marsh Landfill Site) and so the potential liner identified at

LD131 is not considered to be a consistent feature at the base of the landfill deposits.

The Made Ground deposits were recorded to rest upon Tidal Flat Deposits described as soft silty clay

with occasional bands of sand to a depth of 17.7m bgl, below which firm slightly gravelly silty clay and

slightly gravelly silty sand of the Mercia Mudstone Group (Destructured Grade IVa) was recorded

between depths of 17.7m bgl and 19.3m bgl. Distinctly Weathered mudstones of the Mercia Mudstone

Group (Grade III) were recovered as gravel to the base of the borehole which was terminated at

20.0m bgl.

Throughout the CGL investigation, all arisings were screened with a Tracerco T407 radiation monitor

and no readings above background radiation levels were recorded.

13 http://mapapps2.bgs.ac.uk/geoindex/home.html


CGN/ 04 275 K 12

3.2 Groundwater

Two groundwater strikes were recorded during drilling at LD131: one within the landfill deposits at

5.9m bgl rising to 5.27m bgl and a second upon encountering the Tidal Flat Deposits at a depth of

10.7m bgl, rising to 5.96m bgl within 20 minutes. The borehole at LD131 was progressed using clean

drilling techniques, with a 2m thick bentonite seal placed at the base of the Made Ground deposits at a

depth of 10.7m bgl before drilling through this seal into the underlying Tidal Flat Deposits.

The borehole log indicates the second groundwater strike was encountered immediately upon

breaching the bentonite seal. This groundwater then rose to rest at approximately the same elevation

as the groundwater encountered within the landfilled materials (c.6mAOD), suggesting the deeper

groundwater strike was subject to the same hydraulic head as that within the landfilled material at the

time of drilling. This would suggest the groundwater strike within the Tidal Flat Deposits was confined

beneath the landfilled material prior to drilling .

The borehole logs for LD130, LD131 and LD132 are presented in Appendix D.

3.2.1 Previous CGL Contamination Assessment

During the previous CGL ground investigation4, three soil samples were collected from Made Ground at

depths of 0.5m, 1.0m and 2.0m bgl. Laboratory testing confirmed that concentrations of

contamination in these samples were below commercial generic assessment criteria (GAC).

Given the heterogeneous nature of the recorded landfilled materials and the extent of landfill deposits

below the sampled horizons, it is considered likely that unacceptable concentrations of contamination

may exist at depth beneath the site.

No leachability testing or groundwater sampling was completed because this was outside of the scope

of the specification for the CGL ground investigation.

3.3 Hydrogeology and Hydrology

The Environment Agency (EA) has produced an aquifer designation system consistent with the

requirements of the Water Framework Directive14 (WFD) which classifies the underlying soils as:

Tidal Flat Deposits - Unproductive Strata; and

Mercia Mudstone Group - Secondary B Aquifer.

14 EU Water Framework Directive (2000/60/EC)


CGN/ 04 275 K 13

The site is not located within a groundwater Source Protection Zone (SPZ).

The site is located in an area allocated as Flood Zone 3 within an area benefiting from flood defences15.

The nearest surface water feature is a drainage channel near the southern boundary which is

presumed to drain to the River Severn approximately 1.5 km west of the site via Stuppill Rhine.

15 https://flood-map-for-planning.service.gov.uk/

https://flood-map-for-planning.service.gov.uk/


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4. SUMMARY OF OHL TOWER CONSTRUCTION PROCESS

4.1 Overview

The overall construction works consist of the installation of a double circuit ‘northern section’ of the

400kV Overhead Line Route, with a route length of approximately 31.2km between Sandford

Substation to Seabank Power Station. The towers to be erected are OHL Towers LD40 to LD132: The

new T-Pylons will be installed for towers LD40-LD105; extended height lattice towers will be installed

for Towers LD107-LD108 and standard height lattice towers (L12) will be installed for Towers LD106

and LD109-LD132.

Prior to construction, enabling works for the piling operations at LD131 will entail installing a “floating”

road over the landfill site to OHL towers LD131 & LD132. Workpads for construction at these two

towers will be installed on top of the landfill so that excavation into the landfill is not required. The

piles will therefore be driven from a platform above the landfill. The floating platforms will be

excavated to the top of landfill material and the pile caps will be installed in this material, above the

landfill level. Following construction and installation of the conductors, the floating platforms and haul

roads will be removed leaving the pile caps above ground level.

Sectional profiles provided by BBPT&D detailing the depth of piling works are provided in Appendix A.

4.2 Mitigation Measures for the Protection of Controlled Waters

The Drainage Management Plan (DMP)16 and the Pollution Incident Control Plan (PICP)17 documents for

Stage 10 of the authorised development record the measures that will be employed during

construction to protect controlled water receptors and these should be referred to for further details.

It is assumed the following measures documented therein will be implemented to mitigate potential

risks to controlled waters (as reflected in the CGL refined risk assessment3):

Compliance with Environment Agency (EA) approved permits, consents and EA Regulatory

Position Statements;

Treatment and/or disposal of contaminated water and measures to ensure water discharged

to watercourses is not contaminated;

16 National Grid “Hinkley Point C Connection Project. Stage 10.1 of the Authorised Development. Requirement 6(1) (B), 17, 19

and 21 – Drainage Management Plan” Document 10.1 6B B DMP, March 2021 17 National Grid “Hinkley Point C Connection Project. Stage 10.1 of the Authorised Development. Requirement 6(1) (C) -

Pollution Incident Control Plan” Document 10.1 6C B PICP, November 2020


CGN/ 04 275 K 15

Daily inspection of watercourses, use of silt fencing and appropriate stockpile management in

accordance with the National Grid Soil Management Plan18;

Spill prevention and use of spill kits/absorbent material, plant nappies and/or drip trays; and,

Appropriate waste management procedures to ensure safe storage, transport and disposal of

waste, in accordance with the Site Waste Management Plan19.

4.3 Stockpile Management

Stockpiles will be managed in accordance with the National Grid Soil Management Plan (SMP)18 of

Stage 10.1 of the authorised development. The SMP describes methods for the storage and handling

of soils, topsoil and subsoil and the controls required in accordance with the Construction

Environmental Management Plan (CEMP20). It is assumed the measures documented will be

implemented to mitigate potential risks to controlled waters (as reflected in the CGL refined risk

assessment3).

The SMP specifies how stockpiles will be recorded and managed including measures for:

Segregation, handling, trafficking, tagging and auditing of soils;

Location, spacing, ground protection, fencing and exclusion zones;

Maximum heights, widths and lengths of stockpiles;

Stabilisation, drainage management, flood and erosion prevention measures including in the

event of heavy rainfall/wind/frost/drought, etc.; and,

Reinstatement and re-seeding requirements.

4.4 Waste Management

Waste will be managed in accordance with the National Grid Site Waste Management Plan (SWMP)19 of

Stage 10.1 of the authorised development which presents procedures for the storage, transfer, re-use,

recycling and disposal of waste.

18 National Grid “Hinkley Point C Connection Project. Stage 10.1 of the Authorised Development. Requirement 6(1) (A) – Soil

Management Plan” Document 10.1 6A B SMP, March 2021 19 National Grid “Hinkley Point C Connection Project. Stage 10.1 of the Authorised Development. Requirement 6(1) (G) – Site

Waste Management Plan” Document HCP 10.1 6 1 (G) B SWMP, January 2021 20 National Grid “Environmental Statement. Construction Environmental Management Plan” Document 5.26.1C


CGN/ 04 275 K 16

The objectives of the SWMP are to meet the aim of targeting “Zero Waste” to landfill for the Hinkley

project and to apply the Waste Hierarchy in accordance with the Waste Regulations (2011)21 to:

Minimise raw materials consumed, and the volume of waste produced including ‘designing

out waste’ and waste prevention measures;

Re-use any waste produced, where practicable;

Recycle waste, where reuse is not practicable;

Recover waste, where feasible; and

Dispose of any remaining waste streams in accordance with legislative requirements.

The generation of waste soils will be avoided at LD131 due to the installation of a floating working

platform above the level of the landfill. Excavation is required into the temporary working platform to

make way for the pile caps and it is assumed removal of this will be managed with the material

removed from the temporary working platform and haul road in accordance with the SMP18.

All waste will be managed in accordance with the SWMP19. Waste soil will be classified as Hazardous /

Non-Hazardous in accordance with WM322 and in accordance with the Landfill (England and Wales)

Regulations 2002 (as amended), to ensure recovery or disposal at an appropriately permitted facility.

All material intended for off-site disposal will be transported and disposed in accordance with the

Environmental Protection (Duty of Care) Regulations, 1991 and the Landfill (England and Wales)

Regulations, 2002 (as amended).

21 The Waste (England and Wales) Regulations 2011 22 EA, Technical Guidance WM3: Waste Classification - Guidance on the classification and assessment of waste, April 2014


CGN/ 04 275 K 17

5. CONCEPTUAL SITE MODEL

A summary of the site-specific conceptual site model (CSM) and refined risk assessment3 for OHL Tower

LD131 is summarised below in Table 1. The risk assessment process has been undertaken in line with

the UK Government Land Contamination Risk Management (LCRM) guidance23 and the results are

replicated in Table 1 from the CGL Contamination Assessment and Refined Risk Assessment report3.

Table 1 Summary of Site-Specific Conceptual Site Model and Refined Risk Assessment – LD131 Source/Medium Receptor Potential Exposure Route Risk Rating3

On-site Sources MADE GROUND: Residual contamination from on and off-site historical land use – i.e. agriculture and general site development, Philblack Works and brick works. Crooks Marsh Farm Co-Disposal Landfill Site. Made Ground thickness: 10.7m (0.8m Topsoil overlying 9.4m of landfilled waste). Visual and Olfactory Contamination: Landfill materials – Made Ground 0.8m to 10.2m bgl containing concrete, red brick, plastic, metal, wood, timber, pottery, wire, glass, tin cans, and plastic bags. A strong hydrocarbon odour between depths of 5.8m and 10.2m bgl. Confirmed contaminants of concern during CGL Ground Investigation: None above CGL Commercial Generic Assessment Criteria. Residual contamination from historical records of deposited landfill

materials in Crook’s Marsh Landfill6: • Thermally dried sewage sludge

and wet sewage sludge. • General demolition rubbish. • Possible asbestos. • Black carbon residues (from

tyre production). • Incinerator residues. • Radionuclides (medical waste). • Potential heavy metals.

Human Health Construction workers

Direct ingestion of soil & dust, inhalation of particulates & vapours and dermal contact. Inhalation of airborne asbestos fibres

Moderate/Low

Human Health End Users Direct ingestion of soil & dust, inhalation of particulates & vapours and dermal contact. Inhalation of airborne asbestos fibres

Moderate/Low

Groundwater - Secondary B Aquifer

Leaching from soils and migration off-site in groundwater

Moderate/Low

Surface water Base flow and surface run-off/drainage to surface water

Moderate/Low

Aggressive Ground Conditions Concrete & structures Direct contact and chemical attack Low - BBPT&D assessment indicates concrete classification AC-2.

23 https://www.gov.uk/government/publications/land-contamination-risk-management-lcrm

https://www.gov.uk/government/publications/land-contamination-risk-management-lcrm


CGN/ 04 275 K 18

The potential risk to construction workers from contamination at the site relates predominantly to

short-term (acute) exposure. Short-term construction risks will be mitigated through the

implementation of appropriate health and safety working practices required on UK construction sites in

accordance with Health and Safety Executive legislation and guidance. This includes site (and

contamination) specific risk assessments prepared by the Contractor and use of appropriate personal

protective equipment (PPE) and respiratory protective equipment (RPE), as necessary.

Appropriate working practices and construction methods will also mitigate potential risks to off-site

receptors during construction, through nuisance control for noise, odour and off-site dust migration for

example. As part of this process, stockpiled material or excavations should be dampened down and,

where possible, covered during all earth moving activities.

Should suspected asbestos containing materials (ACMs) be encountered in excavations they should be

dampened, isolated, double bagged and either sent for analysis before disposal or disposed of as

Hazardous Waste. Disposal of ACMs should be undertaken by an appropriately licensed contractor,

experienced in the identification of asbestos, in accordance with current regulations24,25 and guidance26

under controlled conditions.

Mitigation measures to address potential risks to vegetation and plants were also considered as part of

the risk assessment process3. The OHL tower at LD131 lies within a landfill site with a scrub grassland

ground cover. As such, potential risk to vegetation from the OHL tower development is not considered

to be relevant to this site.

5.1 Relevant Contaminant Linkages (RCL)

Relevant Contaminant Linkages (RCLs) to be considered under a remediation options appraisal are

those assessed as ‘moderate/low’ risk or higher in Table 1. The risk to concrete and structures has

been assessed separately by BBPT&D and further details are provided in Section 7.2.

A summary of the RCLs to be considered in an options appraisal are summarised below in Table 2.

24 Health and Safety Executive (2012) The Control of Asbestos Regulations 25 CL:AIRE (2016), Control of Asbestos Regulation 2012, Interpretation for Managing and Working with Asbestos in Soil and

Construction and Demolition Materials: Industry guidance. 26 HSG247 (2012) Asbestos: The licensed contractors’ guide


CGN/ 04 275 K 19

Table 2. Relevant Contaminant Linkages (RCLs) Contaminant Linkage

Source Pathway Receptor(s)

RCL1 Made Ground: Landfill materials Direct (oral and dermal) exposure

Construction workers Future site occupants

RCL2 Made Ground: Landfill materials Inhalation of dust/asbestos fibres

Future site users Construction workers

RCL3 Made Ground: Landfill materials Radiation exposure Future site users Construction workers

RCL4 Made Ground: Landfill materials Leaching and migration off-site in groundwater

Groundwater

RCL5 Made Ground: Landfill materials Migration in drainage channels and groundwater

Surface Waters

Potential short-term (acute) risk to construction workers will be mitigated through the implementation

of working practices usual on UK construction sites including site (and contamination) specific risk

assessments and use of appropriate PPE/RPE. Due to the potential for radionuclides within the landfill

waste, radiation monitoring is recommended during groundworks, although records of radiation

monitoring during the previous LSTC and CGL ground investigations did not record levels of radiation

above background concentrations6,4.


CGN/ 04 275 K 20

6. REMEDIATION OPTIONS APPRAISAL

6.1 Introduction

A remedial options appraisal is required to assess the viability, cost effectiveness and sustainability of a

range of remedial options for treatment, recovery and/or disposal of contaminated soils at the site.

According to the principles of risk assessment, remedial approaches for the mitigation of identified

contaminant linkages include:

Addressing the source by either removal or treatment;

Breaking the linkage between the source and receptor by using some form of pathway

interception or containment system; and/or

Protection of the receptor either through institutional control or control of future

redevelopment.

Potential pollution scenarios and associated risks during the proposed piling operations are assessed

separately under the PWRA in Section 10.

6.2 Remedial Options Appraisal

The RCLs to be considered under a remediation options appraisal are listed in Table 2 and relate to the

following source:

Made Ground: Landfill materials.

Potential risks relate to human exposure during construction and future human exposure where Made

Ground remains at ground surface following construction due to direct and indirect exposure pathways

as well as leaching to groundwater and migration into surface water receptors.

The applicability of potential remedial options for addressing potential contamination at the site is

considered in a remedial options appraisal in Appendix B. A general discussion is given with respect to

the viability of applicable remedial techniques in accordance with the LCRM Remediation Option

Applicability Matrix27.

Potential risk to surface waters and groundwater is considered to be mitigated by the implementation

of working procedures and incident response action plans in accordance with the Drainage, Pollution

27 Land contamination: remediation option applicability matrix - GOV.UK (www.gov.uk), Version 1, 24 May 2019

https://www.gov.uk/government/publications/land-contamination-remediation-option-applicability-matrix


CGN/ 04 275 K 21

Incident Control, Soil and Waste Management reports for stage 10.1 of the authorised development.

Summary details are provided in Section 4.2, Section 4.3 and Section 4.4.

On this basis, the preferred remedial options to address the RCLs at LD131 are:

Construction design to eliminate the need to excavate into the source; and,

Use of a containment / cover system.

The construction design at LD131 excludes excavation into the landfilled material for the protection of

groundworkers. Instead, during the construction of OHL towers LD131 & LD132, a floating road and

working platform will be installed on top of the landfill so that excavation into the landfill material is

not required. Pre-cast concrete piles will be driven from the surface of the temporary platform which

will then be excavated to the original surface of the landfill to create space for the installation of the

pile caps which will be cast in-situ. Following construction, the floating platforms and haul roads will be

removed leaving the pile caps above ground level.

Records suggest the Crook’s Marsh landfill site has been capped with thermally dried sewage sludge

and general rubble6. The CGL borehole at LD131 did confirm the presence of an approximately 0.8m

thick surface cover, described as Topsoil, that did not contain the visible waste materials evident below

that depth (e.g. plastic, metal, wire, wood, timber, wire etc).

Soil sampling did not indicate the presence of significant concentrations of contamination in the three

soil samples collected from the upper 2.0m bgl of Topsoil and landfilled material3. Based on this

testing, and when considered together with the presence of the above ground pile caps, the Topsoil

material is considered likely to provide a suitable cover layer for the protection of future users of the

site, who are expected to be land owners and maintenance staff who are aware of the site condition as

a landfill. The cover layer will have remained in-situ during construction because the temporary

working platform will be constructed on top of it to avoid excavation.

The selected remedial approach is based on breaking the contaminant linkage between source and

receptor by reducing potential direct exposure to landfill materials and also reducing infiltration for the

protection of controlled waters. It is expected that potential short term acute risk of exposure under

future use will also be managed through appropriate working practices, risk assessment, radiation

monitoring and appropriate use of PPE and RPE.

The construction design will also reduce disturbance of the landfilled waste which could mobilise

contaminants within the landfill and impact upon groundwater and surface water receptors.

Procedures to be followed within the Stage 10.1 Drainage, Pollution Incident Control, Soil and Waste


CGN/ 04 275 K 22

Management Plans16,17,18,19 will mitigate potential risk of pollution to controlled waters during

construction and the presence of the in-situ Topsoil layer will act to reduce downward infiltration of

rainwater.

The chosen method of piling (driven pre-cast concrete) is considered unlikely to increase the risk of

downward contaminant migration because this piling method is expected to reduce the permeability of

soils in direct contact with the pile. In addition, the use of a tapered end will reduce the potential for

downward drag of contamination as piling proceeds. Further details and presentation of a piling works

risk assessment is given in Section 10.

6.3 Preferred Remedial Options

The preferred remedial measures with respect to the identified RCLs are summarised in Table 3 below:

Table 3. RCL Specific Works Contaminant Linkage Remedial Objective Remedial Action

RCL 1-2

To mitigate the potential risk by breaking the linkage between source and receptor by pathway interception.

Eliminate the need to excavate into landfill material. Cover system overlying landfill materials – already in-situ above the landfill.

RCL 3 To protect construction workers from potential radiation exposure through elimination of source and real-time monitoring at source.

Eliminate the need to excavate into landfill material. Radiation monitoring during groundworks.

To protect future site users from potential radiation exposure.

Cover system overlying landfill materials – already in-situ above the landfill to remove potential exposure pathway to future users.

RCL 4 and 5 To mitigate the potential risk by breaking the linkage between source and receptor by pathway interception. Working methods, procedures and responses to pollution incidents. Reduce vertical migration and dragging down of contaminants.

Cover system overlying landfill materials – already in-situ above the landfill. To reduce infiltration and potential downward migration of soluble contaminants to the Secondary B Aquifer. Implementation of the Stage 10.1 Drainage, Pollution Incident Control, Soil, and Waste Management Plans during construction. Use of driven, pre-cast concrete piles with tapered end.


CGN/ 04 275 K 23

7. REMEDIATION METHOD STATEMENT

Based on the site-specific conceptual site model, refined risk assessment and options appraisal, the

proposed remediation strategy to address the RCLs comprises:

Elimination of the need to excavate into the landfill material (source removal);

Implementation of working procedures in accordance with the Draining, Pollution Incident

Control, Soil, and Waste Management Plans (refer Section 4.2, Section 4.3 and Section 4.4 for

summary details)

Re-use of the existing Topsoil (clay) surface cover layer to remove potential direct exposure

pathways and to reduce infiltration and mobilisation of contaminants to controlled waters;

Potential future (short-term) exposure to be managed through radiation monitoring and

appropriate working practices and risk assessment with appropriate use of PPE and RPE; and,

Provision of suitable concrete mix to mitigate against potential soil aggressivity.

7.1 Containment/Capping Layers

Due to the presence of landfill materials a capping layer is required to prevent direct contact by future

end users. The re-use of the existing Topsoil cover layer, together with the above ground pile caps, is

expected to provide this protection. The Topsoil material will remain in-situ during the tower

construction and therefore no further works are required.

The presence of the current clay cover layer above the landfill material will reduce infiltration of

rainwater, and therefore the retention of current conditions together with the presence of

approximately 7m of cohesive Tidal Flat Deposits will act to reduce vertical migration to the underling

Secondary B Aquifer.

Where soil is required to be imported on to the site for the purposes of reinstatement or backfill, it

should meet the chemical requirements stated in Appendix C. These import criteria are conservatively

based on GAC for a residential without plant uptake end use to ensure the quality of imported soils

provides an improvement to current conditions. Chemical data should be obtained from the provider

prior to importing it to site to confirm it is chemically acceptable for use as well as evidence the

material meets “end of waste” requirements as appropriate.

Additional consideration of the potential risk to controlled waters during piling is presented in Section

10 below.


CGN/ 04 275 K 24

7.2 Concrete Design

An assessment has been completed by BBPT&D in accordance with BRE Special Digest 1 report28. The

concrete classification reported to be appropriate for the site is AC-2. A reassessment may be required

where foundations are placed within imported materials that have not undergone a concrete

classification assessment.

28 Building Research Establishment. (2005). Concrete in aggressive ground, Special Digest 1


CGN/ 04 275 K 25

8. WATCHING BRIEF

The design of the construction process has eliminated the need to excavate into the landfill materials

and it is therefore unlikely that unexpected contamination will be encountered. The use of pre-cast

concrete piles will also mean there is no production of waste pile arisings.

However, should unexpected contamination become apparent, a watching brief should be undertaken

and the Discovery Strategy outlined below should be followed. This is to avoid introducing additional

contamination linkages and to minimise and appropriately manage waste through careful segregation

and storage of excavated soil and pile arisings. The aim is that volumes of waste soils are minimised

and mixing of wastes is avoided. Stockpiles should be segregated into topsoil, subsoil, materials from

Made Ground and natural soils as well as potentially Hazardous and Non-Hazardous materials.

Where unexpected gross contamination, such as oily material or material of an unusual colour or

odour, is encountered, the following discovery strategy is recommended:

1. Works to cease in that area.

2. Notify geoenvironmental engineer, to attend site and sample material for appropriate analysis

and risk assessment.

3. Notify Contaminated Land Officers of the Local Authority and Environment Agency, as

appropriate.

4. If required by the risk assessment, geoenvironmental engineer to supervise the

excavation/removal of contaminated material. Contaminated soils should be placed in a

bunded area and covered to prevent rainwater infiltration. To facilitate appropriate waste

disposal and potential re-use of materials all excavated soils should be segregated and

stockpiled depending on their soil classification.

5. Soil samples should be obtained by the geoenvironmental engineer from both the excavated

material, and the soils in the sides and base of the excavation to demonstrate that the full area

of contamination within the footprint of the works has been excavated. Where appropriate,

in-situ testing should be undertaken on the sides and base of the excavation to assess the

presence of residual contamination in the soils.

6. On receipt of chemical test results, the soils may be classified for disposal, or treatment if

appropriate, and dealt with accordingly.

7. Detailed records of the stockpile sizes, source and location should be kept and regularly

updated to allow materials to be easily tracked from excavation until leaving the site.

Records of excavated areas and the results of chemical testing should be incorporated within the final

verification report for the site.


CGN/ 04 275 K 26

9. VERIFICATION

Site inspections and compliance testing should be carried out during the works to demonstrate that the

requirements of this remediation strategy have been implemented, and records collated as follows

(where appropriate):

Site inspection records, photographs and measurements of excavations and stockpile

management;

Chemical testing of soils prior to disposal for waste classification (if disposal is required);

Verification of the thickness of the cover layer (already in-situ);

Details of unexpected contamination encountered and/or (potential) pollution incidents;

Details of pre-import test results for imported soils if required (source soil certification);

As built drawings (including depth of piles/pile caps and piling methodology used);

Duty of Care records for the storage, transport and disposal of soils where appropriate; and

Material management procedures (i.e. MMPs, permits, exemptions etc.) for re-used soils as

appropriate.

This information must be compiled and presented in a Verification Report for submission to the

Environment Agency and Local Authority as evidence of the remediation works carried out and should

also form part of the health and safety file for the site.


CGN/ 04 275 K 27

10. PILING WORKS RISK ASSESSMENT

10.1 Summary of Piling Options

The proposed development at LD131 will require piled foundations, with driven pre-cast piles being the

BBPT&D design team’s preferred option. Foundation modelling by Balfour Beatty of shallow

foundation solutions (e.g. a raft) indicates this is not likely to be feasible due to the low soil strength of

the landfilled material. The size of a raft solution would make it prohibitively expensive and would

generate considerable quantities of potentially hazardous waste if formed within the landfill, with

additional health and safety considerations for excavation teams. It is also not likely to be a sustainable

solution to remove landfilled materials from one landfill site for disposal at another, in addition to the

additional waste transportation impacts, such as on local air quality, for example.

A piled foundation solution is preferred therefore, using pre-cast concrete piles with a circular cross-

section. Mini piling was not considered suitable due to the thickness of soft ground conditions which

would require an excessive embedment depth into the underlying Mercia Mudstone Group, with high

volumes of spoil generated. This method would also have extended the work programme, increasing

health and safety risk to piling workers associated with working in landfill material.

Continuous Flight Auger (CFA) piling was also considered inappropriate given the volumes of waste

spoil created, as well as the potential for ground contaminants to impact upon the poured in situ

concrete.

The chosen pre-cast piles will be driven to a depth of approximately 18.0m bgl. This depth aligns with

slightly gravelly silty sand recorded as Destructured Weathered Mercia Mudstone Group4 (Secondary B

Aquifer). The depth to the Mercia Mudstone Group was proven to be approximately 17.7m bgl to

greater than 20.0 m bgl during the CGL ground investigation4. Significant frictional capacity is expected

to act upon the piles within the overlying 7m of predominantly cohesive Tidal Flat Deposits.

Pre-cast piles are driven into the ground using a top driven hydraulic hammer mounted on a tracked rig

which drives pile segments of selected lengths into the ground to the required founding depth. This

piling method compacts and densifies the surrounding ground effectively decreasing the in-situ

permeability of soils in close proximity to the piles thereby reducing the potential for downward

migration of mobile sources of contamination. Research suggests that significant vertical displacement


CGN/ 04 275 K 28

of contamination is unlikely to extend beyond 1.5 pile diameters from the centreline of a cylindrical

pile29.

Furthermore, solid cylindrical piles are expected to effectively self-seal when driven through a clay

layer with a thickness of 2 or more pile diameters, which would preserve the integrity of such a layer if

it was acting as an aquitard29. The recorded thickness of the Tidal Flat Deposits at the site is 7m. The

pile diameter is understood to be 300mm and so the calculated thickness of 2 x the pile diameter is

0.6m; more than 11 times less than the thickness of the Tidal Flat Deposits at this location.

In addition, the use of a moulded pile with a tapered end during pile construction means there is a

reduction in the potential for downward drag of contaminated soils during pile installation.

A driven piling method does not generate waste pile arisings during installation which is one of the

reasons for this piling method being the preferred choice at LD131 where arisings are anticipated to

contain landfill material. Surplus arisings generated following excavation and installation of the pile

caps is also to be avoided by installation of the pile caps within a raised temporary working platform to

be installed on top of the landfill surface.

The risks to human health from piling have been considered in accordance with the National

Groundwater and Contaminated Land Centre report NC/99/73 guidance for piling on contaminated

sites30.

Site safety precautions should be undertaken during piling works, including, but not limited to, the

implementation of site safety procedures and provision of suitable personal and respiratory protective

equipment (PPE and RPE). Radiation monitoring and potential UXO risk will also need to be

considered. All site works should be undertaken in accordance with the guidelines prepared by the

Health and Safety Executive31.

10.2 Pollution Scenarios

The following six potential pollution scenarios are considered for a driven pre-cast piling technique:

Scenario 1) Creation of preferential pathways through a low permeability layer, allowing

migration and pollution of an aquifer;

29 Environment Agency “Piling in layered ground: risks to groundwater and archaeology” October 2006, Science Report

SC020074/SR 30 Environment Agency (2001). Piling and Penetrative Ground Improvement Methods on Land Affected by Contamination:

Guidance on Pollution Prevention. 31 HSE. (1991). Protection of Workers and the General Public during the Development of Contaminated Land, Guidance note HS(G)66


CGN/ 04 275 K 29

Scenario 2) Creation of preferential pathways through a low permeability layer, allowing

migration of ground gases/vapours towards the surface;

Scenario 3) Direct contact of construction workers with contaminated soil arisings brought to

the surface. The proposed piling method (pre-cast driven) does not generate waste spoil and

therefore no exposure to arisings will occur during construction. The pile caps are also to be

constructed above the surface of the landfill to avoid exposure to landfill materials and

generation of waste. This scenario is therefore not considered to be relevant and is not

considered further within this PWRA.

Scenario 4) Direct contact of the piles or foundations with contaminated soil or leachate

leading to degradation of materials.

Scenario 5) The driving of solid contaminants down into an aquifer during pile driving.

Scenario 6) Pollution of groundwater by concrete or bentonite / concrete grout. The use of

pre-cast concrete piles will mean the potential for concrete loss during installation is not a

viable pathway and therefore this scenario is not considered further within this PWRA.

The following sections consider in turn the relevant pollution scenarios to assess risks associated with

the use of driven pre-cast piles and to identify mitigation measures, where necessary.

10.2.1 Pollution Scenario 1

Creation of pathways through an aquitard to allow potential contamination of an aquifer.

The Made Ground at the site is underlain by 7.0 m of soft silty clays forming the Tidal Flat Deposits

which, in turn, overly weathered silty clays, sand and gravels of the Mercia Mudstone Group4. A

groundwater strike was recorded upon encountering the Tidal Flat Deposits at a depth of 10.7m which

rose to 5.96m within 20 minutes. Perched groundwater was also recorded within the landfill materials

at a depth of 5.9m bgl.

As discussed in Section 3, the deeper groundwater strike is considered to have been subject to the

same hydraulic head as that within the landfilled material during drilling, having previously been

confined either by the bentonite seal installed as part of clean drilling techniques or the cohesive clay

layer at the base of the Made Ground. The upward hydraulic gradient within the Tidal Flat Deposits

will act to reduce the potential downward migration of mobile contaminants from the landfill to the

Secondary B Aquifer.


CGN/ 04 275 K 30

There is no evidence to suggest the presence of a site-wide engineered landfill liner which would

protect groundwater beneath the landfill site; however, the Tidal Flat Deposits are classified as

Unproductive Strata by the Environment Agency and these cohesive strata will afford some protection

the underlying Mercia Mudstone Group Secondary B aquifer.

The current piling design indicates piles will terminate at a depth of 18.0m bgl within a sandy layer of

weathered Mercia Mudstone Group bedrock. This will require the piling works to pass through the

landfill materials and the Unproductive Tidal Flat Deposits. However, as the thickness of the Tidal Flat

Deposits is 7m at LD131 (i.e. greater than 2 times the pile diameters) the action of piling is expected to

effectively self-seal and preserve the integrity of this predominantly cohesive layer which is considered

likely to be acting as an aquitard29.

In addition, piling works will be completed using a moulded tapered end which will reduce the

potential for downward drag of contaminated soils during pile installation.

Given the location of the site within the industrial area of Avonmouth Port and the anticipated low

sensitivity Secondary B Aquifer, it is considered unlikely the area would be suitable for future water

abstraction downgradient of the site. Given the scale of the redevelopment it is considered unlikely

the proposed piling works will introduce significant new pathways for the migration of concentrations

of mobile contamination that could significantly increase the risk of pollution to the Secondary B

Aquifer at this location.


Creation of preferential pathways through a low permeability surface layer, allowing migration of

soil gas or contaminated vapours to the surface.

A ground gas assessment has not been undertaken for the site and is outside the scope of this report.

Landfilled materials are present at the site which could have the potential to generate ground gas.

However, the absence of enclosed or confined spaces within the tower development in which ground

gas could accumulate, is taken to indicate the potential risk of exposure is not a viable pathway.

During construction it is assumed that short-term construction risks associated with exposure to

ground gas will be mitigated through the implementation of working practices usual on UK

construction sites. This includes site (and contamination) specific risk assessments prepared by the

Contractor and use of appropriate personal and respiratory protective equipment (PPE and RPE).

Prevention and/or control of entry into confined spaces to protect against potential exposure to

ground gas and/or vapours is also required.


CGN/ 04 275 K 31


Direct contact of the piles with contaminated soil or leachate causing degradation of materials.

The proposed pre-cast piles will be formed of concrete designed to resist the contamination identified

on site and in accordance with the BBPT&D assessment with respect to potentially aggressive soils.

During the CGL ground investigation a strong odour of hydrocarbon was recorded between depths of

5.8m and 10.2m bgl, however, no visual evidence of hydrocarbon or free product was recorded. It is

considered unlikely there are concentrations of hydrocarbon present that could affect concrete curing;

however, given the piles will be constructed of pre-cast concrete this is less of a concern.

Based on the assessment undertaken by BBPT&D buried concrete should be designed to ACEC Class

AC-2 in accordance with BRE guidance28.


The pushing of contaminants down into an aquifer during pile driving

The proposed piling depth is to be terminated at 18.0m bgl within Destructured (Grade IVa) sands of

the Mercia Mudstone Group. The use of a moulded pre-tapered end during pile construction will

reduce the potential for downward drag of contaminated soils during pile installation and the pile is

expected to self-seal because the overlying cohesive Tidal Flat Deposits are greater than 2 times the

pile diameter29.

The chosen piling method also compacts and densifies the surrounding ground around the pile,

effectively decreasing the in-situ permeability of soils in close proximity to the pile thereby reducing

the potential for downward migration of mobile sources of contamination.

The installation of driven pre-cast concrete piles is therefore not considered to significantly increase

the potential for pollution of the aquifer beneath the site.

10.3 Conclusions

Based on this piling works risk assessment, the construction of pre-cast concrete driven piles toed into

the surface of the Mercia Mudstone Group by a specialist piling contractor, using a moulded pre-

tapered end, is considered unlikely to increase the risk of contamination to controlled waters and other

identified potential receptors given the scale of the redevelopment and the surrounding current and

historical land use.


CGN/ 04 275 K 32

Potential risk to construction workers due to exposure to contaminated soil arisings is not considered

to be viable with this piling methodology. The piling operations will be undertaken from the surface of

a temporary working platform on top of the landfill material and the excavations for the pile caps will

therefore be into imported material rather than into the landfill material.

Piling contractors should be referred to this PWRA and to the CGL Ground Investigation Report4 for

details of the landfilled materials and contamination migration potential at the site in order for due

care to be incorporated into the piling methodology, including with respect to the potential for landfill

gas, radiation and UXO.

FIGURES

Client Project Job No

Balfour Beatty Power Transmission and

Distribution Hinkley Point C Connection 400kV OHL North and Avonmouth CGN/04275K

Title

Site Location Plan

Figure 1a




Title

Site Location Plan

Figure 1b




Title

Site Location Plan

Figure 1c




Title

Site Location Plan

Figure 1d




Title

Site Location Plan

Figure 1e

SOFT SILTY CLAY WITHOCCASIONAL SAND BANDS

MERCIA MUDSTONE

CONCRETEPILE CAPS

LD131 Tower

TIDAL FLAT DEPOSITS(UNPRODUCTIVE STRATA)

MADE GROUND

LANDFILL MATERIAL(a)

(a) Source - landfill materials(SECONDARY B AQUIFER)

TEMPORARYFLOATING ROADS

AND WORKINGPLATFORM - TO BE

REMOVEDFOLLOWING

CONSTRUCTION

~10m

~7m

>1000m

[LOW PERMEABILITY)

[LOW PERMEABILITY)

POTENTIAL MIGRATIONPATHWAY TO

SECONDARY B AQUIFERMITIGATED BY COHESIVE

DEPOSITS BEING >2 XPILE DIAMETER AND USE

OF A TAPERED PILESHAFT


Title

Balfour Beatty PowerTransmission & Distribution

Hinkley Point C Connection 400kV OHL - North and Avonmouth CGN/04275K

LD131 Tower Layout and Post-DevelopmentConceptual Site Model

Drawn by

Checked by

Approved by

TSB

N

Figure 2

Section Plan

MCK

RNS

Groundwater strikeKEY

Working areaKEY

APPENDIX A Piling Sectional Profile

HI NKLEY POI NT C CO N NEC TIO N 4 00K V O HL - NOR TH A ND A VO NMOUT H Remediation Method Statement and Piling Works Risk Assessment

Appendix A. Pre-Cast Concrete Piling Design – LD131

Borehole Legend

Pile Design Depth

APPENDIX B Remedial Options Appraisal

HI NKLEY POI NT C CO N NEC TIO N 4 00K V O HL - NOR TH A ND A VO NMOUT H Rem ediat ion Me thod Sta t ement and P i l ing Wo rks R isk Assessm ent Appen di x B – Rem edia l Op t io n s Appra isa l

Remedial technique Synopsis

Suita

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for

Deve

lopm

ent

Suita

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for

cont

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atio

n?

Will

con

stra

ints

pe

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Appl

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Comment

Civil Engineering Options

Containment - cover systems

Provision of a physical break in a contaminant linkage by removing the pathway between source and receptor. A ‘capping layer’ forms a barrier of clean soil above contaminated soils.

This method would provide a cost effective and rapid solution that could be easily implemented during the construction programme. The site lies within an undeveloped grassed landfill site. The landfill is reported to have an installed cover comprising thermally dried sewage sludge. Chemical testing of this material did not detect unacceptable concentrations of contamination and so this material is likely to be suitable as a cover layer if reinstated/left in-situ.

Alternatively, a compacted low permeability ground cover would provide an effective cover layer that would prevent potential exposure to contamination in underlying Made Ground.

The presence of a cover will reduce infiltration of rainwater and mitigate potential downward mobilisation of contaminants into the underlying Secondary B Aquifer.

Containment - in ground barriers

Vertical barrier or cut-off wall used to control the horizontal spread of contaminants, usually in groundwater.

X X X

The contamination recorded is not constrained to the OHL tower site and therefore an in ground barrier would not be effective. This option is also likely to add significant time to the construction programme and therefore is not considered to be viable.

Excavation and disposal or off-site treatment

Removing soils to treat or dispose of them elsewhere.

This method has historically been favoured due to it being a rapid solution. However, the use of floating roads and working pads above the level of the landfill at this location means it is not necessary to excavate into the landfill.

Chemical

Soil flushing In-situ chemical remediation by introducing chemicals directly into soil or groundwater to destroy contaminants or convert them to less harmful products.

X ? X X

This method would require additional drilling and installation of extraction wells to collect injected water. This method is likely to take several weeks to implement and may not be efficient with metal contamination. It is therefore not considered viable within the Hinkley project construction programme.

Surface amendments A soil amendment refers to any material added to the soil to improve its physical or chemical properties. Soil amendments aim to reduce exposure by limiting exposure pathways and immobilizing contaminants to limit their bioavailability.

X ? X X

This method is more relevant to regeneration projects over large areas and over long periods of time. This method is therefore not considered viable within the Hinkley project construction programme.

http://www.trm-ltd.com/case-studies/operational-manufacturing-facility

http://www.trm-ltd.com/case-studies/operational-manufacturing-facility


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Physical

Soil washing

An ex-situ technique that removes hazardous contaminants that preferentially bind to the finer grained fraction of soils (silts and clays). The main goal is to separate the contaminated fines and wash water from more coarse grained soils.

X X X X

This method is likely to be economically viable only with large volumes of suitable material and requires time and space to stockpile and dry treated soils. At the end of the process, a contaminated sludge requires disposal off site and this is not in line with the Hinkley project Zero Waste policy. Unless a treatment hub is installed to take soils from multiple sites, this method is not likely to be viable given the isolated nature of the OHL tower sites and low treatment volumes within the Hinkley project.

Biological

Biopiles/bioventing/

Biosparging/

Landfarming/slurry phase biotreatment/

windrow turning

Ex-situ and in-situ biological remediation techniques rely on the use of microorganisms to biodegrade organic constituents, often using addition of air (or oxygen) and nutrients to increase the biological activity.

X ? X X

These methods can be suitable for treating a range of contaminants, however, trials are usually required to ensure optimal conditions and because the landfill extends beyond the OHL tower site this treatment option is not considered likely to be cost effective or a durable solution at the tower location.

Stabilisation and solidification

Hydraulic binders

Contaminants are bound in the soil by mixing with binding agent(s) such as lime, PFA and/or cement. The product of stabilisation is a material in which the contaminants are bound in a matrix that is less permeable and may have an improved structural capacity.

X X X

This treatment process is relatively quick in relation to other options, however a period of laboratory testing by the remediation contractor is required to determine the correct binding agent ratio and this is unlikely to align with the current Hinkley construction programme.

Vitrification

Soil vitrification embeds contamination into a glass matrix so that hazardous substances cannot leak out. It requires high temperatures to melt the soil which solidifies into a glass on cooling.

X X X

The process will require excavation of impacted soils prior to treatment and is expensive and so economically viable only with large volumes of suitable material. It also requires time and space for treatment. Unless a treatment hub is installed to take soils from multiple sites, this method is not likely to be viable given the isolated nature of the OHL tower sites and low treatment volumes.

Thermal

Incineration

An alternative to final disposal at landfill. Soils are heated to very high temperatures to ensure complete destruction of contamination.

X X X

This technique is not considered to be a cost effective or a sustainable solution and does not align with the project Zero Waste policy.

Thermal desorption Thermal degradation of organic compounds in-situ or alternatively, remediation

X X X X This method of treatment is only suitable for organic contaminants and due to the high set up costs only


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of contaminants through non-destructive phase transfer processes.

considerable volumes of soil make this technique viable.

APPENDIX C Backfill Import Specification (Chemical)

HI NKLEY POI NT C CO N NEC TIO N 4 00K V O HL - NOR TH A ND A VO NMOUT H Remediation Method Statement and Piling Works Risk Assessment

Appendix C. Backfill Import Specification (Maximum Permissible Chemical Concentrations for Imported Fill)

Determinant

Maximum permissible

concentration1

(mg/kg)2 Rationale

1% SOM Arsenic 40 C4SL10 Beryllium 1.72 GAC4

Cadmium 150 C4SL10 Chromium (III) 887 GAC4 Chromium (VI) 21 C4SL10 Lead 310 GAC4 Mercury 75.3 GAC4 Selenium 596 GAC4 Copper 7130 GAC4 Nickel 182 GAC4 Zinc 40400 GAC4 Vanadium 651 GAC4 Benzo(a)pyrene 5.3 C4SL10 Benzo(a)anthracene 12.4 GAC4

Benzo(b)fluoranthene 4 GAC4 Benzo(k)fluoranthene 106 GAC4 Chrysene 30.7 GAC4 Dibenzo(a,h)anthracene 0.33 GAC4 Indeno(1,2,3-cd)pyrene 45.2 GAC4 Naphthalene 2.53 GAC4 Benzene 3.3 C4SL10 Toluene 1010 GAC4 Ethyl benzene 274 GAC4 Xylenes 87.7 GAC4 Sum of TPH aliphatic & aromatic C5-C10 < 1,000 Hazardous waste thresholds8 (C10+ MPC based on threshold for

C25+) Sum of TPH aliphatic & aromatic C10+ < 1,000 pH 5-10 Monohydric Phenols 1180 GAC4

Free Cyanide 34 GAC3

Asbestos No detectable fibres9

1. These maximum permissible concentrations (MPCs) are import criteria only and are not necessarily appropriate for human health risk assessment. 2. In mg/kg dry soil except pH and asbestos. 3. GAC for free cyanide derived by Atkins based on acute exposure for a 0-6 year old child. 4. Generic Assessment Criteria generated ‘in-house’ based on CLEA model Version 1.071. 5. Nable, Banuelos and Paul. (1997). Boron Toxicity. Plant and Soil, Vol. 193, pp1 81-198. 6. Speciated TPH values must not exceed GAC. Assessment of sum of TPH must also be made against hazardous waste threshold to confirm imported soils do not

classify as hazardous material. 7. GAC derived MPC for TPH fraction limited to 1,000mg/kg based on ‘waste thresholds’. 8. Environment Agency. (2007). A Guide to Hazardous Waste Regulations: How to find out if waste oil and waste that contain oil are hazardous. HWR08. 9. Laboratory screen by microscopy may be required subject to source of material. 10. Published C4SL (DEFRA, 2014)

APPENDIX D CGL Borehole Logs (LD130, LD131, LD132)

(1.20)

(2.80)

(1.70)

(2.80)

6.00

3.20

1.50

1.20

-1.60

0.305.44

01-05-2001-05-20

Dark brown slightly sandy gravelly CLAY. Sand is fine to coarse. Gravel isangular to subangular fine to coarse of concrete, red brick, sandstone,mudstone and limestone.[MADE GROUND]

Dark greyish brown slightly sandy gravelly silty CLAY. Sand is fine tocoarse. Gravel is angular fine to coarse of concrete, red brick, mudstone,sandstone and limestone. Frequent fragments of plastic, metal, wood,timber, wire and plastic bags.[MADE GROUND]

Greenish grey gravelly silty CLAY. Gravel is angular fine to coarse ofconcrete, mudstone and red brick. Frequent fragments of timber, plastic,metal and wire.[MADE GROUND]

Firm grey mottled brown gravelly silty CLAY. Gravel is angular fine tocoarse of mudstone and limestone.[MADE GROUND - REWORKED TIDAL FLAT DEPOSITS]Firm grey mottled brown silty CLAY. Rare angular fine mudstone andlimestone gravel. Occasional shell fragments.[TIDAL FLAT DEPOSITS]

7.50 Becomes gravelly. Gravel is angular to subrounded fine to coarse oflimestone and mudstone.

Soft dark grey slightly sandy silty CLAY.[TIDAL FLAT DEPOSITS]

1.20

4.00

5.70

6.00

8.80

0.308.80

0.40-0.50 B0.50 ES0.80-0.90 B

1.20-1.65 B/D1.20 SPT N6

2.00-2.45 B/D2.00 ES2.00 SPT N7

3.00-3.45 B/D3.00 SPT N5

4.00-4.45 B/D4.00 SPT N6

5.00-5.45 B/D5.00 SPT N8

5.70-5.80 B

6.00-6.45 UT 43 blows

6.45-6.50 B

7.50-7.95 B/D7.50 SPT N5

8.80-8.90 B9.00-9.45 B/D9.00 SPT N3

Depth (m)Depth(m) LegendW

ater

Casing

SAMPLES & TESTS

1 of 2

ReducedLevel

Depth

Boring Progress and Water Observations

BOREHOLE No

TestResult (Thick-

ness)

STRATA

Dia. mm

BOREHOLE LOG

StandingDepthDate Comment Strike

Depth

DESCRIPTIONTypeNo

Hinkley Point C Connection 400kV OHL North and AvonmouthProject

Job No Date Ground Level (m)

7.20Sheet

Balfour Beatty Power Transmission & DistributionClient

01-05-20 E 354,017.2 N 181,671.1Co-Ordinates (m)

Field CrewMethod/Plant Used

Checked ByLogged By

General Remarks

LD130

1. Borehole scanned and set out in accordance with BBPT&D AWNES procedure.The pit was then scanned at 300mm intervals by the CGL engineer to 1.20m bgl.2. B - Bulk sample, D - Disturbed sample, ES - Environmental sample, SPT -Standard penetration test, UT - UT100 sample, HSV - Hand Shear Vane (Avg. ofthree readings)3. Borehole terminated at 15.80m bgl following an hour of chiselling onmudstone bedrock, as requested by BBPT&D design.4. Borehole backfilled with a mixture of bentonite and arisings.5. Strong hydrocarbon odour from 1.20m - 3.00m bgl, becoming less pronouncedfrom 3.00 - 4.00m bgl.

Bainbridge Brothers Limited FAM MJSDando 2000

CGN/04275B

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(4.10)

(2.40)

(0.50)

-5.70

-8.10

-8.60

2.6001-05-20

Soft dark grey slightly sandy silty CLAY.[TIDAL FLAT DEPOSITS] (continued)

Firm becoming very stiff reddish brown silty slightly gravelly CLAY. Gravelis angular fine of mudstone.[DESTRUCTURED MERCIA MUDSTONE GROUP - GRADE IVa]

Very dense reddish brown GRAVEL. Gravel is angular fine of mudstone.[DISTINCTLY WEATHERED MERCIA MUDSTONE GROUP - GRADE III]

(Borehole terminated at 15.8m)

12.90

15.30

15.80

15.20

10.50-10.95 B/D10.50 SPT N4

12.00-12.10 B

12.90-13.00 B

13.50-13.95 B/D13.50 SPT N47

15.00-15.45 B/D15.00 SPT N50/

185 mm


ater

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SAMPLES & TESTS

2 of 2

ReducedLevel

Depth


BOREHOLE No

TestResult (Thick-

ness)

STRATA

Dia. mm

BOREHOLE LOG


Depth

DESCRIPTIONTypeNo



7.20Sheet


01-05-20 E 354,017.2 N 181,671.1Co-Ordinates (m)


Checked ByLogged By

General Remarks

LD130

1. Borehole scanned and set out in accordance with BBPT&D AWNES procedure.The pit was then scanned at 300mm intervals by the CGL engineer to 1.20m bgl.2. B - Bulk sample, D - Disturbed sample, ES - Environmental sample, SPT -Standard penetration test, UT - UT100 sample, HSV - Hand Shear Vane (Avg. ofthree readings)3. Borehole terminated at 15.80m bgl following an hour of chiselling onmudstone bedrock, as requested by BBPT&D design.4. Borehole backfilled with a mixture of bentonite and arisings.5. Strong hydrocarbon odour from 1.20m - 3.00m bgl, becoming less pronouncedfrom 3.00 - 4.00m bgl.


CGN/04275B

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(0.80)

(2.20)

(2.80)

(1.20)

(3.20)

11.28

9.08

6.28

5.08

5.2714-05-20

Dark brown slightly sandy slightly gravelly CLAY. Sand is fine to coarse.Gravel is angular to subangular fine to coarse of red brick, concrete andmudstone.[TOPSOIL]Dark brown mottled black gravelly silty CLAY. Gravel is angular fine tocoarse of sandstone, mudstone, concrete and red brick. Frequentfragments of pottery, timber, wood, glass and metal wire.[MADE GROUND]

Reddish brown slightly sandy slightly gravelly silty CLAY. Sand is fine tocoarse. Gravel is angular to subangular fine to coarse of mudstone, redbrick, concrete. Frequent fragments of pottery, timber, wood, glass andmetal wire.[MADE GROUND]

Black slightly clayey sandy GRAVEL of angular fine metal fragments withfrequent fragments of glass, plastic and wood, tin cans, bin bags andwire. Sand is fine to coarse.[MADE GROUND]

Black slightly clayey sandy GRAVEL of angular fine to coarse metalfragments, brick and concrete with frequent fragments of glass, plasticand wood, tin cans, bin bags and wire. Sand is fine to coarse.[MADE GROUND]7.00 Increasing concrete and red brick gravel content.

0.80

3.00

5.80

7.00

5.90

0.10-0.20 B

0.40-0.50 B0.50 ES0.80-0.90 B1.00 ES1.20-1.65 B1.20-1.65 D1.20 SPT N6

2.00 ES2.00-2.45 UT 26 blows2.45-2.50 B

3.00-3.45 B3.00-3.45 D3.00 SPT N8

4.00-4.45 UT 24 blows

4.45-4.50 B

5.00-5.45 B5.00-5.45 D5.00 SPT N7

5.80-5.90 B6.00-6.45 B6.00-6.45 D6.00 SPT N7

7.50-7.95 B7.50-7.95 D7.50 SPT N8

9.00-9.45 B9.00-9.45 D9.00 SPT N6


ater

Casing

SAMPLES & TESTS

1 of 3

ReducedLevel

Depth


BOREHOLE No

TestResult (Thick-

ness)

STRATA

Dia. mm

BOREHOLE LOG


Depth

DESCRIPTIONTypeNo



12.08Sheet


14-05-20 E 353,913.9 N 181,929.2Co-Ordinates (m)


Checked ByLogged By

General Remarks

LD131

1. Borehole scanned and set out in accordance with BBPT&D AWNES procedure.The pit was then scanned at 300mm intervals by the CGL engineer to 1.20m bgl.2. B - Bulk sample, D - Disturbed sample, ES - Environmental sample, SPT -Standard penetration test, UT - UT100 sample, HSV - Hand Shear Vane (Avg. ofthree readings)3. Borehole terminated at 20.00m bgl following an hour of chiselling onmudstone bedrock, as requested by BBPT&D design.4. Borehole backfilled with a mixture of bentonite and arisings.5. Strong hydrocarbon odour from 5.80 - 10.20m bgl.6. All arisings screened with a geiger counter upon recovery. No materialregistered above background levels.7. Borehole was sealed with 2.00m of bentonite plug at 10.70m bgl before theborehole was progressed into the underlying natural material.


CGN/04275B

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(0.50)

(5.80)

(1.20)

(1.30)

(0.70)

1.88

1.38

-4.42

-5.62

-5.92

-7.22

-7.92

5.9614-05-20

Soft light grey slightly sandy silty CLAY. Sand is fine.[MADE GROUND - POTENTIAL LANDFILL BASE LINER]

Soft light grey silty CLAY with occasional sand bands. Sand is fine.[TIDAL FLAT DEPOSITS]

Soft dark grey silty CLAY.[TIDAL FLAT DEPOSITS]

Firm reddish brown slightly gravelly silty CLAY. Gravel is angular fine ofmudstone.[DESTRUCTURED MERCIA MUDSTONE GROUP - GRADE IVa]Reddish brown slightly gravelly silty SAND. Sand is fine to coarse. Gravel isangular fine of mudstone.[DESTRUCTURED MERCIA MUDSTONE GROUP - GRADE IVa]


(Borehole terminated at 20m)

10.20

10.70

16.50

17.70

18.00

19.30

20.00

10.70

10.50-10.95 B10.50-10.95 D10.50 SPT N1

12.00-12.10 B

13.50-13.95 B13.50-13.95 D13.50 SPT N5

15.00-15.10 B

16.50-16.95 UT 14 blows

16.95-17.00 D

17.70-17.80 B

18.00-18.10 B

19.30-19.40 B19.50-19.95 B19.50-19.95 D


ater

Casing

SAMPLES & TESTS

2 of 3

ReducedLevel

Depth


BOREHOLE No

TestResult (Thick-

ness)

STRATA

Dia. mm

BOREHOLE LOG


Depth

DESCRIPTIONTypeNo



12.08Sheet


14-05-20 E 353,913.9 N 181,929.2Co-Ordinates (m)


Checked ByLogged By

General Remarks

LD131



CGN/04275B

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19.50 SPT N50/0 mm


ater

Casing

SAMPLES & TESTS

3 of 3

ReducedLevel

Depth


BOREHOLE No

TestResult (Thick-

ness)

STRATA

Dia. mm

BOREHOLE LOG


Depth

DESCRIPTIONTypeNo



12.08Sheet


14-05-20 E 353,913.9 N 181,929.2Co-Ordinates (m)


Checked ByLogged By

General Remarks

LD131



CGN/04275B

Rep

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|| D

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ovem

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Inst

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/Bac

kfill

(2.20)

(1.30)

(1.20)

(5.20)

11.09

8.89

7.59

6.39

3.674.32

15-05-2015-05-20

Dark brown slightly sandy slightly gravelly CLAY. Sand is fine to coarse.Gravel is angular to subangular fine to coarse of red brick, concrete andmudstone.[TOPSOIL]Dark brown mottled black gravelly silty CLAY. Gravel is angular fine tocoarse of sandstone, mudstone, concrete and red brick. Frequentfragments of pottery, timber, wood, glass and metal wire.[MADE GROUND]

Reddish brown slightly sandy slightly gravelly silty CLAY. Sand is fine tocoarse. Gravel is angular to subangular fine to coarse of mudstone, redbrick, concrete. Frequent fragments of pottery, timber, wood, glass andmetal wire.[MADE GROUND]

Black slightly sandy gravelly CLAY. Sand is fine to coarse with high ashcontent. Gravel is angular fine of metal, bituminous macadam, red brickand concrete. Frequent fragments of glass, cans, bin bags, metal wire,plastic, slate and wood.[MADE GROUND]

Black slightly clayey sandy GRAVEL. Sand is fine to coarse. Gravel isangular fine of metal. Frequent fragments of glass, cans, bin bags, metalwire, plastic and wood.[MADE GROUND]

0.40

2.60

3.90

5.10

3.905.10

0.10-0.20 B

0.40-0.50 B0.50 ES0.80-0.90 B1.00 ES1.20-1.65 UT

1.65-1.70 B 28 blows

2.00-2.45 B2.00-2.45 D2.00 ES2.00 SPT N7

3.00-3.45 UT 38 blows

3.45-3.50 B

4.00-4.45 B4.00-4.45 D4.00 SPT N5

5.00-5.45 B5.00-5.45 D5.00 SPT N3

6.00-6.45 B6.00-6.45 D6.00 SPT N50/

0 mm

7.50-7.95 B7.50-7.95 D7.50 SPT N10

9.00-9.45 B9.00-9.45 D9.00 SPT N50/

150 mm


ater

Casing

SAMPLES & TESTS

1 of 3

ReducedLevel

Depth


BOREHOLE No

TestResult (Thick-

ness)

STRATA

Dia. mm

BOREHOLE LOG


Depth

DESCRIPTIONTypeNo



11.49Sheet


15-05-20 E 353,711.4 N 182,157.0Co-Ordinates (m)


Checked ByLogged By

General Remarks

LD132



CGN/04275B

Rep

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D:

CG

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H L

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AG

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|| D

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6 N

ovem

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Inst

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ent

/Bac

kfill

(7.90)

(1.20)

1.19

-6.71-6.91

-8.11

-8.51

9.4515-05-20

Soft light grey silty CLAY with occasional sand bands. Sand is fine.[TIDAL FLAT DEPOSITS]

Soft dark grey mottled green silty CLAY.[TIDAL FLAT DEPOSITS]Firm becoming stiff reddish brown slightly gravelly silty CLAY. Gravel isangular fine of mudstone.[DESTRUCTURED MERCIA MUDSTONE GROUP - GRADE IVa]


10.30

18.2018.40

19.60

20.00

11.30

10.30-10.40 B10.50-10.95 B10.50-10.95 D10.50 SPT N2

12.00-12.10 B

13.50-13.95 B13.50-13.95 D13.50 SPT N3

15.00-15.10 B

16.50-16.95 B16.50-16.95 D16.50 SPT N6

18.00-18.10 B18.20-18.30 B18.40-18.50 B

19.50-19.95 B19.50-19.95 D


ater

Casing

SAMPLES & TESTS

2 of 3

ReducedLevel

Depth


BOREHOLE No

TestResult (Thick-

ness)

STRATA

Dia. mm

BOREHOLE LOG


Depth

DESCRIPTIONTypeNo



11.49Sheet


15-05-20 E 353,711.4 N 182,157.0Co-Ordinates (m)


Checked ByLogged By

General Remarks

LD132



CGN/04275B

Rep

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D:

CG

L B

H L

OG

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CG

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_C H

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ovem

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2020

Inst

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/Bac

kfill

(Borehole terminated at 20m)19.50 SPT N50/160 mm


ater

Casing

SAMPLES & TESTS

3 of 3

ReducedLevel

Depth


BOREHOLE No

TestResult (Thick-

ness)

STRATA

Dia. mm

BOREHOLE LOG


Depth

DESCRIPTIONTypeNo



11.49Sheet


15-05-20 E 353,711.4 N 182,157.0Co-Ordinates (m)


Checked ByLogged By

General Remarks

LD132



CGN/04275B

Rep

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6 N

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Inst

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kfill

hinkley point c connection 400kv ohl – north and avonmouth

Documents