Appendix A.2 – Site Investigation Results

Land at Gibraltar Way, Chatham Surface Water Management Strategy

Appendices

Appendix A.2 – Site Investigation Results

Project:

Project ID:

Client:

Gibraltar Farm, Ham Lane, Hempstead, Gillingham, Kent

GTS-14-398

KD, SJ & MC Attwood

S I T E I N V E S T I G A T I O N

PHASE 1 DESK STUDY REPORT

Maple Road

Kings Lynn

Norfolk

PE34 3AF

Tel: 01553 817657

www.groundtechnology.co.uk

Report Reference GTS-14-398

Date: July 2014

Site:

Gibraltar Farm, Ham Lane,

Hempstead, Gillingham,

Kent,

Engineer:

Create Consulting Engineers Ltd (Create)

15 Princes Street

Norwich

Norfolk, NR3 1AF

GT

S-14-398, G

ibraltar Farm

, Ham

Lane, Hem

pstead, Gillingham

, Kent

Client:

KD, SJ & MC Attwood

Page ii

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Project ID: GTS-14-398 Site: Gibraltar Farm, Ham Lane, Lords Wood, Kent, ME7 3JJ Client: Create Consulting Engineers Ltd Date: July 2014 Report Written by: G Day BSc MSc Geo-environmental Engineer

Checked and Authorised for issue: B Armstrong BSc, MSc, FGS General Manager

GENERAL CONDITIONS / LIMITATIONS RELATING TO SITE INVESTIGATIONS

The recommendations of this report are based on the findings of a site walkover, an assessment of historical and environmental data provided by Envirocheck, and a series of exploratory holes and carried out at specified locations across the site. It is possible that conditions exist other than those encountered and therefore no guarantee can be given as to the extent to which the findings are representative.

It should be noted that groundwater conditions fluctuate according to seasonal and other factors, which cannot be predicted with certainty. In low permeability soils equilibrium ground water levels are rarely established during the period of fieldwork.

All recommendations made are subject to any relevant statutory regulations in force concerning design methods and safe construction practice. In addition unless specifically stated no account has been taken of possible subsidence due to mineral extraction.

This report is for the sole and specific use of the client and Ground Technology Services Limited and 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 report should be so copied, but no professional liability or warranty shall be extended to other parties by Ground Technology Services Limited in this connection without written consent.

The copyright of this report and other plans and documents prepared by Ground Technology Services Limited are owned by them.

Document Control

Page iii

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Contents

Appendices

Appendix A Exploratory Borehole Records

Appendix B Soakaway and Constant Head Permeability Test Results

Appendix C Historical Maps and Envirocheck Report

Appendix D Site Photographs

Appendix E Exploratory Hole Location Plan and Site Masterplan

Site Details Page 1

Preliminary Conceptual Model Page 8

Fieldwork Page 10

Ground Conditions Page 11

Comments and Recommendations Page 13

References Page 17

Further Works Page 16

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1.1 General Introduction Ground Technology Services Limited (GTS) were instructed by Create Consulting Engineers Ltd (Create) to complete a Phase 1 Desk Study Report in conjunction with a series of trial pit soakaway tests for a proposed residential development. A further phase of investigation comprising borehole drilling and constant head permeability testing was also undertaken to establish the drainage characteristics of the deeper soils in order to confirm drainage design. This report combines the findings of the desk study and trial pits soakaway testing carried out with the later phase of drilling and constant head tests. The proposed development is to comprise a new residential housing estate, with associated gardens, footpaths, access roads and landscaped areas. The current proposal is outlined on the Masterplan in Appendix E. 1.2 Objectives The objective of the Phase 1 Desk Study is to produce a preliminary site conceptual model to assess geotechnical and environmental risks for the site. The objective of the intrusive works is to undertake a series of trial pit soakaway tests to BRE 365 to confirm the near surface soil drainage characteristics, and also to drill a series of boreholes and carry out constant head permeability tests to confirm deeper soil drainage characteristics, in order to provide information for soakaway design. 1.3 Scope The scope of works for desk study assessment comprised: A site walkover to confirm and assess the

site in its current condition. A review of the available historical ordnance

survey maps. A review of environmental and geological

data within an Envirocheck report. Production of desk study report and

preliminary site conceptual model. The scope of works for the intrusive drainage investigation comprised: Nine mechanically excavated trial pits.

3 soakaway test locations in accordance with BRE 365.

5 Cable percussive boreholes to a depth of 20m.

10 constant head permeability tests; 2 in each borehole using different response zones.

2.1 Location and Description The irregular shaped site is located immediately south of Ham Lane, between Lords Wood and Hempstead, some 5km south of the town centre of Gillingham and is approximately 25.8 hectares in size. The site is predominately arable farmland. National Grid Reference 578349 162796 approximately identifies the central part of the site. The site slopes to north west, with elevations at the site ranging from 130mAOD to the south and 115m AOD to the north and north west. A detailed description of the site is contained within section 2.6.1. 2.2 Geology The available information1 indicates the solid geology underlying the site is the Seaford Chalk Formation (Cretaceous period). The Lewes Nodular Chalk Formation, also of the Cretaceous period, which underlies the Seaford Chalk Formation is indicated as the bedrock geology in the southern areas of the site. Nearby BGS borehole logs from previous works undertaken within this area indicate white CHALK with occasional flints. This solid geology is overlain by Head deposits to the north of the site and Clay With Flints Formation to the western and eastern areas of the site. Locally, no drift deposits are indicated within the central area of the site. Made Ground was not indicated during the site visit. 2.3 Hydrology The site is located approximately 6km to the south of the estuary of the River Medway. The low lying land approximately 1km to the north west is situated within areas at risk from flooding and extreme flooding. The site itself is not considered at risk from flooding or extreme

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flooding as indicated on the flood map extract presented on the flowing page. 2.4 Hydrogeology The Hydrogeology of the site is likely to be characterised by the Seaford Chalk Formation and the Lewes Nodular Chalk Formation, which are both classified as Principle Aquifers. These are deposits that have high intergranular and/or fracture permeability meaning they usually provide a high level of water storage. They may support water supply and/or river base flow on a strategic scale. Given the proximity of the River Medway to the north, and the sloping topography towards the northwest, the anticipated direction of groundwater flow is likely to be to the north west and north. However cohesive layers within the Head deposits and Clay With Flints Formation may yield perched groundwater levels. The groundwater below the site is likely to be in hydraulic continuity with the nearby River Medway. Given the elevation of the River (4mAOD), groundwater levels undying the site are anticipated to be between 111mbgl and 126mbgl, although perched water within the variable Head deposits and Clay With Flints Formation could be encountered.

The site is situated within a zone 3 source

protection zone (SPZ). The soils are defined as having an Intermediate to High Leaching potential (U, H1, L1). These are defined as soils which readily transmit liquid discharges because they are either shallow, or susceptible to rapid by-pass flow directly to rock, gravel or groundwater.

The site is not situated within a Nitrate Vulnerable Zone (NVZ).

2.5 Chalk-Related Subsidence Risk Assessment

The presence of chalk at relatively shallow depths beneath the site indicates that the possibility of subsidence, related to swallow holes and other chalk solution features or man made cavities, should be considered. The desk study information has identified two known solution features. These are located 199m and 243m south east of the site, respectively. On the basis of the predictive numerical subsidence risk model for natural solution features, after Edmonds12, the site appears to fall into the moderate subsidence risk category.

Section 2: Site Details

Flood Map

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2.6 Desk Study Information 2.6.1 Site walkover A site walkover survey was completed on the 14th April 2014, by an engineer from GTS. Relevant information is presented below and photographs of the site are presented in Appendix D.

Item Description

Site Access Access to the site is gained by Ham Lane to the north of the site.

Site Boundaries and Usage Hall Wood lies to the western boundary, between the site and Lord’s Wood. Roots Wood and Holts Wood are situated to the north.

Within Hall Wood lies a fenced compound with buildings currently used as a builders yard, marked as depot.

The site is bounded to the north by Ham Lane with a farmyard beyond the north western corner of the site. The farmyard buildings are now utilised for commercial purposes, comprising a haulage business in the southern building and a double glazing and conservatory business in the northern buildings.

An above ground fuel storage tank associated with the haulage business at Gibraltar Farm was noted.

A compound within Hall Wood was also noted, but was not inspected further during the site walkover.

Services Telephone Line: An overhead telephone line runs from the southern area of the site towards the farmyard buildings to north western corner of the site, passing to the east of Roots Wood.

Topography The site generally slopes from east south east to west north west from an elevation of approximately 130mAOD to 115mAOD.


Table 1: Summary of Site Walkover

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2.6.2 Historical Map Review The development history and land usage of the site, together with its immediate environs, has been researched from early Ordnance Survey (OS) maps, dating from 1869 to the present day. Extracts from these maps are presented in Appendix B. Changes to the site and its surroundings are summarised on the following pages. The first available map edition, dated 1869, indicates that the site is almost entirely undeveloped, situated within 2 fields with woodland in the eastern and southern areas. Agricultural buildings associated with Gibraltar Farm are indicated approximately 100m to the north west of the site. The surrounding land is predominately undeveloped, with Hall Wood and Lord’s Wood situated immediately to the west.

Date Site Surroundings

1898 The site remains unchanged. The surrounding area remains relatively unchanged. However a Chalk Pit is indicated immediately to the north western boundary and an Old Gravel Pit is indicated some 500m to the north east.

1909 The site remains unchanged. Further development of Gibraltar Farm. The Old Gravel Pit and Chalk Pit indicated in 1898 are now not indicated.

1932 The site remains unchanged. Residential development has occurred at Lords Wood.

1970 The site remains unchanged. Further residential development of Lord’s Wood with associated infrastructure developments such as a school. There is also further residential development to the north west. The M2 motorway is indicated to the south.

1975 The site remains unchanged. Further residential development of Lords Wood including a school. Industrial development at Lords Wood including buildings indicated as works and depot.

1869 OS Extract Map

Table 2: Historic Map Summary


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2.6.3 Historical Map Summary The site was shown as a agricultural field and woodland circa 1869. The site was developed over time, with the clearing of most of the woodland to make way for agricultural expansion. The surrounding area was predominately rural circa 1869, with large woodland areas and isolated dwellings and farms with a limited road network. Circa 1932, residential development began with the partial clearing of Lords Wood. The next phase of major development began in the 1970’s with residential and infrastructure development of Lords Wood, including the development of the M2 motorway to the south. The surrounding area received gradual residential and infrastructural development up to the present day.

Date Site Surroundings

1980 The site remains unchanged. Site previously labelled as Chapel Hill Wood is now labelled as a Shopping Centre.

1987 The site remains unchanged. New school identified approximately 500m to the west of the site, previously identified as Lords Wood. Building to the west north west previously identified as a Club is now identified as a Leisure Centre. Group of buildings to the south west previously identified as depot and works are now identified as an Industrial Estate.

1991 The site remains unchanged. Site to the north previously identified as Elm Court is now identified as Elm Court Industrial Estate and Car Park.

2006 The site remains unchanged. Building to the north of Elm Court Industrial Estate with associated car park is now labelled as a Garden Centre. Industrial Estate to the south west of the site is now labelled as Lords Wood Industrial Estate. Small Lake excavated to the east south east of Abbey Court Farm.

2014 The site remains unchanged. The surrounding area appears to be remain unchanged.

2014 OS Extract Map

Table 2 Continued: Historic Map Summary


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2.6.4 Envirocheck Report Review The Envirocheck Report, presented in Appendix C, has been reviewed and entries located on or in the immediate surroundings of the site (<250m) are considered below. Agency and Hydrological The soils are designated as Intermediate to High Leaching Potential (U & H1 and I1). These are soils which can transmit a wide range of pollutants and soils which readily transmit liquid discharges because they are either shallow, or susceptible to rapid by-passflow directly to rock, gravel or groundwater. Waste Hazardous Substances There are no entries for Hazardous Substances located on or in the immediate surroundings of the site.

Geological BGS Boreholes: One borehole is located within 250m of the site. Coal Mining Affected Areas: The site is in an area which may not be affected by coal mining. Potential for Collapsible Ground Stability Hazards: Very Low. Potential for Compressible Ground Stability Hazards: No Hazard. Potential for Ground Dissolution Stability Hazards: Very Low to High. Potential for Landslide Ground Stability Hazards: No Hazard to Very Low. Potential for Running Sand Ground Stability Hazards: No Hazard to Very Low Potential for Shrinking or Swelling Clay Ground Stability Hazards: No Hazard to Low

Data Type On Site Within 250m

Contaminated Land Register Entries and Notices

None Recorded None Recorded

Discharge Consents None Recorded None Recorded

Integrated Pollution and Prevention Controls


Local Authority Pollution and Prevention Controls

None Recorded None recorded within 250m of the site. 1 Recorded within 500m of the site and is related to recycling.

Local Authority Pollution and Prevention Controls

Enforcements


Pollution incidents to controlled water


Prosecutions Relating to Authorised Processes


Water Abstractions None Recorded None Recorded

Water Industry Act Referrals None Recorded None Recorded

Table 3: Agency and Hydrological Summary Table


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Radon Affected Areas and Radon Protection Measures: The site is situated within an intermediate probability radon area, as between 1 and 3% of properties are above the action level. No radon protection measures are required for the construction of new dwellings or extensions.

Shallow Mining Hazards: No hazard on site.

Natural Cavities: 2 No. solution pipes are located 199m and 243m to the south east.

Potentially Infilled Land: An area of potentially infilled land (non water) is located <10m to the north west between the site and Gibraltar Farm relating to a former Chalk Pit. A former Gravel Pit is located 500m to the north east. 3 former Chalk pits are located >500m to the north and south west.

Industrial Land Use

Contemporary Trade Directory Entries: There are 21 located within 250m of the site boundary of the following classifications; Dry Cleaners, Window Frame Manufacturers, Industrial Services, Garage Services, Stair Lift Manufacturers, Car Dealers - Used, Joinery Manufacturers, Glass Fibre Moulding, Motor Cycle Repairs, Cladding Suppliers and Installers, Blinds Awnings and Canopies, Engineers (general), Confectionary Manufacturers, Swimming Pool Contractors, Car Body Repairs.

Fuel Station Entries: There are no fuel station entries within 250m of the site.

Sensitive Land Use

Nitrate Vulnerable Zone (NVZ): The surface water and groundwater beneath the site is not within a Nitrate Vulnerable Zone

Environmentally Sensitive Area: The site is not situated within an Environmentally Sensitive Area.

2.6.5 Envirocheck Report Summary

The Envirocheck Report has identified that there are no landfills, waste treatment facilities, discharge consents or contaminated land entries within 250m of the site. An area of non water infilled land is situated approximately <10m to the north west of the site.

The underlying soils are of intermediate to high leaching potential and the bedrock is a Principal Aquifer. The site has been given a very low to high risk for the geological hazard of Ground Dissolution.

There are 21 contemporary trade directory entities within 250m of the site associated with a broad range of industrial uses.

Data Type On Site Within 250m

BGS Recorded Landfill Sites None Recorded None Recorded

Historical Landfill Sites None Recorded None Recorded

Licensed Waste Management Facilities (Landfill Boundaries)


Licensed Waste Management Facilities (Locations)


Registered Landfill Sites None Recorded None Recorded

Registered Waste Transfer Sites None Recorded None Recorded

Registered Waste Treatment or Disposal Sites


Table 4: Waste Summary Table


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3.1 Introduction

A Preliminary Conceptual Model has been derived to assess the risk (and likelihood) of the land being classified as “Contaminated Land” in accordance with Part IIA of the Environmental Protection Act.

In order for land to be deemed “Contaminated Land” a pollutant linkage is required between the following three variables;

A SOURCE (or hazard) - a contaminative substance that is present with the soil ( or groundwater) and has the potential to cause harm or pollution to a receptor.

A RECEPTOR - anything which can be effected by the SOURCE. E.g. groundwater, or end users.

A PATHWAY - a means to which the SOURCE can be linked to the RECEPTOR resulting in significant harm to the receptor.

Once a series of pollutant linkages (a source of contamination, via a pathway, to a receptor and a significant harm or a significant risk of a significant harm being caused by the effect of this pollutant linkage) have been established the probability and

consequence of this linkage being present or occurring is assessed and assigned a risk.

As both the consequence and probability of a pollutant linkage increases, the risk ultimately becomes more substantial and severe harm may be being caused to a sensitive receptor.

Tables 5 and 6 presented below detail the Environmental Risk Assessment Matrix used for the conceptual model and justifies the risk rating adopted for a given pollutant linkage.

3.2 Preliminary Conceptual Model

The following text lists the possible sources of contamination, pathways and receptors, as identified from the historical map, Envirocheck Report, Envirocheck Mining and Ground Stability Report and site walkover.

Possible Sources of Contamination

On-Site Sources:

Possible contamination from agricultural usage.

Section 3: Preliminary Conceptual Model

P

rob

ability

High Medium Low Negligible

High High High Medium / Low Negligible

Medium High Medium Low Negligible

Low High / Medium Medium / Low Low Negligible

Negligible Medium / Low Medium / Low Low Negligible

Consequence

Table 6: Risk Assessment Justification

Risk Definition

High Severe risk to a receptor being harmed or impacted. A source of contamination is probably or certainly present and is highly likely to have an unacceptable impact to a receptor.

Medium A receptor is likely to be impacted or harmed, however the consequence is unlikely to be severe. A source of contamination is probably or certainly present and may have an unacceptable impact to a receptor.

Low A receptor is unlikely likely to be impacted or harmed. Contaminants may be present but are unlikely to impact receptor.

Negligible No impact to a receptor and contaminants are unlikely to be present.

Table 5: Environmental Risk Assessment Matrix

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Off-Site Sources:

Possible contamination associated with Made Ground from adjacent developments, particularly on the western and south western boundaries of the site.

Possible soil gas from the underlying Chalk and infilled ground (Potential infilled Chalk Pit <10m to the north west).

Possible contamination from hydrocarbon fuel tank associated with haulage business at Gibraltar Farm.

Pathways (on or off the site):

Ingestion of soil and dust. (Pathway 1)

Dermal absorption. (Pathway 2)

Inhalation of dust and vapour. (Pathway 3)

Lateral and vertical migration of soluble contaminants as leachates on or off site. (Pathway 4)

Lateral and vertical migration of soil gas onto site. (Pathway 5)

Surface water runoff of soluble contaminants in soil and/or groundwater.

(Pathway 6)

Receptors

Humans (ground workers).

Humans (end users).

Soil.

Groundwater (Within Chalk Principal Aquifers).

Flora and Fauna.

All identified potential pollutant linkages are presented in the table 7 below.

Section 6: Preliminary Conceptual Model

Source Pathways Receptors Risk Justification for Risk Level

On site: Agricultural Usage 1,2,3,4,6 All Medium Potential contamination from pesticides and herbicide's from arable farming on site.

Off Site: Infilled Chalk Pit adjacent to Gibraltar Farm

3,4,5,6 Soil, Groundwater,

Flora and Fauna

Low Potential for contamination from material used for infilling. Potential gas from infillled

ground.

Off site: Made Ground from construction

1,2,3,4,6 All Low Construction occurred along western and south western boundary from circa 1970

Off Site: Soil Gas 5 Humans and Soil Low Chalk naturally produces carbon dioxide gas. Potential gas from infilled ground.

Off site: Above ground fuel tank

4, 6 All Low Potential hydrocarbon contamination from historic or current leakages.

Table 7: Preliminary Pollutant Linkages

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4.1 Scope of Works

The scope of the field work was specified by Create Consulting Engineers and undertaken by GTS in general accordance with Eurocode 7 Part 22, The Steering Group Specification (1993)6 and where there is no conflict BS 5930:19997. The soil descriptions used in the exploratory hole records are in broad accordance with the relevant European Standards3&4 and Section Six of BS 5930: 19997.

The prevailing ground conditions were determined by the following exploratory holes;

The location of the exploratory hole locations were provided on plans by Create Consulting engineers and set out by GTS on site, as indicated on the exploratory hole location plan presented in Appendix E. Before commencement of drilling and excavation, all exploratory positions were scanned using a cable avoidance tool (CAT). Within the borehole locations, a 1.20m deep hand excavated trial pit was completed to check for the presence of any near surface services prior to intrusive drilling. 4.2 Geotechnical Sampling Bulk disturbed and small disturbed samples were taken from the boreholes and trial pits to aid soil description and the productions of engineer verified logs.

4.3 Environmental Samples No environmental samples were taken as part of this investigation. 4.4 Machine Excavated Trial Pits with Soakaway Tests Nine machine excavated trial pits (SA1 to SA3 and TP4 to TP9) were dug by a JCB type excavator between the 14th and 15th April 2014, to depths between 2.25m and 4.30mbgl. The exposed strata were logged by an engineering geologist (Appendix A) from Ground Technology Services. Soakaway testing to BRE 365 was undertaken in three of the trial pits (SA1 to SA3). Water was then added to the trial pits on utilising a water pump and 500 gallon water bowser to allow rapid filling of the excavation. Once sufficient water was added to the trial pit, the monitoring of the water level commenced at regular time intervals in broad accordance with BRE Digest 3655. Three tests were completed in each test location . On completion of excavation and testing, the excavation was backfilled and compacted in layers and the area left as tidy as practicable after the completion of such works. The results of the soakaway tests are summarised in Appendix B. 4.5 Cable Percussion Boreholes Five cable percussion boreholes (BH1 to BH5) were each sunk to a depth of 20.00mbgl, utilising a Dando 2000 Rig. The boreholes were completed between the 21st May and 2nd June 2014. The bores were supported, where necessary, by the use of 200mm and 150mm diameter temporary steel casing. The recovered strata were recorded and disturbed samples taken during boring, as an aid to the production of borehole logs. The engineer verified logs are contained within Appendix A, and are based upon the descriptions of recovered samples. During the progression of the boreholes, constant head permeability tests were undertaken at depth

Section 4: Fieldwork

Hole Type Quantity

Cable Percussion Boreholes 5

Mechanically Excavated Trial Pits

5

Soakaway Test in Trial Pits to BRE 365

3

Table 8: Summary of Hole Types

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ranges specified by Create consulting Engineers, as outlined in Section 4.5.1 Following completion of drilling, sampling and permeability testing, the boreholes were backfilled with the spoil arising, and the area left as tidy as practicable after the execution of such works. 4.5.1 Constant Head Permeability Tests In each of the boreholes, two constant head permeability tests were undertaken. The depth the tests were carried out at were specified by Create Consulting Engineers Ltd (Create). The depths of the tests are recorded on the logs and also the test sheets for each test carried out, as shown in Appendix B. The boreholes were drilled to the maximum depth for the test to be carried out, and the test zone filled with gravel to prevent borehole collapse on withdrawing casing in unstable ground. At shallow depth. The casing was withdrawn after gravel installation to create a response zone between the base of the casing and bottom of the borehole. On creating the required test response zone, water was pumped into the borehole from a 2000 litre water bowser through a flow control system and water meter. On reaching a water level above the top of the response zone, the flow was reduced until a constant head was achieved in the borehole. This was sustained for a period of two minutes and the volume of water flowing into the borehole over this period recorded. Where a constant head was not achieved, the volume of water flowing into the borehole over the period of time to empty the water bowser was recorded, along with the maximum water depth from ground level achieved during filling. This typically occurred on all tests where the base of the response zone was 20m.

5.1 Physical Soil and Groundwater Conditions Five boreholes and nine trial pits were excavated primarily to provide information for the purposes of drainage characteristics for preliminary design. However, some general comments regarding the geology and comments regarding future geotechnical design and construction are provided below. Reference should be made to the appended exploratory hole logs for full details of the strata encountered by this investigation. However, as an aid to assessing the likely geotechnical properties of the materials encountered, four geological horizons have been distinguished. These are Topsoil, Clay With Flints Formation, Lewes Nodular Chalk Formation and the Seaford Chalk Formation. This is in general accordance with the geological information for the area1. 5.1.1 Topsoil Topsoil was encountered as a shallow surface covering in all exploratory holes to depths between 0.2m and 0.4mbgl. The Topsoil was generally cohesive soils comprising dark brown locally silty, sandy slightly gravelly to gravelly CLAY. Locally the deposit was described as clayey gravelly fine to medium SAND and sandy clayey SILT. The gravel fraction comprised angular to subangular fine to coarse flint. 5.1.2 Clay With Flints Formation Directly beneath the Topsoil, a stratum interpreted as Clay With Flints was encountered in all exploratory hole locations. With the exception of TP4 and TP6, these materials were encountered to depths ranging between 1.0m and 3.0m bgl. TP4 and TP6 were terminated within these materials at depths of 4.2m and 3.8m bgl, respectively. The Clay-with-Flints Formation is a residual deposit formed from the dissolution, decalcification and cryoturbation of bedrock strata of the Chalk Group and Palaeogene formations and, in the extreme west of the outcrop, the Upper Greensand Formation. It is

Section 4: Fieldwork Section 5: Ground Conditions

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chalk SILT matrix. The gravel comprised very weak to moderately weak angular fine to coarse intact chalk fragments. Flint cobbles were noted at localised depths throughout. In terms of classification, the chalk was recovered as a CIRIA Grade Dm CHALK, although cable percussive drilling does not provide adequate quality of samples for classification, owing to the high levels of disturbance during the drilling process. Better observations of the in-situ nature of the chalk were possible in the trial pit excavations. Within the trial pit exposures, the chalk was described as a structureless brownish white, light brownish white, creamy white or yellowish white CHALK, composed of very weak to weak angular to subangular fine to coarse chalk GRAVEL in a weathered chalk silt matrix, with occasional flint cobbles. The matrix accounted for no more than 30%, indicating CIRIA Grade Dc material.

Section 5: Ground Conditions

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6.1 General Comments Preliminary comments relating to the likely geotechnical and environmental risk the site is likely to pose, with regard to the proposed development, are provided in the following text. Comments are also provided with respect to further works recommended to provide sufficient information to mitigate the risks identified. Preliminary information supplied by Create Consulting Engineers, indicates that the site is to be developed with residential dwellings At the time of writing this report, the development is at an early stage of planning, and no design proposals are in place. As such the following comments are general in nature and will need verifying depending upon the final development proposals and need for further work. This document will form part of the planning submission for an outline planning application for up to 450 residential units based on the masterplan layout in Appendix E. 6.2 Environmental Considerations The site history has been reviewed, indicating the site has remained largely undeveloped, with the land use being arable farming and woodland. Some woodland clearance has been undertaken in favour of agricultural expansion, but no other changes have occurred within the site boundary. The surrounding area was predominately rural circa 1869, with large woodland areas and isolated dwellings and farms with a limited road network. Circa 1932, residential development began with the partial clearing of Lords Wood. The next phase of major development began in the 1970’s with residential and infrastructure development of Lords Wood, including the development of the M2 motorway to the south. The surrounding area received gradual residential and infrastructural development up to the present day. The Envirocheck Report has identified that there are no landfills, waste treatment facilities, discharge consents or contaminated land entries within 250m of the site. An area of non water infilled land is situated approximately <10m to the north west of the site.

The underlying soils are of intermediate to high leaching potential and the bedrock is a Principal Aquifer. The site has been given a very low to high risk for the geological hazard of Ground Dissolution. There are 21 contemporary trade directory entities within 250m of the site associated with a broad range of industrial uses. A preliminary conceptual site model has been developed, and indicates that the site is generally considered to be of low risk with respect to contamination and residential land use. However, due to the sites usage as arable farming, there is a moderate risk of herbicides and pesticides being present that warrants further investigation and assessment to determine the actual risk rating of this possible pollutant linkage. 6.3 Geotechnical Considerations The ground investigation has revealed the site to be underlain by a thin layer of Topsoil to depths between 0.20m and 0.40mbgl. This was underlain by predominantly cohesive but variable deposits of Clay With Flints, generally to no more than 3.0m, but locally deeper than 4.2m, overlying White Chalk, weathered to a structureless mass, most likely of CIRIA Grade Dc classification. The main purpose of the intrusive phases of investigation undertaken was to determine the likely drainage characteristics of the in-situ soils for the design and construction of shallow and deep soakaway drainage. However, preliminary comments regarding foundation and pavement design have also been provided at the request of the Engineer. 6.3.1 Soakaway Drainage Three trial pit soakaway tests to BRE 365 and ten constant head permeability tests in the boreholes were carried out. Table 9 provides a summary of the tests undertaken and the results obtained. Notably, infiltration rates were generally obtained in chalk strata. All trial pit permeability tests were undertaken in broad accordance with BRE Digest 365 and obtained results of between 7.04x 10-4 and 7.12 x 10-6 . The results indicate that the near surface Chalk soils have good drainage characteristics, and are likely to be sufficient for traditional soakaway drainage.

Section 6: Comments and Recommendation

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Section 6: Comments and Recommendation

Location Test Type Results Comments

SA1 Trial Pit Soakaway to BRE 365

Test 1— 4.68 x 10-4 m/sec

Test 2— 7.04 x 10-4 m/sec

Test 3— 6.82 x 10-4 m/sec

Water drained very quickly on filling. Only 0.37m to 0.46m head of water in pit at start

of test.


Test 1— 1.24 x 10-4 m/sec

Test 2— 7.12 x 10-5 m/sec

Test 3— 8.80 x 10-5 m/sec


of test.


Test 1— 2.00 x 10-4 m/sec

Test 2— 9.79 x 10-5 m/sec

Test 3— 9.14 x 10-5 m/sec


of test.

BH1 Constant Head Response Zone 1 3.0—4.5m

5.8 l/sec - 3.71 l/sec*

Response Zone 2 6.0—20.0m

2.68 l/sec*

Response Zone 1—unable to maintain flow sufficiently.

Response Zone 2—917 litres of water lost in 342 seconds during filling.


0.175 l/sec

Response Zone 2 4.5m—20.0m

5.56 l/sec*

Response Zone 2—Unable to fill quickly enough. 2000 litres of water lost in 360

seconds during filling.


5.15 l/sec*


5.59 l/sec*

Response Zone 1—.Unable to fill quickly enough. 1811 litres of water lost in 352


Response Zone 2—1947 litres of water lost in 348 seconds during filling.


2.43 l/sec


5.97 l/sec*

Response Zone 2—Unable to fill quickly enough.1929 litres of water lost in 323


BH5

Constant Head Response Zone 1 3.0—8.0m

3.12 l/sec


6.39 l/sec*

Response Zone 2—Unable to fill quickly enough.1912 litres of water lost in 299


Infiltration Strata

Chalk

Chalk

Chalk

Chalk

Chalk

Chalk

Chalk

Chalk

Chalk

Chalk

Chalk

Chalk

Chalk

Table 9: Summary of Soakaway and Permeability Test Results

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However, it should be noted that the initial water loss during filling was rapid, and the head of water achieved during the test varied between 0.37m and 0.83m. Additional tests using equipment capable of rapid filling should be considered before finalising any design in order to determine the values obtained are representative. Furthermore, it should also be noted that the shallow superficial deposits were noted to be of a cohesive nature, and as such are unlikely to be suitable for infiltration forms of sustainable urban drainage systems. With respect to the constant head tests in the boreholes, it should be noted that constant head was only achieved in three of the ten tests conducted. These were all in the shallow response zones in BH2, BH4 and BH5, which yielded results of 0.175 l/sec, 2.43 l/sec and 3.12 l/sec, respectively. All other tests did not achieve constant head, as the water during filling was entering the ground surrounding the borehole. In each of these tests, a full water bowser (2000 litres) was used. The flow rates in Table 9 marked with an * are based on the water lost during the duration of the filling time. The results of the incomplete tests indicate water loss rates in the range 2.68 to 6.39 l/sec, although were all between 5.31 l/sec and 6.39 l/sec with the exception of the low value. Care should be taken during design of any deeper borehole soakaway, as the volume of water used during the tests is much lower than a deep borehole soakaway would receive during a storm event. Scale effects mean increasing saturation of the ground with a full scale soakaway would decrease the rates of flow into the ground compared with the smaller scale test results. Care should be taken in selecting an appropriate value for design to take this into account. However, it would appear that deeper borehole soakaways would be feasible, depending on the calculated volumes of storm water to be discharged. Due to the presence of chalk beneath the site, and the moderate risk of dissolution feature development, care should be taken in selecting appropriate locations for any soakaway. While swallow holes rarely form surface depressions or voids of greater than 5m across, it is recommended that any soakaway is situated some 10m distant from any new construction and access road or other sensitive feature of the development. In addition, the use of permeable

paving should be considered to maintain drainage patterns into the ground beneath the site to as near natural conditions as possible. This will limit the possibility of dissolution problems being encountered during the design life of the development. However, the cohesive nature of the shallow superficial deposits should be taken into account. 6.3.2 Foundations Based on preliminary information, and the encountered ground conditions, shallow spread (trench fill) or pad footings are likely to be a feasible option in many locations on this site. Although clarification by further investigation would be required, allowable bearing capacities on Grade Dc chalk and firm to stiff to stiff clays are likely to be more than sufficient for traditional dwellings. However, deeper layers of firm clays were noted, which may offer insufficient bearing capacity and the compressibility of these materials may mean differential and/or total settlements may be too great. Changes in geology laterally, and depths to the chalk locally are also issues that will need to be determined by further investigation. Foundations spanning one soil type to another, and changes to the depth of geological horizons beneath footings increase the risk of differential settlement. At this stage, the requirement for piled foundations or some form of ground improvement cannot be ruled out in certain areas of the site. Furthermore, the moderate risk of solution feature development may also rule out shallow foundation systems and ground bearing floor slabs on the basis of the increased costs in terms of providing adequate reinforcement to span any voids opening up beneath the structures. 6.3.3 Road Pavement Design Based on the predominance of clay strata beneath the Topsoil, CBR values for preliminary design of 2% should be used. However, verification of this will be required in-situ testing prior to any final design being carried out. 6.3.4 Protection of Buried Concrete Recorded pH values have revealed the soil and groundwater samples tested to be between 7.7

Section 6: Comments and Recommendations

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and 8.9 indicating slightly alkaline conditions. The soil water soluble sulfate contents, are all within Class DS-1 of BRE1 (2005)9. Considering that the site is natural ground, with mobile groundwater, the site can be given an Aggressive Chemical Environment for Concrete classification of AC-1. Buried concrete can therefore be designed in accordance with minimum requirements of BRE classification. However, further site wide test should be carried out to ensure a sufficient sample size population to confirm this assessment.

7.1 Recommendations for Further Work On the basis of the desk study information and preliminary intrusive investigation, we would recommend the following additional works to address the environmental and geotechnical risks identified. 7.1.1 Geotechnical Three key geotechnical issues have been identified. Firstly the site overlies the Lewes Nodular Chalk Formation and the Seaford Chalk Formation (White Chalk Subgroup), which is overlain by the Clay with flints formation. The chalk subsidence risk assessment (section 2.5) identified a moderate risk. In addition, two known solution features are present south of the site. On this basis, we would recommend that any geotechnical investigations are undertaken on a close grid system, particularly within the southern area of the site. Should notable variations in density / strength be identified this may indicate the presence of solution feature activity, which will have an impact on future design and construction proposals. Secondly, the formations that comprise the White Chalk Subgroup is a natural source of carbon dioxide gas, consequently it is recommended that gas monitoring is completed within specially installed monitoring wells. Risk assessment in accordance with best practice guidance should be undertaken as part of the detailed design to inform the need for any ground gas protection measures. Thirdly, ground conditions vary across the site and additional information regarding this variation and also the strength and compressibility of these materials would be required for economic design.

In order to fully address the geotechnical risks present on this site, a full intrusive investigation will be required, which is likely to comprise the following; A series of shallow (2.00-4.00m) window

sample borehole to confirm geological variation across the site.

A series of deeper (15.00m) cable percussion boreholes to confirm soil strength profiles for foundation design.

A series of dynamic probes to confirm strength profiles and identify potential solution features / variation in chalk depth.

A series of machine excavated trial pits, with a number of soakaway tests (in accordance with BRE Digest 365) to assist with drainage design and confirm the tests already undertaken.

A series of California Bearing Ratio tests to confirm parameters for road pavement design

A series of geotechnical and chemical testing. 7.1.2 Environmental The intensive farming usage may have used herbicides, pesticides and fertiliser which may remain in the soil. While a general chemical testing suite of contaminants will also be required to confirm the suitability for use within the proposed residential development, it would also be essential to test for a broad range of potential agricultural contaminants prior to development to fully assess the risks to both groundwater and human health during and on completion of the development. In particular, the chemical suitability of the topsoil and near surface soils for re-use in landscaped areas should be confirmed in accordance with best practice guidance. In addition, while indicated as low risk, the Made Ground associated with developments adjacent to the site, an above ground fuel storage tank and the infilling of the former chalk pit to the north west will need to be investigated further by chemical testing of soil and groundwater. However, additional works associated with this would be expected to be minimal and would be undertaken to rule this out rather than to confirm the severity and risk of the presence of contamination. No special measures with respect to contamination are likely to be required to render this site suitable for the proposed development.

Section 7: Further Works

Section 7: Further Works Section 6: Comments and Recommendations

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1. British Geological Survey England and Wales, 1:50,000, (Solid & Drift Edition).

2. BS EN 1997-2 (2007): Eurocode 7 Geotechnical Design – Part 2: Ground Investigation and testing.

3. BS EN ISO 14688-1: (2002):Geotechnical Investigation and Testing – Identification and Classification of Soil – Part 1: Identification and Description.

4. BS EN ISO 14688-2: (2004):Geotechnical Investigation and Testing – Identification and Classification of Soil – Part 2: Principles for a classification.

5. BS EN ISO 14688-3: (2005):Geotechnical Investigation and Testing – Field Testing – Part 3: Standard Penetration Test

6. Specification for ground Investigation, Site Investigation Steering Group (1993).

7. BS5930: (1999) Site Investigation – Code of Practice, British Standards Institution.

8. BS1377: (1990) British Standard methods of test for Soils for Civil Engineering purposes, In-situ tests, British Standards Institution.

9. BOYLE, R and WITHERINGTON, P (2006). Guidance on evaluation on development proposals on sites where methane and carbon dioxide are present, incorporating ’traffic lights’. National House Building Council (NHBC).

10. Wilson S. et al (2006). Assessing Risks Posed by Hazardous Ground Gases to Buildings, CIRIA Project Report No C659.

11. BRE 1 (2005). Concrete in Aggressive Ground. Building Research Establishment Special Digest 1.

12. EDMONDS, C.N. (1987). The engineering geomorphology of Karst development and the prediction of subsidence risk upon the chalk outcrop of England. PhD thesis, University of London.

13. NHBC (1999). National House Building Council Standards, Chapter 4.2, Building near Trees.

14. LORD, J.A. et al. (1994). Foundations in Chalk, CIRIA Project Report No 11.

15. CLEA Using Soil Guideline Values (2009). The Environment Agency.

16. CLEA Human Health toxicological assessment of contaminants in soil (The TOX Guidance Report). The Environment Agency (2009).

17. CLEA Technical notes, Toxicological Reports & Supplementary information on available Soil Guideline Values (2009). The Environment Agency.

18. The CLEA report (2009). The Environment Agency. Updated technical Background to the CLEA model.

19. Contaminated Land Report 11 (CLR11) (2009). The Environment Agency. Model Procedures for the Management of Land Contamination.

20. CLEA Software Version 1.06 (2009) and Software Handbook.

21. BS10175: (2001) Investigation of Potentially Contaminated Sites – Code of Practice

Section 8: References

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22. RD20 (1999). The Environment Agency. Methodology for the Derivation of Remedial Targets for Soil and Groundwater to Protect Water Resources.

23. USEPA (1994). Technical Background Document for Soil Screening Guidance.

24. Water Supply (Water Quality) Regulations (2000).

25. EQS (2008). UK Technical Advisory Group on the Water Framework Directive (WFD). Proposals for Environmental Quality Standards (EQS) for Annex VIII substances.

26. EQS (2004). Department for Environment, Food and Rural Affairs (DEFRA) and The Environment Agency. Environmental Quality Standards.

27. Interim Advise Notice 73/06. Design Guidance for Road Pavement Foundations (2006)

28. The LQM/CIEH Generic Assessment Criteria for Human Health Risk Assessment (2nd Edn), 2009

29. BS7430: (1998) Code of Practice for Earthing, British Standards Institution.

30. Butcher A.P et al (1996) Dynamic Probing and its uses in clay soils. Advances in site investigation practices.

31. Cearns, P.J and McKenzie, A (1988) Application of dynamic cone penetrometer test in East Anglia, Thomas Telford, London

Section 8: References

Land at Gibraltar Way, Chatham Surface Water Management Strategy

Appendices

Appendix A.3 – Indicative Drainage Layout Plan

Appendix A.2 – Site Investigation Results

Documents

Transcript of Appendix A.2 – Site Investigation Results