Former Bayer Crop Science Site Hauxton Cambridgeshire June

Vertase F.L.I. Limited3000 Aviator WayManchester Business ParkManchester M22 5TG

Tel +44 (0) 161 437 2708Fax +44 (0) 161 437 6300

Email [email protected]

Further Quantitative Risk Assessment for Controlled Waters and Preliminary Post-Remediation Validation Model

Former Bayer Crop Science SiteHauxtonCambridgeshire

June 2011

On behalf of:

Harrow Estates Plc

Executive Summary The report has been prepared to reassess the risk assessment with respect to controlled waters at the former BayerScience site, Hauxton following the collection of further data during the ongoing remediation. This report describes the site setting and outlines previous work undertaken to date with respect to the controlled waters risk assessment. It takes on board information gathered during the current remedial works and builds upon previous investigation data to provide a revised conceptual site model for the post remediation conditions that has significantly more certainty with regard to volumes and types of soil material and thus the geometry of restored soil horizons compared to previous models. This assessment follows the previous risk assessment (Further Quantitative Risk Assessment for Risks to Groundwater and Surface Water, Former Bayer Crop Science Site, Hauxton, Cambridgeshire February 2011) and has been adapted to the new post remediation conceptual site model for and expanded to cover all contaminants of concern. This is now a major step towards the final post remediation risk assessment model that was discussed in the remediation method statement. This assessment will now be updated on a continual and ongoing basis with site data from the ongoing validation. An appropriate level of conservatism and variation within parameters has been built in to allow for any future variability in the treated soils at site. Geotechnical and hydrogeolgical parameters for the treated soils have been assessed through laboratory and in-situ testing. These site specific parameters have subsequently been used in the risk assessment model to enable the potential risks from any residual contaminants in the reinstated remediated soils to be assessed. The output from the model represents the maximum concentrations in soils and leachate that would not result in an exceedance of the selected compliance target at the receptor, the Riddy Brook (i.e. the Environment Agency Environmental Quality Standards or equivalent.) These maximum concentrations will be used as such and in most cases material will be treated much below these concentrations to ensure that the risks are minimised further. The actual achieved concentrations post treatment so far can be as much as several orders of magnitude lower than these maximum concentrations. In order to be protective of human health also a set of ‘working targets’ has been prepared to ensure remediated soils are both acceptable within the controlled waters risk assessment and that of human health. These are presented in separate documents. We will now continue to build on this model and will add further data to the model as we continue to progress with validation and restoration of material. Once material is restored at the site we wil have final residual contaminants of concern concentrations in the reinstated soil materials, updated geotechnical and hydrogeological parameters and fraction organic carbon which will be entered into the models as probability density functions (or PDF’s) to represent actual material at the site. The model will be ‘re-run’ periodically to ensure that no risk to controlled waters remain resulting ultimately in a post remediation model accurately reflecting ground conditions at the site.


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Table of Contents

1.0 Introduction .......................................................................................................................................... 1

1.1 Limitations ..................................................................................................................................... 1

2.0 Remediation Strategy and Approach to Risk Assessment ............................................................... 2

3.0 Environmental Setting ......................................................................................................................... 4

3.1 Site Description.............................................................................................................................. 4

3.2 Pre Remediation Conditions .......................................................................................................... 4 3.2.1 Pre-Remediation Ground Conditions..................................................................................... 4 3.2.2 Existing Remedial Measures ................................................................................................. 5 3.2.3 Hydrogeology ........................................................................................................................ 5 3.2.4 Hydrology.............................................................................................................................. 7

3.3 Observed Conditions During Remedial Works............................................................................... 7 3.3.1 Ground Conditions ................................................................................................................ 7 3.3.2 Additional Contaminant Source ............................................................................................. 7 3.3.3 Hydrogeology ........................................................................................................................ 8

4.0 Review of Previous Reports ................................................................................................................ 9

4.1 Enviros Consulting ‘Part IIA Site Investigation Report’ for Bayer Crop Science, January 2005...... 9

4.2 Atkins Environment, ‘Remediation of Former Bayer Site, Hauxton, Preliminary Conceptual Model Report’ August 2006................................................................................................................................. 10

4.3 Atkins Environment, ‘Former Bayer Site, Hauxton, Groundwater Modelling Report’, June 2007.. 11 4.3.1 MODFLOW ......................................................................................................................... 12 4.3.2 QRA .................................................................................................................................... 13

4.4 Vertase FLI, Further Quantitative Risk Assessment for Risks to Groundwater and Surface Waters, January 2011............................................................................................................................................ 15

4.5 Summary of Previous Works ....................................................................................................... 15

5.0 Conceptual Site Model....................................................................................................................... 16

5.1 Original CSM ............................................................................................................................... 16

5.2 Post Remediation Site Conditions................................................................................................ 16 5.2.1 Ground Conditions .............................................................................................................. 16 5.2.2 Groundwater Flow Through the Site.................................................................................... 18 5.2.3 Aquifer Parameters ............................................................................................................. 20

5.3 Post Remediation CSM................................................................................................................ 21 5.3.1 Contaminant Source............................................................................................................ 21 5.3.2 Pathways ............................................................................................................................ 22 5.3.3 Receptor ............................................................................................................................. 22

6.0 Selection of Risk Assessment Software and Modelling Approach ................................................ 23

6.1 Environment Agency Remedial Targets Methodology ................................................................. 23 6.1.1 Assessment of Risks from Soils .......................................................................................... 23 6.1.2 Assessment of Risks from Contaminated Groundwater ...................................................... 23 6.1.3 Conceptual Model ............................................................................................................... 24

6.2 Comparison of EA RTM and Site Conceptual Site Model ............................................................ 24

6.3 Risk Assessment Approach ......................................................................................................... 24 6.3.1 Applicability of EA RTM Risk Assessment Levels ............................................................... 24 6.3.2 Selection of Modelling Software .......................................................................................... 25 6.3.3 Assessing Risks from Type B and C Soil Material ............................................................... 26 6.3.4 Assessing Risks from Type A Soil Material ......................................................................... 27


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7.0 Model Inputs ....................................................................................................................................... 29

7.1 Contaminant Sources .................................................................................................................. 29

7.2 Receptors .................................................................................................................................... 30

7.3 Selection of Screening Criteria .................................................................................................... 30

7.4 Selection of Aquifer Pathway Parameters – Level 3a Assessment .............................................. 31 7.4.1 Aquifer Thickness................................................................................................................ 32 7.4.2 Dry Bulk Density.................................................................................................................. 32 7.4.3 Mixing Zone Thickness........................................................................................................ 32 7.4.4 Hydraulic Conductivity......................................................................................................... 32 7.4.5 Effective Porosity ................................................................................................................ 33 7.4.6 Hydraulic Gradient............................................................................................................... 33 7.4.7 Groundwater Flow Direction ................................................................................................ 33 7.4.8 Dispersivity.......................................................................................................................... 34 7.4.9 Fraction of Organic Carbon ................................................................................................. 34 7.4.10 Summary............................................................................................................................. 34 7.4.11 Model Settings .................................................................................................................... 35 7.4.12 Model Correlations .............................................................................................................. 35

7.5 Soil Source Parameters – Level 1 Assessment ........................................................................... 35

7.6 Contaminant Parameters ............................................................................................................. 37 7.6.1 Selection of Parameters ...................................................................................................... 41

8.0 Model Outputs .................................................................................................................................... 42

8.1 Leachate/Groundwater Maximum CoC Threshold Values ........................................................... 42

8.2 Soil Maximum CoC Threshold Values ......................................................................................... 43 8.2.1 Comparison of Leachate and Soil CoC concentrations ....................................................... 43 8.2.2 ConSim Level 1 Assessment............................................................................................... 44 8.2.3 Comparison of Soil Threshold Values ................................................................................. 45

9.0 Summary............................................................................................................................................. 47

9.1 Further Work................................................................................................................................ 47


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Appendices

Appendix A Vertase FLI Drawings

Drawing D907_87 – Surveyed Geological Section

Drawing D907_154 –Post Remediation Conceptual Site Model

Drawing D907_134 - ConSim Graphical Input of Source Zones and Receptor, Type B and C model

Drawing D907_169 – ConSim Graphical Input of Source Zones and Receptor, Type A model

Appendix B Atkins Drawings

Drawing 5036759/002, Conceptual Site Model for Proposed

Site Development, July 2006

Drawing 5036759/Figure 5, Groundwater Contours (mAOD)

April 29th 2006


May 11 to 16th 2006


16th December 2006

Appendix C Water Pumping Volumes

Appendix D Geotechnical Results

Appendix E Soil Source Parameter Supporting Data

Fraction of Organic Carbon

Moisture Content

Appendix F Contaminant of Concern – Input Value Justifications

Appendix G Contaminants of Concern – Literature Values

Appendix H ConSim Model Inputs – Type A Material

Appendix I ConSim Model Inputs – Type B and C Material

Appendix J Relationship Between Soil and Leachate CoC


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Concentrations

Appendix K Data CD

ConSim Model Outputs


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1.0 Introduction

VertaseFLI have been appointed by Harrow Estates Plc to undertake remedial works at the

former Bayer Crop Science agrochemicals works in Hauxton, Cambridgeshire (the site).

The site has been determined as a Special Site under Part IIa of the Environmental

Protection Act (EPA) 1990 due to identified significant pollutant linkages being present with

respect to groundwater and surface water resulting from the former use in the production

and storage of agrochemicals.

The majority of the buildings and structures at the site have been demolished, and at the

time of writing, remedial works comprising the excavation of contaminated soil material, the

formation of biopiles (including the addition of organic matter) and turning of the

contaminated soil material were being undertaken. On completion the remediated soils will

be reinstated at the site and the site will be developed for primarily residential use.

In order for the remediated soil material to be reinstated, it must be demonstrated through

the development of an appropriately detailed risk assessment, that the reinstated soils do

not present a significant risk to local receptors such as groundwater and surface water. The

initial risk assessment and remedial targets were based on site investigation data collected

prior to remediation. As the remedial works have progressed, more data has been obtained

on the volumes and properties of the different soil material present at the site so that a more

detailed and representative post remedial conceptual site model can be developed.

Therefore, in accordance with the remediation method statement (VertaseFLI, Apr 2010)

this report reassesses and where necessary revises the risk assessment for the site in light

of the additional data collected during the remedial works.

1.1 Limitations

It is important to note that this document refers to the CSM with respect to the controlled

waters risk assessment only. A human health risk assessment has been undertaken and

presented in the report, Derivation of Pesticide Soil Screening Values & Evaluation of the

Spatial Extent of Contamination (Atkins, July 2007). It is also discussed in the VertaseFLI

Remediation Strategy Report (VertaseFLI, Nov 2008).


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2.0 Remediation Strategy and Approach to Risk Assessment

The main strategy for the remediation at the site was to excavate all materials at the site to

ensure that all uncertainty regarding contaminants and geological conditions are removed.

All excavated soil material was to be segregated, classified and treated as appropriate

before being reinstated and validated. Any contaminated groundwater was to be

separated, treated and disposed from the site under discharge consent. Following the

remediation and reinstatement of soils, a clean cover system will be imported from off-site

above the finished levels.

Paragraphs 6.3 and 6.4 of the Remediation Strategy set out the approach to be used in

developing the risk assessment with respect to environmental receptors as follows:

6.3 An important part of the approach of our remedial strategy will be to collect

further information on the geology, hydrogeology, contamination, material

parameters and characteristics during the remedial works. It is our intention

that this information will be used to further develop the site model to re-

evaluate the remediation targets. This will be continually re-assessed as the

remediation is continued and may ultimately result in the preparation of a

numerical model that represents exact site conditions with a high degree of

certainty to prove that materials present on site post remediation do not

represent a significant risk of significant harm to the environment and that

adequate remediation works have been completed to satisfy the

requirements under Part IIa of the Environmental Protection Act 1990.

6.4 This modelling approach will be calibrated by site based monitoring and the

mode calibrated appropriately. It does mean that some material will be

replaced at the site that does not meet the present generic criteria but

through the remediation we will have detailed data and knowledge of this

material which will allow clearer understanding of the site. This knowledge

and understanding will be used to present a new conceptual model and

appropriate risk assessment.

Therefore, an iterative approach has been used to allow the groundwater risk assessment

to be further developed as more data becomes available during the risk assessment, so

that the post remediation site conditions and conceptual model, and therefore the site

specific remedial targets, can be developed with as much accuracy as possible. The level


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of data now available has enabled a robust model for all contaminants of concern to be

developed with revised risk based remediation targets to work towards. As the remedial

work continues and soil material is reinstated, the validation data for the reinstated soils will

be incorporated into the risk assessment model as part of the validation process so that on

completion of the work the final model will accurately represent the remediated conditions at

the site.


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3.0 Environmental Setting

3.1 Site Description

The site is situated approximately 200 m northwest of the village of Hauxton (National Grid

Ref TL 432524), and covers an area of approximately 9 hectares. It was previously

occupied by Bayer CropScience and used for the production and storage of agrochemicals

including pesticides, insecticides and herbicides.

The site is bounded to the west by the A10 trunk road beyond which is agricultural land and

the Waste Water Treatment Plant (WWTP) for the Site. The northern and eastern site

boundaries are formed by the Riddy Brook, with Church Road forming the southern site

boundary and the southeast of the site bounded by agricultural land.

The site is generally level with a ground elevation of between 12 and 13 m AOD.

3.2 Pre Remediation Conditions

3.2.1 Pre-Remediation Ground Conditions

Based on the information provided by Enviros (2005) and Atkins (2006), the pre-

remediation ground conditions at the site are presented in Table 1.

Table 1: Ground Conditions

Description Thickness

Made Ground (consisting of reworked sand and gravel, chalk marl, alluvium, brick rubble and clinker), foundations, drainage features and voids

Typically up to 2 m bgl, with a maximum thickness of 5 m

Superficial Deposits – Alluvium and River Terrace Gravels

Generally < 3 m thick where present. Completely replaced by Made Ground in parts of the site

West Melbury Marly Chalk Formation (WMMCF) – Marly chalk with thin limestone bands, typically described in available logs as a stiff light grey clay

Present in the south and northwest of the Site only. Typically less than 3m thick with a maximum thickness of 7m in some areas.

Gault Clay

Typically present at a depth of 5 m bgl underlying Made Ground/Superficial Deposits/WMMCF, the thickness is understood to be up to 50 m (based on historic borehole data presented in Atkins (2006)


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Lower Greensand 15 – 20 m

3.2.2 Existing Remedial Measures

Prior to the current remedial works at the site, the following measures had been undertaken

at the site to control groundwater:

A bentonite and cement cut-off wall was constructed along the Riddy Brook. It is

understood to have been installed in 1974;

A groundwater abstraction system was in use in the north of the site to prevent the

migration of contaminated groundwater to the north of the bentonite wall. The

system comprised several sumps which were pumped to the waste water treatment

works (WWTW) to the north of the site; and

A dewatering system was present in the south of the site associated with the

warehousing in this area. The construction of the warehouse and associated

loading areas is understood to have included the excavation of soil material such

that they were constructed below the natural water level on the site. As a result, a

dewatering system comprising a sump was constructed to artificially lower the

groundwater level in this area with all waste water pumped to the adjacent WWTW.

3.2.3 Hydrogeology

3.2.3.1 Geological Units

Made Ground and Drift Deposits

The natural drift deposits at the site comprise River Terrace Gravels and Alluvium and are

classified by the Environment Agency as a Secondary A Aquifer which are described as:

‘permeable layers capable of supporting water supplies at a local rather than

strategic scale, and in some cases forming an important source of base flow to

rivers. These are generally aquifers formerly classified as minor aquifers.’

The granular Made Ground was considered by Atkins to be part of the same hydraulic units

for modelling purposes. The presence of cohesive Made Ground was considered to be

associated with the presence of perched groundwater.


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West Melbury Marly Chalk Formation

The Lower Chalk (which includes the WMMCF) is classified by the Environment Agency as

a Primary Aquifer. A Primary Aquifer is described as:

‘These are layers of rock or drift 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. In most cases,

principal aquifers are aquifers previously designated as major aquifer.’

However, the investigations undertaken by Enviros and Atkins indicated that the WMMCF

was largely absent from the centre and north of the main site. The WMMCF had a high

content (typically described in available borehole logs as a stiff light grey clay) and was

considered by Atkins to have poor aquifer properties

Gault Clay

The underlying Gault Clay is considered to act as an aquiclude, preventing continuity

between any shallow groundwater present in on the site and the Lower Greensand which

underlies the Gault.

3.2.3.2 Groundwater Levels and Flow Direction

Groundwater was typically present at depths between 0.69 and 2.42 m below ground level

(bgl) with an average depth on the site of 1.3 m bgl. Based on the available site

investigation data, pre remediation, groundwater flow was assumed to occur within the

granular Made Ground and drift deposits, site infrastructure, and within the dis-continuous

sand and gravel lenses within the underlying WMMCF.

The local groundwater flow direction was generally from the south and west towards the

Riddy Brook and the River Cam. However, groundwater flows on site were significantly

altered due to the presence of a bentonite cut off wall along the northeast site boundary and

the ongoing abstraction of groundwater in both the north and the south of the site. As can

be seen from the 2006 Atkins groundwater contours presented in Appendix B, a

groundwater low was present in the south of the site as a result of the

dewatering/groundwater abstraction in this area which resulted in groundwater flow towards

this area and a steeper hydraulic gradient over much of the site compared to off-site.

Following remediation including the removal of the bentonite wall and cessation of

groundwater abstraction, it is anticipated that groundwater flow across the site will generally

be to the northeast, towards the Riddy Brook.


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3.2.4 Hydrology

The Riddy Brook and Hauxton Mill Race are the closest water bodies to the site, forming

much of the northern and eastern site boundary. The Riddy Brook and Hauxton Mill race

meet immediately to the north of the site where they enter the River Cam. Shallow

groundwater at the site is considered to be in direct continuity with the Riddy Brook.

Due to the existing bentonite wall and groundwater abstraction system, the site does not

currently contribute significantly to the Riddy Brook base flow.

3.3 Observed Conditions During Remedial Works

As the remediation has progressed, the excavation of soil material across the site has

allowed a far more detailed understanding of the pre-remediation ground conditions

including the extent of contamination, and the hydrogeological properties of the soil material

to be developed. The following sections describe the additional observations made during

the remediation of the site so far.

3.3.1 Ground Conditions

The excavation of soil material as part of the remedial works has generally confirmed the

distribution and thickness of the Made Ground, WMMCF and Gault Clay described by

Enviros and Atkins.

The presence of natural superficial deposits typically comprising sand and gravel was also

confirmed. The excavations showed the deposits to have been discontinuous across the

site, as described in the previous site investigations, and comprised several large shallow

lenses of sand and gravel with a maximum thickness of 3m.

Thin discontinuous lenses of sand and gravel were also identified in the WMMCF. Drawing

907_85 in Appendix 1 shows a surveyed section of the excavation with exposed isolated

sand and gravel lenses present within the surrounding stiff grey clay material.

It is important to note, that post remediation, the ground conditions and properties may be

significantly different to the pre-remediation conditions due to the homogenisation of soil

material during the remediation and the compaction on reinstatement.

3.3.2 Additional Contaminant Source

The excavations generally confirmed the contaminant distribution identified in the previous

reports with contaminant levels generally highest in the former process areas. However,

during the excavations a discreet lens of sand and gravel in the top of the WMMCF was

identified to the northeast of the site (surveyed on Drawing 907_85), adjacent to the Riddy


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Brook which also contained between 20 and 30 corroded steel drums. The sand and gravel

was associated with significantly elevated contaminant concentrations. The sand and gravel

lens extended to the Riddy Brook and may have acted as a direct contaminant pathway

until the bentonite wall was constructed,

On discovery, the drums were appropriately disposed of and the associate sand and gravel

moved to a treatment bed.

3.3.3 Hydrogeology

Prior to remediation, groundwater flow to the Riddy Brook through the site was assumed to

be through granular Made Ground and granular drift deposits with the majority of any flow

through the discontinuous lenses of sand and gravel within the WMMCF as shown in the

original Atkins CSM (Appendix B).

However, as described in 3.2.1 and 3.3.1, the WMMCF predominantly comprises stiff clay

with thin isolated discontinuous lenses of sand and gravel. The full thickness of WMMCF

has been exposed in the sides of the remediation excavations. Based on the exposed

sections, groundwater flow within the in-situ WMMCF surrounding the site is very low with

any flow generally occurring as seepages through the discontinuous sand and gravel

lenses. These seepages through the exposed lenses typically decrease with time

suggesting negligible recharge through natural strata as would be expected given the

discontinuous nature of the sand and gravel lenses and the surrounding stiff clay/marl. As a

result, the excavations which are to depths significantly below the natural water table over

much of the site, have largely remained dry (with the exception of rainfall) for the duration of

the remediation so far.

In areas where excavations have not commenced groundwater flow appears to be largely

associated with the presence of drainage features and other site infrastructure, and the

presence of granular Made Ground following periods of rainfall.

The pumping system in the north of the site is no longer in use. The remaining pumping

system in the south of the site receives all water from the site drainage system. The sump

for the pumping system is located adjacent to a lens of sand and gravel and this is likely to

contribute to the total volume of water removed from the site.


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4.0 Review of Previous Reports

A number of investigations and risk assessments have been undertaken at the site since

1991. For clarity, a summary is provided in the following sections of some of the previous

work carried out.

The following reports relevant to the assessment of risks to groundwater and surface waters

were made available to VertaseFLI for review:

Enviros Consulting Ltd, ‘Part IIA Site Investigation Report, Report for Bayer Crop

Science’, January 2005, Reference SH0250008A;

Atkins Environment, ‘Remediation of Former Bayer Site, Hauxton, Preliminary

Conceptual Model Report’ Prepared for Bridgemere UK Limited and Harrow Estates

Plc, August 2006;

Atkins Environment, ‘Former Bayer Site, Hauxton, Groundwater Modelling Report’,

Prepared for Harrow Estates Plc, June 2007; and

Vertase FLI, ‘Former Bayer Crop Science Site, Hauxton – Further Quantitative Risk

Assessment for Risks to Groundwater and Surface Waters’, February 2011, 907BRI

Rev A.

In accordance with the Remediation Strategy, a review of the previous site investigations

and risk assessments was undertaken. The principal findings of previous investigations and

risk assessments at the site are detailed in the following sections.

4.1 Enviros Consulting ‘Part IIA Site Investigation Report’ for Bayer Crop Science,

January 2005

The report details the findings of the site investigation undertaken to satisfy the

determination of the site as a Special Site under Part IIa of the Environmental Protection

Act 1990. The report built on previous work at the site from 1991 onwards which had

included installation and monitoring of 59 No. piezometers and 19 No. monitoring

boreholes. Additional intrusive work comprised the drilling of 10 No. new boreholes and 41

window sample holes. The key findings of the report were:

Identified soil contamination was largely restricted to localised hot spots within the

site, typically in the immediate vicinity of the former production areas. Identified

contaminants included a wide range of pesticides and VOCs;


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Soil contamination was considered to make a small and localised contribution to the

contaminant source with only small volumes of contaminated soil identified in the

unsaturated zone. It was considered that greatest potential impact on controlled

water receptors would be from the presence of contaminants within groundwater;

The greatest concentration of contaminants in groundwater was identified in the

centre of the site;

Contaminant concentrations in groundwater were significantly lower outside of the

identified contaminant source areas. The decrease in concentrations was much

greater than would be anticipated through contaminant migration alone and it was

therefore considered that biodegradation of contaminants was occurring.

Additionally, one of the main solvent contaminants in groundwater at the site was

trichloroethene (TCE) and the presence in groundwater of breakdown products

which increased as TCE decreased away from the source was taken as further

evidence of biodegradation occurring;

The WMMCF was proven to be absent under much of the site and less than 4m

thick downstream of the contaminant sources. The WMMCF was also of low

permeability. Therefore, the WMMCF was not considered to be a significant receptor

and the potential pollutant linkage between the site and the WMMCF was

considered invalid; and

A significant pollutant linkage was confirmed between contaminated shallow

groundwater and the Riddy Brook and River Cam.

4.2 Atkins Environment, ‘Remediation of Former Bayer Site, Hauxton, Preliminary

Conceptual Model Report’ August 2006

Atkins Environmental (Atkins) prepared the report on behalf of Harrow Estates to further

develop and refine the conceptual site model (CSM) for the site and to address

uncertainties identified in the Enviros report. An additional 12 boreholes and 17 window

sample holes were drilled over the site to further assess the ground conditions overlying the

Gault Clay and to install new groundwater monitoring boreholes. Samples of soil and

groundwater were analysed for contaminants including individual pesticides and herbicides,

some geotechnical testing was also undertaken and, falling head tests were conducted

between 1.5 m and 3.6 m bgl during drilling.

The principal findings of the work were:


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The investigations confirmed the highest contaminant concentrations were in the

former production and storage areas of the site;

Leachate analysis indicated that there was the potential for contaminants, including

pesticides and herbicides to leach into groundwater at the site;

Groundwater analysis identified high levels of pesticides and organic substances

although there did not appear to be a consistent pattern of groundwater

contamination, transport or migration across the site, with the presence of cohesive

soil material appearing to limit migration;

Concentrations of light non aqueous phase liquids (LNAPL) and dense non-aqueous

phase liquids (DNAPL) were identified in concentrations that may have been

indicative of free phase contaminants to be present;

The report confirmed the Enviros findings that biodegradation of pesticides,

herbicides and organic compounds was occurring;

The report considered that both the WMMCF and surface water courses (Riddy

Brook and the River Cam) should be considered as receptors; and

The report recommended the use of the use of MODFLOW and the Environment

Agency Remedial Targets Worksheet to derive suitable remedial targets for the

site.

4.3 Atkins Environment, ‘Former Bayer Site, Hauxton, Groundwater Modelling

Report’, June 2007

Based on the findings of the Preliminary CSM report (discussed in Section 4.2), a

quantitative risk assessment (QRA) was conducted using MODFLOW and the Environment

Agency Remedial Targets Worksheet (EA RTW). Additionally, further assessment of the

presence of DNAPL was carried out and pumping tests were also undertaken to provide

more information on the hydraulic conductivity in the soil material overlying the Gault Clay.

The approach taken for the groundwater modelling for the QRA was as follows:

Development of a detailed water balance for the site and surrounding catchment

area;


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The development of the MODFLOW model based on the local geography, geology

and hydrogeology which was calibrated based on observed groundwater levels and

hydraulic conductivities from the site investigation data;

The calibrated MODFLOW model was used to plot travel pathways and the relative

unretarded travel times between known contaminant sources and the controlled

water receptor (the Riddy Brook) using MODPATH;

Qualitative risk screening was conducted based on contaminant concentrations,

distance and travel time to receptor and the retardation characteristics of individual

contaminants to select a representative list of priority contaminants at the site; and

Quantitative Risk Assessment of the priority contaminants was using the EA

Remedial Targets Worksheet (EA RTW) which set the preliminary remedial targets.

4.3.1 MODFLOW

The modelled catchment which included the site covered an area of 213.9 ha. A water

balance calculation was undertaken for the catchment area based upon the estimated

groundwater base flow to the River Cam and predicted infiltration rates for grassland. This

gave an infiltration rate of 1.45 x 10-4 m/day which was used to derive a total water balance

for the catchment of 310 m3/day.

A groundwater flow model for the site was developed using MODFLOW. An iterative

approach was taken in the development of the model with input parameters being refined to

reflect observed site conditions and data obtained from the site investigation such as the

hydraulic conductivities obtained from the pumping tests. A total of 20 models were run to

develop the final model of the site which included the modelling of the bentonite wall and

groundwater abstraction which was ongoing at the time of writing.

Two additional models were also run for the proposed redevelopment of the site with the

groundwater abstraction and bentonite wall removed from the model although it was not

clear if any other groundwater parameters were altered to reflect the likely changed in

groundwater flow. Uniform infiltration rates of 0.0001 m/d for residential properties and

0.00001 m/d for commercial properties were assumed, the modelling conducted with a

uniform distribution between the two values. It was considered that the models gave a

reasonable representation of the likely future groundwater flux rates and therefore the

hydraulic conductivity and hydraulic gradients developed for the models were considered

appropriate to use in the QRA.


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4.3.2 QRA

The QRA used the EA RTW to model the potential risks. UK Drinking Water Standards

were used as appropriate target criteria for the risk assessment due to the limited number of

Environment Agency Fresh Water Environmental Quality Standards (EQS) available for

organic compounds.

The site was divided into two zones which were modelled separately. The first zone

comprised the area within 20 m of the Riddy Brook (the receptor) with the second zone

comprising the remainder of the site. Twenty three contaminants of concern (CoC) were

identified and remedial targets were developed for all CoCs in both zones. However, there

were recognised issues with assessing the cumulative impact on the Riddy Brook from two

separate sources. As a result for the outer zone, remedial targets were derived based on

90% of the modelled remedial target assuming a distance of 60 m to the receptor. For the

inner zone, the distance to receptor was assumed to be 1 m.

4.3.2.1 Aquifer Parameters

The modelled aquifer was the Made Ground, and the inputs for bulk density and porosity

were based on assumed values for cohesive and granular soils. The hydraulic conductivity

and hydraulic gradient were determined through the MODFLOW analysis. Typically, for

each parameter a range of values was obtained and a representative distribution

(Probability Distribution Function (PDF)) selected so that the natural variability of the aquifer

could be represented. The aquifer parameters used in the model are presented in Table 2.

Table 2 – Aquifer Properties Used in Atkins QRA

Parameter Units PDF Minimum Most Likely Maximum

Water filled soil porosity % Triangular 2 10 30

Effective Aquifer Porosity % Triangular 2 10 30

Air Filled Porosity % Uniform 1 - 2

Bulk Density of soil material in aquifer

gcm-3 Uniform 1.05 - 2

Infiltration rate m/day Uniform 1x10-5 - 1 x 10-4

Hydraulic Conductivity m/day Log

Triangular 0.01 0.1

1.0

Hydraulic Gradient m/m Triangular 0.01 0.08 0.13


14 Rev A 907BRI

4.3.2.2 Contaminant Parameters

Contaminant parameters (Kd, Henrys Law Constant and half-life in groundwater) were

obtained from literature values, primarily obtained from the following references:

‘Handbook of Physical-Chemical Properties and Environmental Fate for Organic

Chemicals’ Second Edition, Mackay et al;

ToxNet: The United States Natural Library of Medicine, Hazardous Substances Data

Bank – http://toxnet.nlm.nih.gov;

EEC active substance reports –

http://ec.europa.eu/food/plants/protection/evaluation/exist_subs_rep_en.htm; and

Relevant Environment Agency publications.

A representative range of values and PDF was selected for each contaminant parameter.

Values of partition coefficient Kd were calculated based on literature values of the soil

organic carbon partition Coefficient Koc and averaged site specific values for the fraction of

organic carbon (FOC) using the equation Kd = Koc x FOC. As an additional factor of safety,

10% of the calculated value of Kd for each contaminant was used to develop the remedial

targets.

For several pesticides and herbicides, there were no published values for contaminant half

life in water. In these cases, a range of half lives considered by Atkins to be conservative

(relative to modern pesticides) were used in the model, typically 100 to 730 days.

4.3.2.3 Selection of Input Values

The EA RTW requires single inputs for each aquifer and contaminant parameter. However,

as detailed above, the aquifer and contaminant properties comprised a range of values and

representative PDFs. Therefore, the predictive modelling software Crystal BallTM was used

with the parameter ranges and PDFs to derive a single value based on the 95th percentile

value for each parameter.

4.3.2.4 Remedial Targets

Remedial targets were developed for soil and groundwater in both the inner and outer

zones of the site. A number of the calculated remedial targets were below the commercially

available limits of detection, and for these contaminants the remedial targets were set at the

detection limit.


15 Rev A 907BRI

4.4 Vertase FLI, Further Quantitative Risk Assessment for Risks to Groundwater

and Surface Waters, January 2011

The report reassessed the remedial targets for five priority contaminants of concern

(dicamba, schradan, Bis(2-chloroethyl)ether, ethofumesate and 1,2-dichloroethane) using

ConSim. ConSim was selected as a suitable risk assessment tool as it can assess the

combined effects of different contaminant sources at a receptor and it allowed a range of

input values (in the form of probability functions) for all parameters using Monte-Carlo

analysis so that natural variations in inputs can be modelled to produce 95th percentile

probability.

Due to the geometry of the site, for the modelling, the site was divided into four zones, Zone

1 (the 20 m buffer zone), Zone 2S and 2N (in the centre of the site) and Zone 3 in the

southwest. For consistency, and where appropriate, inputs from the Atkins RTW model

were used. Soil material was divided into three types, Type A (Granular Made Ground and

sand and gravel), Type B (WMMCF) and Type C (Gault Clay).

Environment Agency EQS values for freshwater were used for screening criteria at the

Riddy Brook, or if not available UK drinking water standards. If neither was available either

detection limits or screening values from other regulatory frameworks (such as United

States Environmental Protection Agency) were used.

Remedial targets were derived for each soil type in each zone with respect to the Riddy

Brook for soil, leachate and groundwater.

4.5 Summary of Previous Works

A CSM and initial remedial targets were developed by Atkins using EA RTW before

remediation commenced for twenty three contaminants of concern. The initial CSM and

derivation of remedial targets was largely based on the existing pre-remediation conditions,

available Enviros and Atkins site investigation data and modelling of the groundwater

regime at the site using MODFLOW.

Subsequently five CoCs (dicamba, schradan, Bis(2-chloroethyl)ether, ethofumesate and

1,2-dichloroethane) were identified as priority CoCs by VertaseFLI and remedial targets for

these were reassessed using ConSim to provide a more detailed probabilistic risk

assessment.


16 Rev A 907BRI

5.0 Conceptual Site Model

5.1 Original CSM

The original CSM for the site was developed by Atkins in 2006 to 2007 and is presented in

Appendix B. The CSM presents a detailed model of the sub-surface contaminant pathways

prior to remediation. The contaminant source is shown as granular Made Ground and

cohesive Made Ground, much of which was located below the water table. The main

environmental receptors were groundwater and surface water (Riddy Brook).

The key groundwater contaminant pathways in the model are:

Vertical migration through the unsaturated zone;

Migration of contaminants through sand and gravel lenses within the cohesive Made

Ground and WMMCF; and

Migration through existing site infrastructure such as sumps and utility trenches.

The original CSM and therefore the initial risk assessment and remedial targets were based

on the available data at the time which comprised the findings of the site investigations and

therefore reflected the pre-remediation site conditions (See sections 4.2 and 4.3) and it was

assumed that the majority of groundwater flow was through the sand and gravel lenses

associated with the WMMCF. Although significant amount of data had been collected, the

investigations were still limited by the presence of buildings and site infrastructure. As

described in Section 3.3.2, additional contaminant sources have been located and treated

during the remediation process that were not identified during the site investigations.

The presence of the bentonite cut off wall and the on-going groundwater abstraction are

also likely to have affected groundwater levels and flow directions on the site and the

presence of site infrastructure such as sumps, and trenches may also have impacted on the

results of pumping tests.

5.2 Post Remediation Site Conditions

5.2.1 Ground Conditions

Post remediation, ground conditions at the site will generally comprise the following three

remediated soil types (see Drawing D907_153, Appendix A):


17 Rev A 907BRI

Type A – Sand and gravels, including granular Made Ground. The total volume is

approximately 10,000 m3 at present;

Type B – Cohesive soils largely comprising the West Melbury Marly Chalk

Formation (WMMCF) including previously reworked material. The total volume is

approximately 62,000 m3 at present; and

Type C – Gault Clay. The total volume is approximately 12,000 m3 at present.

The soil material will be reinstated in layers replicating the distribution of undisturbed soils

prior to development of the site, so that the Type A overlies Type B which will overlie Type

C.

As described in Section 2.1, prior to remediation the distribution of the natural granular

deposits at the site were limited to several shallow discontinuous lenses of sand and gravel.

As a result of this and the limited presence of granular Made Ground there is only a

relatively small volume (10,000 m3 at present) of the Type A material present which is

insufficient to provide cover over the entire site. Given a thickness of 0.3 m the Type A

material would cover approximately 3.5 ha, less than half the area of the site. Therefore, no

Type A material will be placed in Zone 1 and the Type A material is also unlikely to be

continuous over Zones 2S, 2N and 3 replicating the pre remediation distribution of sands

and gravel. The anticipated shortfall in reinstated Type A material in will be made up with

Type B material.

Given the volumes of remediated material and the area of the site, typical thicknesses of

the reinstated units are likely to be as follows:

Type A – Between 0.3 and 0.6 m (where present);

Type B – Between 3 and 5 m; and

Type C – Approximately 0.5 m.

The Type C material (comprising remediated Gault Clay) will be placed directly over a

significant thickness of undisturbed Gault Clay. It should also be noted the development

proposals include the placement of imported low permeability cover material on top of the

reinstated soil material. The cover material will be imported from an off-site source by the

developer following the completion of the remedial works.


18 Rev A 907BRI

5.2.2 Groundwater Flow Through the Site

5.2.2.1 Pre Remediation and Observed Groundwater Conditions

The original CSM for the site assumed groundwater flow at the site was predominantly

through the WMMCF and the associated lenses of sand and gravel. However, as discussed

in Section 3, the lenses of sand and gravel within the WMMCF are relatively small and

discontinuous with the WMMCF typically comprising a stiff clay. Site observations during

the ongoing remediation have indicated that the majority of groundwater flow on site was

through the granular Made Ground, site drainage system and site services result from

periods of rainfall.

The excavations undertaken for the remediation provide a complete cross section through

the top and base of the in-situ WMMCF and there has been negligible flow observed in the

excavation walls other than very slight seepages through the discontinuous lenses of sand

and gravel. The seepages have generally decreased with time following exposure

suggesting very limited recharge from the surrounding marl material as would be expected

from a stiff clay. As a result, the excavations including those below the water table have

also remained dry (with the exception of rainfall) for the duration of the remedial works so

far.

The groundwater contours presented in Appendix B represent the pre-remediation site

conditions. The impact of the dewatering system in the south of the site can be seen with

the presence of a groundwater low and the surrounding groundwater contours indicating

groundwater flow towards the dewatering system. It is likely that the artificial lowering of

groundwater in this area was driving groundwater flow through the sand and gravel lenses

within the WMMCF on site. It is important to note that the sump for the dewatering system

is situated adjacent to a sand and gravel lens so that the volume of groundwater removed is

higher than may be anticipated if it had been installed in the ‘stiff light grey clay’ marl

material.

Therefore, as a result of the groundwater flow induced by the dewatering, the observed flow

in the WMMCF prior to remediation is not considered representative of the post remediation

conditions. Without the dewatering, groundwater levels in the south of the site would return

to natural levels (in the order of 1 m bgl) and the likely groundwater flow rate would be

significantly reduced to rates more comparable with the observed low hydraulic conductivity

and hydraulic gradient in the surrounding natural WMMCF.


19 Rev A 907BRI

5.2.2.2 Comparison of Waste Water Pumping and Rainfall Data

Drainage at the site is designed to collect all surface water, including any groundwater that

may flow into the excavations. Given the existing ground conditions and ground cover it is

anticipated that the majority of rainfall will be collected by the drainage system. Over an 8

month period between September 2010 and April 2011, a total volume of 31,963 m3 was

pumped from the site to the waste water treatment plant (see Appendix C).

Based on the average annual rainfall for the area of 586 mm/year and an approximate site

area of 8.5 ha, over an 8 month period a total rainfall volume of 33,207 m3 would be

anticipated which is very similar to the volume of water pumped from the site. Recorded

rainfall data for Cambridge gave a total rainfall for the same 8 month period of 256.7 mm,

equivalent to 21820 m3 over the site.

A significant proportion of the difference between pumped groundwater volume and total

rainfall volume (approximately 10,000 m3) is likely to result from the very low rainfall in

March and April 2011 (a total of 4.7 mm over both months) and the subsequent use of large

volumes of water on site for dust suppression. During this period, approximately 180 m3 of

water a day was used for dust suppression, equivalent to total of approximately 8,100 m3.

Based on the recorded pumped water volumes relative to local rainfall, and making

allowance for loss of rainfall as evaporation etc there appears to be only a very low

contribution to the pumped water volumes from groundwater ingress into the excavations.

Considering the depth of dewatering achieved (approximately 1 m) this suggests that the

volume of water present in the natural WMMCF including the sand and gravel lenses and

the hydraulic conductivity are generally very low.

5.2.2.3 Reinstated Soil Material and Likely Impact on Local Groundwater Regime

The reinstated Type B and Type C soil material will have been homogenised during the

remediation and compacted. As a result of the sorting and homogenisation of the Type B

material, the discontinuous sand and gravel lenses will no longer be present. Additionally,

all historic site infrastructure and drainage will have been removed and the limited volume

of granular material will be replaced in isolated lenses above the water table. These

activities will have removed the majority of previously identified contaminant pathways and

reduced the hydraulic conductivity/permeability of the reinstated material relative to the

surrounding natural strata.

Without the impact of the current dewatering system in the south of the site and based on

the observed negligible flow through sides of excavations, groundwater flow through the


20 Rev A 907BRI

natural strata surrounding the site and therefore through the reinstated soil material is likely

to be very low. Although the reinstatement of reduced permeability soil material may locally

alter the groundwater regime, given the relatively low hydraulic gradient observed in the

surrounding area, and the lack of significant groundwater flow through the natural WMMCF

and associated sand and gravel lenses, any changes to groundwater levels in and

surrounding the site are not likely to be significant.

5.2.3 Aquifer Parameters

5.2.3.1 Groundwater Levels

Monitoring of groundwater levels before and during remediation indicates that groundwater

levels at the site are shallow, with groundwater typically being encountered between 0.8

and 2 m below ground level.

5.2.3.2 Hydraulic Gradient

The presence of the bentonite cut-off wall and groundwater abstraction on site make

accurately determining the post remediation hydraulic gradient and groundwater flow

direction across the site very difficult. It should also be noted that the MODFLOW models

previously developed by Atkins were based on the original CSM (discussed in Section 5.1)

and site investigation data and reflect the ground conditions at the time including the

presence of granular Made Ground, drainage channels and assumed flow through the

WMMCF. Therefore the modelled groundwater parameters used in previous reports are

unlikely to be fully representative of the remediated site conditions.

Available Atkins groundwater monitoring data from the adjacent wastewater treatment plant

(immediately to the northwest of the site) appears to be outside of the influence of both the

bentonite wall and groundwater abstraction. It is therefore considered most representative

of the local groundwater conditions and the likely post remediation groundwater conditions

on site. The local groundwater flow is in a northeastern direction towards the Riddy Brook

and the local hydraulic gradient is typically between 0.007 and 0.009.

5.2.3.3 Hydraulic Conductivity and Permeability Testing

As the soil material has been largely homogenised as part of the remediation process, the

variability within the reinstated compacted soil material and therefore the variability in

hydraulic conductivity is likely to be significantly reduced relative to ground conditions prior

to remediation. The reinstated soil materials will also be compacted which will further

reduce variability.


21 Rev A 907BRI

In the absence of in-situ soil material that is representative of post remediation conditions,

laboratory permeability testing of the soil material has been undertaken will be broadly

representative of the hydraulic conductivity in the reinstated material.

Results of the laboratory permeability testing are presented in Appendix D.

To date, testing results indicate the permeability of the Type A material to be in the range of

1 x 10-7 to 5 x 10-6 m/s, which is similar to the majority of the hydraulic conductivities

determined by the pumping tests and rising/falling head slug tests undertaken by Atkins.

Testing results in the Type B material indicate permeability of Type B material (in laboratory

conditions) material is in the order of 1 x 10-10 ms-1 with the Type C material likely to have a

permeability in the order of 1 x 10-11 ms-1.

5.3 Post Remediation CSM

The post remediation CSM is presented in Drawing D907_154, Appendix A, based on the

requirement to reinstate soils in their natural sequence (Type A over Type B over Type C).

Due to the relatively small volume of the Type A material (discussed in Section 5.2.1), there

is insufficient material to provide cover over the entire site. Therefore, no Type A material

will be placed in Zone 1 and the Type A material will not be reinstated over all of Zones 2S,

2N and 3. Any shortfall in reinstated material will be made up with Type B material.

Following remediation and reinstatement of the remediated soil material, a 1 m thick clean

cover layer comprising topsoil and low permeability material will be placed on the site. All

material for the cover material will be imported from off-site. The topsoil and low

permeability should have a sufficiently large permeability contrast to maximise run-off and

minimise infiltration of rainwater through the low permeability layer.

5.3.1 Contaminant Source

The contaminant source in the post remediation CSM will comprise the residual

contaminant concentrations remaining in the remediated soils. The source will therefore

extend across the entire site to depths of approximately 5 m below ground level. Soil

material used to create the 20 m buffer zone (Zone 1) will be subject to more stringent soil

assessment criteria which may require the importing of soil material from off-site to ensure

that the reinstated material does not present a significant risk to receptors.

Based on the available volume of each soil type and the typical groundwater depths, it is

anticipated that all Type A material will be reinstated above the current water table with the

majority of the Type B material and all Type C material reinstated below the water table. As


22 Rev A 907BRI

a result of the small volume on site, the Type A material will reinstated so that it is

surrounded by Type B material, isolating the Type A material from contact with the in-situ

natural strata.

5.3.2 Pathways

As a result of the sorting and homogenisation of soil material during remediation, and the

compaction of materials during reinstatement, the pathway through the sand and gravel

lenses in the Type B material will no longer be present. Additionally, the demolition of the

former site buildings and excavation of soil material will have removed the previous

pathways through former site infrastructure such as drainage runs, sumps and trenches.

The following potential pathway is anticipated at the site with respect to controlled waters:

A potential pathway will still exist for vertical migration of contaminants through the

Type B material into groundwater. The groundwater may also act as a pathway to

the nearest surface water course (Riddy Brook). However, given the low

permeability of the reinstated Type B and Type C material, and the negligible

groundwater flow observed in the in-situ WMMCF (discussed in Section 5.2.2.1) any

migration of contaminants is likely to be relatively limited.

It should also be noted that the placement of the low permeability post remediation cover

layer by the developer will further reduce infiltration into the reinstated soil material and

therefore further reduce the potential for leaching of the residual contaminants within the

reinstated soils.

As the Type A will be reinstated as a shallow layer surrounded by low permeability Type B

material and covered with the low permeability cover layer there will be negligible

groundwater flow through the Type A material. No pathway will exist through the Type A

material with the exception of very limited vertical migration through the unsaturated zone,

although given the large permeability contrast between the Type A and Type B materials

any significant migration is unlikely to occur.

5.3.3 Receptor

The primary receptor is considered to be the Riddy Brook, located between 1 and 6 m from

the northeast boundary of the site.


23 Rev A 907BRI

6.0 Selection of Risk Assessment Software and Modelling Approach

6.1 Environment Agency Remedial Targets Methodology

In order to accurately model the risks to the Riddy Brook from the presence of residual

contaminants within the reinstated remediated soils, it is necessary to select a software

model or modelling approach that uses a conceptual model that is applicable to the CSM for

the site. In the UK, most groundwater modelling is conducted in accordance with the

Environment Agency Remedial Targets Methodology (Environment Agency, 2006) (EA

RMT).

6.1.1 Assessment of Risks from Soils

The EA RMT provides the following tiers of risk assessment for contaminated soils:

Level 1: Soil Zone – Considers whether contaminants concentrations in pore water

(leachate) in contaminated soil are sufficiently elevated to represent a risk to the

receptor ignoring all dilution, dispersion and attenuation.

Level 2: Unsaturated Zone and Dilution at the Water Table – Assesses the

attenuation of contaminants in the unsaturated zone and dilution within the aquifer to

determine if these processes are sufficient to reduce the contaminant concentrations

in the aquifer to acceptable levels; and

Level 3: Attenuation in the aquifer – Assesses if attenuation in the aquifer is

sufficient to reduce contaminant concentrations to acceptable levels.

6.1.2 Assessment of Risks from Contaminated Groundwater

The EARTM also provides an assessment framework for situations where elevated

contaminant concentrations recorded in groundwater:

Level 1: Soil Zone – Level 1 is not included in the assessment as the contaminants

are already present in groundwater;

Level 2: Unsaturated Zone and Dilution at the Water Table – Recorded contaminant

concentrations are compared directly with the appropriate groundwater screening

criteria, attenuation in the unsaturated zone and dilution are assumed to have

occurred prior to sampling; and

Level 3: Attenuation in the aquifer - Assessment of attenuation in the aquifer is the

same as the soils assessment.


24 Rev A 907BRI

6.1.3 Conceptual Model

The conceptual model used in the EA RTM assumes the following:

The soil source zone is situated entirely in the unsaturated zone (above the water

table);

All leaching and contaminant movement in the unsaturated zone is vertical; and

Dilution and attenuation of contaminants will occur in the aquifer. All movement of

groundwater is laminar and constant throughout the aquifer.

6.2 Comparison of EA RTM and Site Conceptual Site Model

The principal differences between the conceptual site model described in the EA RTM and

the post remediation CSM (Drawing D907_153) for the site (described in Section 5) are as

follows:

The conceptual model in the EA RTM assumes the contaminant source zone is

located in the unsaturated zone above the water table. However, post remediation

the contaminant source will comprise the residual contamination in the remediated

Type A, B and C material, of which all Type C and much of the Type B material will

be reinstated below the water table; and

The EA RTM assumes vertical migration only in the unsaturated zone. Post

remediation the unsaturated zone will comprise Type A and B material and much

higher permeability in the Type A material is like to result in the majority of any

contaminant migration occurring horizontally in the Type A material.

Given the above, the post remediation CSM is more complex than the conceptual model

detailed in the EA RTM (Level 1 to 3) and a revised approach to modelling the risk to

groundwater and Riddy Brook from the reinstated remediated soil material is therefore

required.

6.3 Risk Assessment Approach

6.3.1 Applicability of EA RTM Risk Assessment Levels

To develop a risk assessment approach and methodology that is appropriate to the site

conditions, consideration to each of the EA RTM levels and therefore the applicability of

groundwater modelling software is needed. Although the overall CSM is more complex

than the EA RTM conceptual model the following assessment levels will still apply to the

site:


25 Rev A 907BRI

Level 1: This level of assessment is still considered to apply to all soil material on

site as it is based on fundamental properties of the soil material (porosity and bulk

density) and contaminants (Henry’s Law constant and soil/water partition coefficient)

only and does not include any allowance for dilution, dispersion or attenuation.

However, it is only intended for use where there is insufficient site specific soil and

leachate analysis to assess the potential leaching of CoCs; and

Level 3 (Groundwater): This level of assessment (Level 3a in ConSim) is suitable to

assess the risks to the Riddy Brook from contaminated groundwater already present

within the Type B and C materials and to derive appropriate remedial groundwater

targets. However, Level 3a of the assessment will not apply to Type A material as

this will be reinstated above the water table.

EA RTM Level 2 and Level 3 assessments will not be appropriate to assess the risks to

groundwater and Riddy Brook as both levels assume the contaminant source is located in

the unsaturated zone whereas the majority of the reinstated soil material (the contaminant

source) will be below the water table with no unsaturated zone. Additionally, for the Type A

material, leachate migration is likely to be predominantly horizontal through the Type A

material towards Riddy Brook without entering the aquifer and the processes modelled in

Level 2 (attenuation and dilution via vertical migration) are therefore not applicable.

6.3.2 Selection of Modelling Software

Level 1 and Level 3 (groundwater) assessments are suitable for use in the assessment of

risks to groundwater and Riddy Brook. Of the available software used undertake Level 1

and Level 3 assessments, it is proposed to use ConSim. ConSim has a number of

advantages over the EA RTW which include the following:

ConSim can take into account multiple contaminant source zones containing

different contaminant concentrations;

ConSim provides a more detailed assessment of attenuation and movement of

contaminants in the aquifer; and

ConSim can undertake probabilistic modelling using Monte-Carlo analysis so that

variations in the model input values can be taken into account to give a 95th

percentile probability of achieving a water quality standard at the receptor.

ConSim is forward modelling software in that it predicts a contaminant concentration at a

receptor based on initial inputs at the contaminant source. Therefore, to determine the CoC


26 Rev A 907BRI

concentrations that do not represent a risk to the receptor (Riddy Brook) it is necessary to

use the software iteratively, continually refining the source CoC concentrations until the

predicted concentration at the receptor does not exceed the selected screening criteria.

6.3.3 Assessing Risks from Type B and C Soil Material

6.3.3.1 Deriving Groundwater/Leachate Target Values

The site CSM is shown in Drawing D907_154, Appendix A. For the type B and C soil

material reinstated below the water table, the Level 3a assessment in ConSim (EARTM

Level 3 groundwater assessment) is suitable to model the movement of contaminants

already present in the aquifer. Using the appropriate screening criteria for the Riddy Brook

as the target threshold, it is therefore possible to use Level 3a to derive target values for

groundwater/leachate within the type B and C material that do not represent a significant

risk to the Riddy Brook.

6.3.3.2 Deriving Soil Target Values

To derive soil target values that are protective of Riddy Brook, the results of laboratory

analysis of soil samples will be directly compared with analysis of leachate from the same

sample. By comparing sufficient data, it should be possible to determine the linear

relationship between contaminant concentrations in soil and leachate and therefore develop

a site specific relationship for each CoC.

Once derived, the linear relationship between soil and leachate contaminant concentrations

will enable concentrations of each CoC in soil to be compared to leachate concentrations.

Therefore, by using the leachate target derived in the Level 3a assessment a soil remedial

target value can also be derived.

Additionally, a Level 1 assessment for each CoC will also be undertaken in ConSim using

site specific input parameters. Using an iterative approach, soil concentrations will be

identified for which the leachate concentration modelled through the Level 1 assessment

does not exceed the groundwater/leachate concentrations derived in Level 3a.

As a conservative measure, the lowest concentration obtained for each CoC from the linear

leachate-soil relationship and Level 1 assessment will be used to provide the soil target

value.

Both approaches for deriving soil target values do not allow for any Level/Tier 2 assessment

and do not allow for any processes in the unsaturated zone or dilution in the aquifer. Both

approaches are therefore appropriate given the presence of the majority of the potential


27 Rev A 907BRI

contaminant source below the water table and will give potentially conservative values as it

is assumed that there is no dilution of leachate concentrations within the aquifer

It should also be noted, that this method of deriving soil target values will also be suitable to

provide a conservative assessment of the Type B material that is reinstated above the

water table.

6.3.3.3 Site Zoning

As in the previous risk assessment model developed by Vertase, for the purposes of the

risk assessment, the site will be split into four zones (shown in drawing D907_134,

Appendix A) as follows:

Zone 1 - Zone 1 represents a 20m buffer zone between the site boundary adjacent

to Riddy Brook and the rest of the site. The site boundary is typically between 1 and

6 m from the Riddy Brook. This buffer zone would have lower remedial targets in

order to offer a degree of protection and allow more achievable remedial targets in

the rest of the site;

Zone 2N and 2S - Zone 2 covers the area between 20 m and approximately 150 m

from Riddy Brook. To give further flexibility in the risk assessment and due to the

large area covered Zone 2 has been divided into Zone 2S and Zone 2N. The

boundary between 2S and 2N was selected so that 2N is largely outside the

influence of Zone 3 and therefore any cumulative effects of contaminants within this

area; and

Zone 3 - Zone 3 is located to the southwest of the site at distance greater than 150

m from Riddy Brook.

6.3.4 Assessing Risks from Type A Soil Material

Due to the small volumes of Type A material on site (approximately 10,000 m3) there is not

sufficient Type A material to be reinstated over the entire site. As shown in the CSM

(drawing D907_154, Appendix A), no Type A material will be present in Zone 1 and it will

not be continuous over the whole of Zones 2S, 2N and 3. Where Type A material is absent,

it is proposed that it is replaced in Zone 1 by Type B material.

To provide an assessment of the potential risks from any migration of residual CoC from the

Type A material the following assumptions will be made about its properties and

distribution:


28 Rev A 907BRI

The Type A material is uniform across the site (where present) will extend to the

boundary with Zone 1. In reality, the Type A material is likely to be reinstated further

away from the Riddy Brook (as shown in Drawing D907_154);

All leachate generated within the Type A material will migrate horizontally towards

the Riddy Brook through the Type A material to within 2 m of the boundary with

Zone 1;

There will be no attenuation or biodegradation of leachate concentrations within the

Type A material;

Leachate from the Type A material will directly enter the groundwater within the

Type B material with no attenuation in the unsaturated zone or dilution in the aquifer;

and

The Type A material will also be assumed to be a non declining source.

Therefore, the risks from the Type A Soil Material will be modelled using two zones as

shown in drawing D907_169:

Zone 1 – The 20m buffer zone between Riddy Brook and the rest of the site; and

Zone 2a – A thin strip running the length of the boundary with Zone 1, representing the

area where all Type A leachate will flow to before entering groundwater.

To provide targets for the Type A material, the same approach will be taken as the Type B

and C, with the aquifer flow (through the 20m buffer zone) modelled using the ConSim

Level 3a analysis, and assessment of soil-leachate relationships and/or Level 1 assessment

to provide a conservative comparison of soil concentrations and leachate/groundwater

concentrations.


29 Rev A 907BRI

7.0 Model Inputs

7.1 Contaminant Sources

Each of the different zones in the model is set as a contaminant source.

Leachate/groundwater concentrations are specified for each CoC for each source. Table 5

below lists the CoC identified by Atkins for further risk assessment.

Table 5: Contaminants of Concern

Contaminant Contaminant Type

Dicamba Pesticide/Herbicide

MCPA Pesticide/Herbicide

Mecoprop Pesticide/Herbicide

Bis(2-chloroethyl)ether Chlorinated Hydrocarbon (Breakdown product)

Schradan Pesticide/Herbicide

Dichloroprop Pesticide/Herbicide

4,6-Dinitro-o-cresol Pesticide/Herbicide

1,2-Dichloroethane Chlorinated Hydrocarbon (Breakdown product)

Ethofumesate Pesticide/Herbicide

Cyclohexanone Aromatic Hydrocarbon (Solvent)

Hempa Pesticide/Herbicide

Vinyl chloride Chlorinated Hydrocarbon (Breakdown Product)

Phenol Aromatic Hydrocarbon (Breakdown Product)

Trichloroethene Chlorinated Hydrocarbon (Breakdown Product)

Tetrachloroethene Chlorinated Hydrocarbon (Breakdown Product)

1,2-Dichorobenzene Chlorinated Aromatic Hydrocarbon (Breakdown Product)

Toluene Aromatic Hydrocarbon (Process Chemical – BTEX)

Simazine Pesticide/Herbicide

Dimefox Pesticide/Herbicide

2,4,6-Trichlorophenol Chlorinated Aromatic Hydrocarbon (Breakdown Product)

Xylene Aromatic Hydrocarbon (Process Chemical –


30 Rev A 907BRI

BTEX)

4-chloro-2-methylphenol Chlorinated Aromatic Hydrocarbon (Process Chemical and Breakdown Product)

Cis-1,2-Dichloroethene Chlorinated Hydrocarbon (Breakdown Product)

7.2 Receptors

Two receptor points were selected along the Riddy Brook. “Riddy Brook 1” is situated at

the Riddy Brook down hydraulic-gradient (based on the presumed groundwater flow

direction to the northeast) of the widest part of zone 2N. “Riddy Brook 1” therefore receives

groundwater moving through Zone 2N and Zone1 at their widest point. “Riddy Brook 2” is

the second receptor point and is situated down groundwater gradient of the southern part of

the site, again down hydraulic-gradient of the widest part of the site including Zone 3, Zone

2S and Zone 1 and is potentially most sensitive to the cumulative effects of the three zones.

7.3 Selection of Screening Criteria

To assess the risks to the Riddy Brook, Environmental Quality Standards (EQS) values are

used where available. Where EQS values are not available UK Drinking Water Standards

(DWS) are used, and where neither is available detection limit is used, unless a value from

another regulatory framework is considered appropriate. The selected water quality

standards are presented in Table 6.

Table 6 - CoC Selected Water Quality Standards

Contaminant Screening Criteria

(ug/l) Source Justification

1,2-Dichloroethane

10 EQS Freshwater

Dicamba 10 Canadian EQS for

Fresh Water

Water quality guidelines for the protection of aquatic life more appropriate for protecting

Riddy Brook than UK DWS

Schradan 0.1 UK DWS Limit for pesticides other than Aldrin,

Dieldrin, Heptachlor and Heptachlor epoxide

Bis(2-chloroethyl)ether

1 Limit of Detection No other screening value available

Ethofumesate 0.1 UK DWS Limit for other Pesticides

Trichloroethene 10 UK DWS Limit for other Pesticides

Tetrachloroethene 10 UK DWS Limit for other Pesticides


31 Rev A 907BRI

Contaminant Screening Criteria

(ug/l) Source Justification

Cis 1,2, Dichloroethene

0.1 Limit of Detection

Vinyl Chloride 0.5 UK DWS

Cyclohexanone 1 Limit of Detection No other screening value available

Hempa 0.1 UK DWS Limit for other Pesticides

1,2 Dichlorobenzene

1 Canadian

Freshwater EQS

2,4,6 Trichlorophenol


4,6 Dinitro-o-cresol

0.1 UK DWS Limit for other Pesticides

4-Chloro-2 methylphenol


Dichlorprop 0.1 UK DWS Limit for other Pesticides

Dimefox 0.1 UK DWS Limit for other Pesticides

MCPA 0.1 UK DWS Limit for other Pesticides

Mecoprop 0.1 UK DWS Limit for other Pesticides

Phenol 0.5 UK DWS

Simazine 0.1 UK DWS Limit for other Pesticides

Toluene 50 EQS Freshwater

Xylenes 30 EQS Freshwater

7.4 Selection of Aquifer Pathway Parameters – Level 3a Assessment

As discussed above, the Level 3a assessment is only relevant for modelling the migration of

contaminants through the Type B and Type C soil material as all Type A material will be

situated above the water table. For the Level 3a assessment, the following hydrogeological

parameters are required:

Aquifer Thickness;

Dry Bulk Density;

Mixing Zone Thickness;

Hydraulic Conductivity;

Effective Porosity;

Hydraulic Gradient;


32 Rev A 907BRI

Groundwater Flow direction;

Longitudinal and Lateral Dispersivity; and

Fraction of Organic Carbon.

For the purposes of modelling, the reinstated Type B and Type C materials are considered

to form a single aquifer. As most of the aquifer will be formed by the Type B material and

this is more permeable, the risk assessment will be conservatively conducted using the

parameters for the Type B soil material.

7.4.1 Aquifer Thickness

The assumed reinstated aquifer thickness is conservatively based on the original site

investigation data and the volume of Type B material excavated. A triangular probability

distribution function (PDF) has been used within ConSim with minimum and maximum

aquifer thicknesses of 3 and 5 m respectively and typical thickness of 4 m.

7.4.2 Dry Bulk Density

The dry bulk density of the Type B material is based on geotechnical laboratory data

presented in Appendix D. For the Type B material, the dry bulk density ranged from 1.51 to

1.7 gcm-3 with an average value of 1.63 gcm-3. Based on the available data a triangular

distribution was selected.

7.4.3 Mixing Zone Thickness

The mixing zone thickness is calculated by ConSim.

7.4.4 Hydraulic Conductivity

Permeability testing has been undertaken on compacted samples taken from the site.

Given the homogenisation of the soil material that has taken place as part of the remedial

works and the likely compaction of soil material when it is reinstated it is considered that the

permeability values obtained will be representative of the reinstated soil material.

For the Type B material, geotechnical testing has given a range of permeabilities in the

order of 1 x 10-10 ms-1 and the Type C material permeability was in the order of 1 x 10-11

ms-1. Given the testing was undertaken under laboratory conditions and may not be

completely representative of the post remediation site conditions, a range of hydraulic

conductivities of 1 x 10-9 to 1 x 10-7 m/s with a loguniform PDF has been selected. The

loguniform PDF was chosen due to the variation of 2 order of magnitude in the selected

inputs.


33 Rev A 907BRI

7.4.5 Effective Porosity

As part of the remediation, reinstated soil material will be significantly compacted as it is

placed. Effective porosity can be estimated from geotechnical compaction tests. At the time

of writing compaction tests had been undertaken on Type B material which indicated a

minimum air voids percentage (taken as equal to the effective porosity) of approximately

3%. The compaction testing indicated that for the upper levels of compaction achievable in

the Type B soil material, an air voids percentage of 3 to 7 % would be representative.

Therefore, a uniform PDF between 3 and 7 % effective porosity has been assumed for the

soil material in the model.

7.4.6 Hydraulic Gradient

As discussed in Section 5.2.2, current groundwater conditions are significantly affected by

the presence of the bentonite wall along the Riddy Brook and the continued groundwater

abstraction both of which will be removed as part of the remediation of the site.

Consequently, all groundwater data obtained from the site to date and therefore the

hydraulic gradient values obtained from the MODFLOW model based on this data are not

considered representative of the likely post remediation groundwater regime.

For the purposes of developing the ConSim model, groundwater data obtained as part of

the Atkins 2006 investigation in the waste water treatment plant (WWTP) has been used to

provide an assessment of the likely hydraulic gradient. The WWTP is located immediately

to the northwest of the site and the groundwater contours (see Appendix B) indicate that it

is outside the zone of influence of both the bentonite cut-off wall and the groundwater

abstraction. Given the proximity to the site and similar topography it is therefore considered

that groundwater data from this area will be indicative of the likely hydraulic gradient at the

site on completion of remediation.

The groundwater contours in Appendix B give a hydraulic gradient between 0.007 and

0.009 across the WWTP. However, to reflect the lack of site specific data a conservative

range of hydraulic gradients of 0.01 to 0.03 with a uniform PDF has been included in the

model.

7.4.7 Groundwater Flow Direction

Post remediation, and following the removal of the bentonite wall and cessation of the

groundwater abstraction, groundwater flow on the site is anticipated to be in a northeastern

direction towards Riddy Brook. This is confirmed by groundwater monitoring data from the

WWTP which shows groundwater flow direction to the northeast (see Appendix B).


34 Rev A 907BRI

7.4.8 Dispersivity

Based on the guidance given in both the EARTM and ConSim help files longitudinal

dispersivity is assumed to be 10% of the contaminant pathway, with the lateral dispersivity

assumed to be 30% of the longitudinal dispersivity.

Based on the most conservative pathway length, the distance from the buffer zone to Riddy

Brook (1 to 6 m), uniform PDF has been used for both longitudinal and lateral dispersivity

with values in the range 0.1 to 0.6 m and 0.033 to 0.2 m respectively.

7.4.9 Fraction of Organic Carbon

At the time of writing, values for FOC had been obtained for 33 soil samples taken from the

remediated Type B material which are presented in Appendix E together with histograms

showing the distribution. Based on the histograms, a logtriangular distribution was selected

with minimum and maximum values of 0.75 and 4.8 respectively and a mean value of 1.78.

It should be noted that the FOC values are for the remediated soil materials which include

organic material added as part of the remedial process. Given the available validation data,

residual levels of CoCs in any of the treatment beds are generally limited to a few CoCs and

it is considered that FOC is therefore sufficient to be available to all remaining residual

CoCs in the reinstated soil material.

7.4.10 Summary

Table 7: Summary of ConSim Aquifer Inputs

Aquifer Property (unit)

PDF (Property value) Source

Aquifer thickness (m) Triangular (3.0, 4.0, 5.0) Site specific data from previous site investigations

Dry bulk density (g/cm3)

Triangular (1.51,1.63,1.7) Site specific geotechnical data

Mixing Zone thickness (m)

NA Calculated by ConSim

Hydraulic conductivity (m/s)

Log Uniform (1e-9, 1e-7)

Conservative values given laboratory calculated values in the order of 1 x 10-10 m/s for Type B material

Effective Porosity (%) Uniform (3,7) Conservative assumption based on low permeability material

Hydraulic gradient Uniform (0.01,0.03) Conservative

Groundwater flow Single (45o) Site specific groundwater observations and off site


35 Rev A 907BRI



direction (degrees) groundwater monitoring data

Longitudinal Dispersivity (m)

Uniform (0.1,0.6) 10% of distance from Zone 1 to Riddy Brook

Lateral Dispersivity (m) Uniform (0.033,0.2) 30% of Longitudinal Dispersivity

Fraction of organic carbon (%)

Logtriangular (0.75,1.78,4.8)

Site specific data for Type B soil material

7.4.11 Model Settings

The model have been run with 1001 iterations and the following time slices: 1; 2; 5; 10; 25;

50; 100; 250; 500; 1,000; and 10,000 years.

7.4.12 Model Correlations

Several aquifer parameters are directly related to other aquifer parameters. ConSim allows

these relationships to be included in the model by enabling the user to set correlations

between parameters. Correlations can be set between -1 to +1 where +1 is a total

correlation, -1 is an inverse correlation and 0 is equal to no correlation. For the purposes of

the model, the following correlations have been set:

Longitudinal and Lateral dispersivity are both functions of the length of the

contaminant pathway with Longitudinal dispersivity set at 10% of the contaminant

pathway and lateral dispersivity 30% of the longitudinal dispersivity. Therefore a

correlation of 1 between the two values has been selected;

Hydraulic gradient and hydraulic conductivity are inversely proportional. However,

to allow for some natural variation in aquifer properties a correlation of -0.5 was

selected; and

Effective porosity is generally proportional to hydraulic conductivity. Therefore, to

model this relationship, but allow for natural variations in the aquifer properties a

correlation between the two parameters of 0.5 was selected.

7.5 Soil Source Parameters – Level 1 Assessment

The ConSim Level 1 assessment requires the following soil parameters

Dry Bulk Density;


36 Rev A 907BRI

Fraction of Organic Carbon (FOC); and

Total soil Porosity – Calculated from soil moisture content, dry density and particle

density.

With the exception of the dry bulk density for the Type A soil material, values for all

parameters have been obtained from laboratory analysis (geotechnical and chemical) of the

different soil types although it should be noted that the FOC for the Type A material is

based on the range of values in the Atkins and Enviros reports and additional organic

matter has since been added to the soil material as part of the remediation process. The

model will be revised with site specific values for the dry bulk density and FOC of the

remediated Type A material when this data is available.

Where sufficient data has been obtained, appropriate PDFs have been selected based on

the histogram of the data. The inputs are summarised in Table 8

Table 8: Summary of ConSim Soil Source Inputs



Type A Soil Material

Particle Density (g/cm3) Single (2.78) Standard value taken from EA RTW


Uniform (1.37,1.81) ConSim suggested range for gravelly sand

Moisture Content (%) Normal (10.33,2.95) Based on distribution of site specific data.

Fraction of Organic Carbon (%)

Loguniform (0.72,5.8) Site specific values taken from Atkins and Enviros reports

Type B and C Soil Material

Particle Density (g/cm3) Uniform (2.69,2.73) Site specific geotechnical data


Triangular (1.51,1.63,1.7) Site specific geotechnical data

Moisture Content (%) Triangular (8.5,16,22) Based on distribution of site specific data.

Fraction of Organic Carbon (%)

Logtriangular (0.75,1.78,4.8)

Site specific data for Type B soil material


37 Rev A 907BRI

7.6 Contaminant Parameters

For the purposes of the risk assessment four physio-chemical properties were required for

each CoC:

Soil Organic Carbon to Water Partition Coefficient - Koc (ml/g);

Henry’s Law Constant (Dimensionless);

Biodegradation half life in groundwater (days or years); and

Maximum solubility in water (mg/l).

Since the risk assessments were first undertaken by Atkins in 2006 to 2007, a number of

new sources of physio chemical properties have been released including the Environment

Agency document ‘Compilation of Data for Priority Organic Pollutants for Derivation of Soil

Guideline Values, Scientific Report, SC050021/SR7’. As a result of the availability of this

and other new sources of data, all the four physio-chemical properties were reassessed for

each CoC. The revised CoC parameters are presented in Appendix F together with

justification for the selection of appropriate PDFs. The literature values for the four physio-

chemical parameters for each CoC together with histograms of Koc and Henry’s Law

Constant (where sufficient data was available) are presented in Appendix G. The chemical

parameters are summarised in Table 9 below.

Table 9 - Contaminant Physio-chemical Properties

Contaminant Parameter Unit PDF Min Most Likely

Max S/D

1,2-Dichloroethane

Koc ml/g Uniform 11.48 ~ 76 ~

Henry’s Law constant Normal 0.049 ~ ~ 0.025

Aquifer Half Life days Uniform 400 ~ 720 ~

Maximum Solubility mg/l Uniform 8520 ~ 8680 ~

Dicamba Koc ml/g Log triangular 0.1 2.5 42.65 ~

Henry’s Law constant Uniform 8.87e-9 ~ 8.91e-8 ~


Maximum Solubility mg/l Single 8310 ~ ~ ~

Schradan Koc ml/g Loguniform 0.31 ~ 7 ~

Henry’s Law constant Loguniform 2.58e-15 ~ 1.55e-8 ~


38 Rev A 907BRI


Max S/D


Maximum Solubility mg/l Single 1e6 ~ ~ ~


Koc ml/g Uniform 13.8 ~ 76 ~




Ethofumesate Koc ml/g Uniform 97 ~ 245 ~




Trichloroethene Koc ml/g Logtriangular 25.12 141 776.24 ~

Henry’s Law constant Uniform 0.275 ~ 0.55 ~



Tetrachloroethene Koc ml/g Triangular 50 296 500 ~

Henry’s Law constant Triangular 0.1 0.68 1.21 ~


Maximum Solubility mg/l Triangular 200 225 230 ~


Koc ml/g Uniform 35.6 ~ 69.18 ~

Henry’s Law constant LogTriangular 0.129 0.185 0.303 ~



Vinyl Chloride Koc ml/g Triangular 2.99 16.6 57 ~




Cyclohexanone Koc ml/g Uniform 10 ~ 66.53 ~




Hempa Koc ml/g Single 34 ~ ~ ~

Henry’s Law constant Single 8.17e-7 ~ ~ ~



39 Rev A 907BRI


Max S/D


1,2 Dichlorobenzene

Koc ml/g Triangular 109 379 891 ~

Henry’s Law constant LogTriangular 0.049 0.0786 0.151 ~




Koc ml/g Logtriangular 109 1513 6918 ~

Henry’s Law constant Triangular 5.32e-5 1.176e-4 3.18e-4 ~




Koc ml/g Triangular 100 257 602 ~





Koc ml/g Uniform 124 ~ 700 ~




Dichlorprop Koc ml/g Uniform 34 ~ 170 ~

Henry’s Law constant Loguniform 1.09e-7 3.6e-4 ~



Dimefox Koc ml/g Single 2.2 ~ ~ ~




MCPA Koc ml/g Uniform 10 ~ 154 ~




Mecoprop Koc ml/g Uniform 5.3 ~ 68 ~




40 Rev A 907BRI


Max S/D


Phenol Koc ml/g Uniform 10 ~ 46.77 ~




Simazine Koc ml/g Triangular 39.81 140 421.7 ~



Maximum Solubility mg/l Uniform 3.5 ~ 7.4 ~

Toluene Koc ml/g Triangular 38.9 160 269.15 ~




Xylenes Koc ml/g Triangular 74 250 616.59 ~





41 Rev A 907BRI

7.6.1 Selection of Parameters

The range of literature values was assessed to find the best fit range of values and PDF.

For a number of the CoCs, several literature values were significantly higher or lower than

the typical range of values. In these cases, values that were not considered representative

or those which did not fit the most appropriate PDF were discounted.

7.6.1.1 Aquifer Half Lives

The only available source of half life data for the CoCs was Physical – Chemical Properties

and Environmental Fate for Organic Chemicals, 2nd Edition, Mackay et al, 2006 where half

lives were typically reported as a range based upon a maximum and minimum half life.

Conservatively, anaerobic biodegradation half lives in water were used in the model.

Where more than one range of values were available, the two most conservative values in

any of the ranges was used as the input

For a number of CoCs, no literature values for half life in water were available. In these

cases a conservative anaerobic half life range of 5 to 10 years was assumed, which was

more conservative than the range 100 to 730 days used in previous models (see Section

4.3.2.2)

7.6.1.2 Calculating Kd

The values for Koc are multiplied by the fraction of organic carbon to derive Kd, the soil-water

patrician coefficient. In previous risk assessments for the site, Kd was calculated based

upon average values of the Fraction of Organic Carbon (FOC) for soil material, above and

below the water table. As detailed in Section 3.3.2.2, as an extra factor of safety was

incorporated into the Atkins model by only using 10% of the calculated Kd value.

ConSim can either use inputs for Kd or calculate Kd from the Koc and FOC. As ConSim is

designed to model a range of inputs using PDFs it was considered more appropriate to use

the available range of Koc and FOC data and suitable PDF to provide the most realistic

model. Given that the output model reflects the 95th percentile worst case values it was not

considered necessary to add any additional factor of safety to the model at this stage.


42 Rev A 907BRI

8.0 Model Outputs

8.1 Leachate/Groundwater Maximum CoC Threshold Values

Based upon the model inputs and screening criteria discussed in Section 7, the following

models have been run to derive leachate/groundwater maximum CoC threshold values:

ConSim Level 3a assessment for Type A material as detailed in Section 6.4.3; and

ConSim Level 3a assessment for Type B and C material as detailed in Section

6.4.2.

Due to the number of CoCs each model was split into two parts:

Part 1 – 1,2 Dichloroethane, Dicamba, Schradan, Bis(2-chloroethyl)ether,

Ethofumesate, Trichloroethane, Tetrachloroethane, Cis 1,2 dichloroethane, Vinyl

Chloride, Cylohexanone and Hempa; and

Part 2 – 1,2 Dichlrobenzene, 2,4,6 Trichlorophenol, 4,6 Dinitro-o-cresol, 4 Chloro 2

methylphenol, Dichlorprop, Dimefox, MCPA, Mecoprop, Phenol, Simazine, Toluene

and Xylene.

The threshold values represent the maximum concentration of each CoC that will not

represent a significant risk to the Riddy Brook, the closest controlled water receptor. The

model inputs and outputs are presented in Appendixes H and I. The derived

leachate/groundwater maximum thresholds for the Type A and Type B and C soil material

are summarised in Table 10 below. It should be noted that as in the post remediation CSM,

no Type A material will be placed in Zone 1.

Table 10 - Leachate/Groundwater Maximum CoC Threshold Values Zones - Type A Material (µg/l)

Zones - Type B & C Material (µg/l) Contaminant

2 1 2S 2N 3

1,2-Dichloroethane

8,000,000 1,000 8,000,000 8,000,000

8,000,000

Dicamba 5,000 50 5,000 10,000 20,000

Schradan 5 0.1 200 2,000 5,000


1,000,000 50 1,000,000 1,000,000

5,000,000

Ethofumesate 20,000 50 20,000 50,000 50,000


43 Rev A 907BRI

Zones - Type A Material (µg/l)

Zones - Type B & C Material (µg/l) Contaminant

2 1 2S 2N 3

Trichloroethene 1,200,000 1,000 1,200,000 1,200,000 1,200,000

Tetrachloroethene 230,000 1,000 230,000 230,000 230,000


4,900,000 1,000 4,900,000 4,900,000

4,900,000

Vinyl Chloride 10,000 10 1,000,000 2,700,000 2,700,000

Cyclohexanone 25,000 50 1,000,000 5,000,000 10,000,000

Hempa 15,000 1 700,000 5,000,000 10,000,000

1,2 Dichlorobenzene

100,000 1,000 100,000 100,000

150,000


50,000 1,000 50,000 50,000

500,000


200,000 1,000 200,000 200,000

250,000


100,000 1,000 100,000 100,000

1,000,000

Dichlorprop 10 0.1 5,000 10,000 20,000

Dimefox 5 0.1 200 1,000 2,000

MCPA 500,000 1,000 500,000 500,000 600,000

Mecoprop 620,000 1,000 620,000 620,000 500,000

Phenol 100,000 1,000 100,000 200,000 1,000,000

Simazine 7,400 1,000 7,400 7,400 7,400

Toluene 100,000 1,000 100,000 200,000 500,000

Xylenes 100,000 1,000 100,000 200,000 200,000

8.2 Soil Maximum CoC Threshold Values

8.2.1 Comparison of Leachate and Soil CoC concentrations

CoCs were analysed for both soil and leachate from the same soil sample and the results

plotted on a graph for each CoC. This was repeated for several samples for each soil

material type and the graph was then used to determine the linear relationship between soil

and leachate concentrations for each CoC.

As a result of the CoC concentrations being below detection limits in a large number of the

soil samples analysed, at the time of writing sufficient data was only available to assess

Ethofumesate and Schradan in the Type B soil material. As more data is obtained, where


44 Rev A 907BRI

the data allows, all CoCs will be assessed and the graphs for Ethofumesate and Schradan

reassessed.

The graphs for Ethofumesate and Schradan are presented in Appendix J.

8.2.1.1 Ethofumesate

Based on the graph for Ethofumesate, there is a clear linear relationship between the

concentration in soil and the resulting concentrations in the Type B soil material.

Discounting some of the highest soil concentrations from the best fit (so the relationship

becomes more conservative) gives a soil:leachate gradient of 0.0884. Therefore, based on

the ConSim Level 3a leachate targets presented in Section 8.1, the soil CoC maximum

threshold value for Ethofumesate are:

Zone 1: 565 ug/kg;

Zone 2 Type A: 226,244 ug/kg;

Zone 2S Type B & C: 226,244 ug/kg; and

Zone 2N and Zone 3 Type B & C: 565,610 ug/kg

8.2.1.2 Schradan

The graph for of the soil leachate relationship for Schradan shows no clear relationship

between concentrations in soil and leachate. This relationship will be reassessed as further

data becomes available.

8.2.2 ConSim Level 1 Assessment

As discussed in Section 6.3, in addition to the direct comparison of soil and leachate CoC

concentrations, a ConSim Level 1 risk assessment has also been carried out to provide

further assessment of maximum CoC threshold values that will not represent a risk to the

Riddy Brook. The model inputs of the Type A and Type B & C material are presented in

Appendixes H and I respectively and the models presented in Appendix K. The derived

threshold values are presented in Table 11 below.


45 Rev A 907BRI

Table 11 - Soil Maximum CoC Threshold Values with Respect to Controlled Waters

Zones - Type A Material (µg/kg)

Zones - Type B & C Material (µg/kg) Contaminant

2 1 2S 2N 3

1,2-Dichloroethane

1,500,000 300 2,000,000 2,000,000 2,000,000

Dicamba 250 5 500 1,000 2,500

Schradan 0.3 0.01 20 200 500


200,000 20 200,000 400,000 2,000,000

Ethofumesate 20,000 80 20,000 50,000 50,000

Trichloroethene 550,000 700 650,000 650,000 650,000

Tetrachloroethene 225,000 800 270,000 270,000 270,000


1,900,000 80 2,500,000 2,500,000 2,500,000

Vinyl Chloride 2,000 2 400,000 800,000 800,000

Cyclohexanone 5,000 1 200,000 1,000,000 2,000,000

Hempa 3,000 0.3 300,000 2,000,000 4,500,000

1,2 Dichlorobenzene

100,000 2,000 100,000 100,000 150,000


50,000 2,000 50,000 50,000 500,000


175,000 1,000 200,000 200,000 250,000


100,000 2,000 100,000 100,000 1,000,000

Dichlorprop 5 0.05 1,000 2,000 5,000

Dimefox 0.3 0.01 20 50 200

MCPA 125,000 400 200,000 200,000 225,000

Mecoprop 70,000 100 100,000 100,000 100,000

Phenol 20,000 100 20,000 50,000 200,000

Simazine 2,250 1,000 3,500 3,500 3,500

Toluene 100,000 1,000 100,000 200,000 400,000

Xylene 100,000 2,000 100,000 200,000 200,000

8.2.3 Comparison of Soil Threshold Values

Presently, remedial targets based on the soil-leachate CoC concentration relationship have

been derived for Ethofumesate only. These values are typically an order of magnitude

greater than those derived using the ConSim Level 1 risk assessment. Therefore, the


46 Rev A 907BRI

threshold values derived for Ethofumesate using ConSim are conservatively recommended

to assess the risks to the Riddy Brook.

Further comparison and selection of the threshold values will be undertaken as the

relationship between leachate and soil CoCs are determined.


47 Rev A 907BRI

9.0 Summary

The previous risk assessments undertaken by both Atkins and VertaseFLI at the site were

based on a conceptual model developed before remediation commenced at the site. The

remediation, which at the time of writing was still continuing, has allowed the collection of

large amounts of data leading to an improved understanding of the post remedial ground

conditions so that a revised conceptual site model (CSM) could be developed which

accurately reflects the likely conditions once remediation is complete.

As a result of the revisions to the CSM, the risk assessment approach has also been

revised so that it is appropriate to fully assess the risks to controlled waters (i.e. the Riddy

Brook) from the remediated site. The revised methodology used ConSim to derive

maximum COC threshold values for leachate and groundwater at the site. ConSim was also

used to assess the relationship between soil and leachate CoC concentrations together with

site specific relationships based on lab testing results.

To derive maximum CoC threshold values using ConSim, the contaminant inputs for all 23

CoCs have been reassessed based on a review of available literature values and if

necessary revised. Aquifer parameters were revised based on site specific data. Using

these reassessed values and the revised risk assessment approach has enabled a model

more representative of the post remediation site conditions to be developed and therefore

more representative maximum CoC threshold values to be derived.

9.1 Further Work

The threshold values listed in Table 11 represent the maximum CoC concentrations in the

reinstated soils that will not represent a significant risk to the Riddy Brook. However, it is

intended that the soil material will be remediated to a much higher standard and therefore

where possible, much more stringent remedial targets will be used. The remedial targets

will be detailed in a subsequent report and will take into account the human health risk

assessment (being revised by Atkins at the time of writing) to ensure that the remediated

ground conditions do not represent a risk to any of the identified receptors.

As the remediation of the site continues, further data will be collected as part of the

remediation and validation process. All additional data will continue to be incorporated into

the risk assessment model, increasing the certainty of the modelled site geometry and

hydrogeological parameters and further increasing the accuracy of the model. This in turn


48 Rev A 907BRI

will allow the continued development and of the maximum CoC threshold values and

therefore the remedial targets, and will ultimately provide a satisfactory demonstration that

the remediated site does not represent a risk to controlled waters.


Rev A 907BRI

APPENDIX A

VERTASE FLI DRAWINGS


Rev A 907BRI

APPENDIX B

ATKINS DRAWINGS

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Rev A 907BRI

APPENDIX C

WATER PUMPING VOLUMES

Site Pumping and Rainfall Data Comparison

Month Rainfall(mm) Site Rainfall Volume (m3) Volume Pumped (m3)

Sep 55.1 4683.5 4654

Oct 55.2 4692 4264

Nov 26 2210 3829

Dec 22.7 1929.5 3028

Jan 61.6 5236 5769

Feb 31.4 2669 3592

Mar 3 255 4052

Apr 1.7 144.5 2775

Total 256.7 21819.5 31963

Monthly pumped volumes from site pumping data

Rainfall volume calculated based on an approximate site area of 8.5 ha

Local Rainfall data taken from Cambridge Universtiy botanic gardens ‐

http://www.botanic.cam.ac.uk/Botanic/Page.aspx?p=27&ix=2830&pid=0&prcid=0&ppid=0

Average rainfall for the site (from MORECS data) ‐ 586 mm/year

For a 8 month period (Sep to Apr) this would give a site rainfall volume of 33206.67 m3


Rev A 907BRI

APPENDIX D

GEOTECHNICAL RESULTS

BS1377 : Part 5 : Clause 5 :1990

Determination of Permeability by the Constant Head Method

Description:Sample Id: TB 124 Brown silty slightly clayey SAND with much fine to medium gravel

SPECIMEN DETAILS

Depth within original sample n/a

Orientation within original n/a

Specimen preparation Firmly hand tamped in 4 layers.

TEST DETAILS

INITIAL

Diameter mm 77.0

Height mm 174.0

Moisture Content % 8.9

Bulk Density Mg/m³ 2.04

Dry Density Mg/m³ 1.88

Permeability, k m/s 4.1 x 10-6

Checked and Project Number:

Approved GEO / 16602

Initials: Project Name: GEOLABSCFW 907BRI

Date: 01/03/11

Test Report by GEOLABS Limited Bucknalls Lane, Garston, Watford, Hertfordshire, WD25 9XX © GEOLABS LIMITED (Ref4603.617130) Page 1 of 1

Authorised Signatories: [] J R Masters (Qual Mgr) [x] C F Wallace (Tech Mgr) • J M M Powell (Tech Dir)

Client: Vertase FLI Limited, Number One, Middle Bridge Business Park, Bristol Road, Portishead BS20 6PN GEOLABS®GEOLABS LIMITED ®

0 1 2 3 4 50

2

4

6

Hydraulic Gradient

Flo

w R

ate

(m

L/m

in)

Measured Values Laminar Flow Best Fit

®

BS1377 : Part 5 : Clause 5 :1990

Determination of Permeability by the Constant Head Method

Description:Sample Id: TB 127 Brown silty clayey SAND with much fine to medium gravel

SPECIMEN DETAILS

Depth within original sample n/a

Orientation within original n/a

Specimen preparation Firmly hand tamped in 4 layers.

TEST DETAILS

INITIAL

Diameter mm 77.0

Height mm 180.9

Moisture Content % 8.7

Bulk Density Mg/m³ 1.93

Dry Density Mg/m³ 1.77

Permeability, k m/s 3.3 x 10-7



Initials: Project Name: GEOLABSCFW 907BRI

Date: 01/03/11


Authorised Signatories: [] J R Masters (Qual Mgr) [x] C F Wallace (Tech Mgr) • J M M Powell (Tech Dir)

Client: Vertase FLI Limited, Number One, Middle Bridge Business Park, Bristol Road, Portishead BS20 6PN GEOLABS®GEOLABS LIMITED ®

0 2 4 6 80

0.2

0.4

0.6

0.8

Hydraulic Gradient

Flo

w R

ate

(m

L/m

in)

Measured Values Laminar Flow Best Fit

®

BS1377 : Part 2 : Clause 9 : 1990

Determination of Particle Size Distribution

Borehole Number: TB21 Description:Sample Number: - Brown silty sandy gravelly CLAYDepth (m): -

BS1377 : Part 2 : Clause 9.2 : 1990 Wet Sieving MethodBS1377 : Part 2 : Clause 9.4 : 1990 Sedimentation by the Pipette Method

SIEVE

Sieve % pass

200 mm 100

125 mm 100

90 mm 100

75 mm 100

63 mm 100

50 mm 100

37.5 mm 100

28 mm 96

20 mm 94

14 mm 92

10 mm 86

6.3 mm 79

5 mm 76

3.35 mm 73

2 mm 69

1.18 mm 66

600 µm 61

425 µm 56 Particle Proportions

300 µm 47 Cobbles 0.0 %

212 µm 40 Gravel 30.8 %

150 µm 36 Sand 37.2 %

63 µm 32 Silt 16.8 %

Clay 15.2 %

PIPETTE

Particle size % pass

20.0 µm 31

6.0 µm 23

2.0 µm 15Preparation:

No Pre-treatment used

Temp (°C) 20



Initials: Project Name: GEOLABS ®

SB 907BRI

Date: 09/03/2011


Authorised Signatories: • J R Masters (Qual Mgr) • C F Wallace (Tech Mgr) • G J Corio (Tech Mgr) • J Sturges (Tech Mgr) [X] S Burke (Snr Tech) GEOLABS®

Client: Vertase FLI Limited, Number One, Middle Bridge Business Park, Bristol Road, Portishead BS20 6PN

0.001 0.01 0.1 1 10 1000

10

20

30

40

50

60

70

80

90

100

Particle Size (mm)

Per

cent

age

Pas

sing

SILT

CLA

Y

0.001 0.01 0.1 1 10 1000102030405060708090100

Fine CoarseMedium Fine CoarseMedium Fine CoarseMedium

SAND GRAVEL

CO

BB

LES

SILT

CLA

Y

BS1377 : Part 2 : Clause 9 : 1990


Borehole Number: TB124 Description:Sample Number: - Brown clayey SAND and GRAVELDepth (m): -

BS1377 : Part 2 : Clause 9.2 : 1990 Wet Sieving Method

SIEVE

Sieve % pass

200 mm 100

125 mm 100

90 mm 100

75 mm 100

63 mm 100

50 mm 100

37.5 mm 100

28 mm 96

20 mm 87

14 mm 80

10 mm 74

6.3 mm 67

5 mm 64

3.35 mm 60

2 mm 57

1.18 mm 52

600 µm 47


300 µm 28 Cobbles 0.0 %

212 µm 18 Gravel 42.7 %

150 µm 14 Sand 46.2 %

63 µm 11 Silt & Clay 11.1 %




SB 907BRI

Date: 09/02/2011




0.001 0.01 0.1 1 10 1000102030405060708090100


SILT SAND GRAVEL

CO

BB

LES

CLA

Y

0.001 0.01 0.1 1 10 1000

10

20

30

40

50

60

70

80

90

100

Particle Size (mm)

Per

cent

age

Pas

sing

BS1377 : Part 2 : Clause 9 : 1990


Borehole Number: TB127 Description:Sample Number: - Brown clayey gravelly SANDDepth (m): -

BS1377 : Part 2 : Clause 9.2 : 1990 Wet Sieving Method

SIEVE

Sieve % pass

200 mm 100

125 mm 100

90 mm 100

75 mm 100

63 mm 100

50 mm 100

37.5 mm 100

28 mm 100

20 mm 99

14 mm 97

10 mm 93

6.3 mm 88

5 mm 86

3.35 mm 82

2 mm 76

1.18 mm 72

600 µm 65


300 µm 35 Cobbles 0.0 %

212 µm 21 Gravel 23.8 %

150 µm 17 Sand 62.7 %

63 µm 13 Silt & Clay 13.5 %




SB 907BRI

Date: 09/02/2011




0.001 0.01 0.1 1 10 1000102030405060708090100


SILT SAND GRAVEL

CO

BB

LES

CLA

Y

0.001 0.01 0.1 1 10 1000

10

20

30

40

50

60

70

80

90

100

Particle Size (mm)

Per

cent

age

Pas

sing

BS1377 : Part 4 : 1990

Moisture Content / Dry Density Relationship

Description:

Sample No: TB 5 Grey brown silty very sandy gravelly CLAY

BS1377 : Part 4 : Clause 3.4.4.1 : 1990 2.5 kg Compaction Test

Sample Preparation: Material was air dried. Single sample

Particles greater than 37.5mm were removed.

Particle Density: 2.69 (measured by small pyknometer method)

Material Retained

on 20 mm test sieve: 8 %

on 37.5 mm test sieve: 2 %

Maximum Dry Density 1.89 Mg/m³

Optimum Moisture Content 13 %




JS HAUXTON

Date:26/04/2011 907BRI


Authorised Signatories: � J R Masters (Qual Mgr) � C F Wallace (Tech Mgr) � G J Corio (Tech Mgr) [X] J Sturges (Tech Mgr) � S Burke (Snr Tech) GEOLABS®


6 8 10 12 14 16 18

1.75

1.80

1.85

1.90

1.95

Moisture Content (%)

Dry

De

nsity

(Mg

/m³)

0% air voids

5% air voids

10% air voids

BS1377 : Part 4 : 1990


Description:

Sample No: TB26 Grey silty sandy CLAY with rare fine

to medium gravel and chalk fragments



No particles were removed


Material Retained








JS HAUXTON

Date:26/04/2011 907BRI




10 15 20 25

1.55

1.60

1.65

1.70


Dry

De

nsity

(Mg

/m³)

0% air voids

5% air voids

10% air voids

Project Name: PROJECT 907BRI Date 07/04/2011

Approved J STURGES Project Number: GEO / 16715 Page 1 of 1

Bulk Dry Moisture Particle Density Saturation Voids Porosity Degree of

Borehole Sample Depth Density Content (Mg/m³) Moisture Content Ratio (Total Vol of Voids) Saturation Description

Number Number (m) Mg/m³ % (Measured) (Assumed) (%) (%) (%)

- TB9 - 2.03 1.68 20.8 2.73 22.60 0.622 0.384 91.3 Firm brown sandy silty CLAY with rare fine to medium gravel

- TB10 - 2.04 1.70 19.7 2.71 21.70 0.594 0.373 89.9 Firm brown sandy silty gravelly CLAY,

gravel is fine to medium grained

DENSITY, MOISTURE CONTENTS, POROSITY RESULTS GEOLABS ®

Test Report by GEOLABS Limited Bucknalls Lane, Garston, Watford, Hertfordshire, WD25 9XX (Ref 4640.402801) Page 1 of 1

Authorised Signatories: [ ] J R Masters (Qual Mgr) [ ] C F Wallace (Tech Mgr) [x] J Sturges (Tech Mgr) [ ] S Burke (Snr Tech) DensPoros.WK4 ISSUE 1 (02/10)

Client: Vertase FLI Limited, Number One, Middle Bridge Business Park, Bristol Road, Portishead BS20 6PN GEOLABS LIMITED ®

BS1377 : Part 6 : Clause 6 :1990

Determination of Permeability in a Triaxial Cell

Borehole / TP: Description:Sample No: TB4 Brown sandy gravelly CLAY, gravel is fine to coarse sand is fine toDepth: coarse

SPECIMEN DETAILS

Depth within original sample N/A

Orientation within original N/A Specimen preparation Remoulded using 4.5kg effort at natural moisture content

TEST DETAILS

Cell Preparation Performed in accordance with Clause 3.5

INITIAL FINAL

Diameter mm 104.5 104.4

Height mm 115.3 115.1

Moisture Content % 13 14Bulk Density Mg/m³ 2.21 2.23

Dry Density Mg/m³ 1.96 1.96

SATURATION STAGE

Saturation initially by constant moisture content, followed by back-pressure assistance using 5-10 kPa differential

'B' value 0.79 0.92

CONSOLIDATION STAGE

Effective pressure kPa 50

Volume change mL 4.2

PERMEABILITY STAGE

Pressure difference across specimen 10 Coefficient of permeability at 20ºC =

Mean effective stress kPa 45

1.3 x 10 m/s TEST DURATIONS

Saturation days 3 Hydraulic Gradient = 8.9Consolidation days 2 Flow days 2


Approved GEO / 16801Initials: Project Name: GEOLABS

PTH HAUXTON 907BRIDate:

09/05/11 Schedule 5


Authorised Signatories: [ ] J R Masters (Qual Mgr) [ ] C F Wallace (Tech Mgr) [X] P T Heritage (Tech Mgr) [ ] J M M Powell (Tech Dir)

Client: Vertase FLI Limited, Number One, Middle Bridge Business Park, Bristol Road, Portishead BS20 6PN GEOLABS ®

0 500 1000 1500 20000

0.2

0.4

0.6

0.8

1

1.2

1.4

Time (min)

Cum

ulat

ive

Flo

w (

mL)

0

0.2

0.4

0.6

0.8

1

1.2

-10

®

BS1377 : Part 6 : Clause 6 :1990


Borehole / TP: Description:Sample No: TB5 Grey silty CLAY and fine gravelDepth:

SPECIMEN DETAILS

Depth within original sample

Orientation within original Specimen preparation Remoulded @ NMC using 4.5kg compactive effort

TEST DETAILS


INITIAL FINAL


Height mm 116.2 115.9



SATURATION STAGE


'B' value 0.50 0.96

CONSOLIDATION STAGE



PERMEABILITY STAGE






Approved GEO /16761Initials: Project Name: GEOLABS

PTH HAUXTONDate:

28/04/11 907BRI


Authorised Signatories: [ ] J R Masters (Qual Mgr) [ ] C F Wallace (Tech Mgr) [X] P T Heritage (Ops Mgr) [ ] J M M Powell (Tech Dir)


0 500 1000 1500 20000

0.2

0.4

0.6

0.8

1

Time (min)

Cum

ulat

ive

Flo

w (

mL)

0

0.2

0.4

0.6

0.8

1

1.2

-11

®

BS1377 : Part 6 : Clause 6 :1990


Borehole / TP: Description:Sample No: TB9 Light grey silty CLAY with occasional fine gravelDepth:

SPECIMEN DETAILS


Orientation within original N/A Specimen preparation Remoulded using a 2.5kg effort at NMC

TEST DETAILS


INITIAL FINAL


Height mm 115.2 114.3



SATURATION STAGE


'B' value 0.83 0.98

CONSOLIDATION STAGE



PERMEABILITY STAGE







PTH PROJECT 907BRIDate:

15/04/11




0 2000 4000 6000 8000 10000 120000

2

4

6

Time (min)

Cum

ulat

ive

Flo

w (

mL)

0

0.2

0.4

0.6

0.8

1

1.2

-10

®

BS1377 : Part 6 : Clause 6 :1990


Borehole / TP: Description:Sample No: TB10 Grey silty CLAY with occasional fine to medium gravelDepth:

SPECIMEN DETAILS


Orientation within original N/A Specimen preparation Remoulded using a 2.5kg effort at NMC

TEST DETAILS


INITIAL FINAL


Height mm 114.6 113.8



SATURATION STAGE


'B' value 0.85 0.96

CONSOLIDATION STAGE



PERMEABILITY STAGE







PTH PROJECT 907BRIDate:

15/04/11



Client: GEOLABS ®

0 2000 4000 6000 8000 10000 12000-2

0

2

4

6

8

Time (min)

Cum

ulat

ive

Flo

w (

mL)

0

0.2

0.4

0.6

0.8

1

1.2

-10

®

BS1377 : Part 6 : Clause 6 :1990


Description:Sample No: TB13 Soft to firm light grey silty CLAY

SPECIMEN DETAILS


Orientation within original Vertical Specimen preparation remoulded using 4.5kg effort at NMC

TEST DETAILS


INITIAL FINAL


Height mm 114.3 112.2



SATURATION STAGE


'B' value 0.98 1.03

CONSOLIDATION STAGE



PERMEABILITY STAGE







PTH 907BRIDate:

02/03/11




0 1000 2000 3000 4000 50000

1

2

3

Time (min)

Cum

ulat

ive

Flo

w (

mL)

0

0.2

0.4

0.6

0.8

1

1.2

-10

®

BS1377 : Part 6 : Clause 6 :1990


Description:Sample No: TB19 Soft light grey silty CLAY with occasional fine to medium gravel (wet sample)

SPECIMEN DETAILS


Orientation within original Vertical Specimen preparation Remoulded using a 4.5kg effort

TEST DETAILS


INITIAL FINAL


Height mm 112.1 109.9



SATURATION STAGE


'B' value 1.00 1.00

CONSOLIDATION STAGE



PERMEABILITY STAGE







PTH 90 BRIDate:

02/03/11




0 2000 4000 60000

2

4

6

8

Time (min)

Cum

ulat

ive

Flo

w (

mL)

0

0.2

0.4

0.6

0.8

1

1.2

-10

®

BS1377 : Part 6 : Clause 6 :1990


Borehole / TP: Description:Sample No: TB26 Light grey silty CLAY with occasional fine gravelDepth:

SPECIMEN DETAILS

Depth within original sample

Orientation within original Specimen preparation Remoulded @ NMC using a compactive effort of 4.5kg

TEST DETAILS


INITIAL FINAL


Height mm 116.3 115.4



SATURATION STAGE


'B' value 0.92 0.96

CONSOLIDATION STAGE



PERMEABILITY STAGE






Approved GEO /16761Initials: Project Name: GEOLABS

PTH HAUXTONDate:

28/04/11 907BRI




0 500 1000 1500 20000

0.5

1

1.5

2

Time (min)

Cum

ulat

ive

Flo

w (

mL)

0

0.2

0.4

0.6

0.8

1

1.2

-10

®

BS1377 : Part 6 : Clause 6 :1990


Description:Sample No: TB32 Soft to firm light grey slightly sandy CLAY with occational fine to medium gravel

SPECIMEN DETAILS


Orientation within original Vertical Specimen preparation Remoulded using a 4.5kg effort

TEST DETAILS


INITIAL FINAL


Height mm 115.6 114.6



SATURATION STAGE


'B' value 0.96 1.00

CONSOLIDATION STAGE



PERMEABILITY STAGE







PTH 907BRIDate:

02/03/11




0 1000 2000 3000 4000 50000

0.5

1

1.5

2

2.5

Time (min)

Cum

ulat

ive

Flo

w (

mL)

0

0.2

0.4

0.6

0.8

1

1.2

-10

®

BS1377 : Part 4 : 1990


Trial Pit No: TB 66 Description:

Grey silty CLAY





Material Retained








JS 907BRI

Date:28/03/2011




5 10 15 20 25 30

1.50

1.55

1.60

1.65

1.70


Dry

De

nsity

(Mg

/m³)

0% air voids

5% air voids

10% air voids

BS1377 : Part 4 : 1990



Grey silty CLAY with rare iron pyrite





Material Retained








JS 907BRI

Date:28/03/2011


Authorised Signatories: � J R Masters (Qual Mgr) � C F Wallace (Tech Mgr) � G J Corio (Tech Mgr) � J Sturges (Tech Mgr) � R J Platt (Snr Tech) � J J M Powell (Tech Dir) GEOLABS®


0 10 20 30

1.50

1.55

1.60

1.65

1.70


Dry

De

nsity

(Mg

/m³)

0% air voids

5% air voids

10% air voids

BS1377 : Part 4 : 1990



Grey silty CLAY





Material Retained








JS 907BRI

Date:28/03/2011




5 10 15 20 25 30

1.50

1.55

1.60

1.65

1.70


Dry

De

nsity

(Mg

/m³)

0% air voids

5% air voids

10% air voids

BS1377 : Part 4 : 1990



Grey silty CLAY with rare fine gravel





Material Retained








JS 907BRI

Date:28/03/2011




5 15 25 35

1.40

1.50

1.60

1.70


Dry

De

nsity

(Mg

/m³)

0% air voids

5% air voids

10% air voids

Documents

Former Bayer Crop Science Site Hauxton Cambridgeshire June