lidl uk gmbh geo-environmental investigation report · lidl development and an existing small area...

Lidl UK GmbH

Geo-Environmental Investigation Report Daniels Lane, St Austell

February 2016

Lidl UK GmbH

Geo-Environmental

Investigation Report

Daniels Lane, St Austell

February 2016

© Opus International Consultants (UK) Ltd 2016

Prepared By

Opus International Consultants (UK) Ltd

Birmingham Office

S3, 3800 Parkside, Birmingham Business Park

Craig Bulga Birmingham, B37 7YG

Senior Environmental Scientist United Kingdom

Reviewed By

Telephone: +44 121 329 1560

Facsimile: +44 121 788 0757

Phil Edge Date: February 2016

Geo-Environmental Workgroup Manager Reference: CAB/J-B0950.00 (R01)

Status: Final

Approved for

Release By

Phil Edge

Geo-Environmental Workgroup Manager

CAB/J-B0950.00 (R01) Geo-Environmental Investigation


i


Contents

A Factual Information ........................................................................................... 1

1 Introduction ....................................................................................................... 1

1.1 Instruction ......................................................................................................................... 1 1.2 Objective............................................................................................................................ 1 1.3 Limitations ........................................................................................................................ 2

2 The Site .............................................................................................................. 3 2.1 Location and Access .......................................................................................................... 3 2.2 Description ........................................................................................................................ 3

3 Desk Study ......................................................................................................... 4 3.1 Introduction ...................................................................................................................... 4 3.2 History ............................................................................................................................... 4 3.3 Geology, Hydrogeology and Hydrology ............................................................................ 6 3.4 Environmental Considerations ......................................................................................... 7

3.5 Radon .............................................................................................................................. 10 3.6 Coal Mining ...................................................................................................................... 11 3.7 Summary of Previous Ground Investigation Reports ...................................................... 11

3.8 Local Water Authority Search ......................................................................................... 12

4 Preliminary Conceptual Site Model ................................................................... 13 4.1 Background ..................................................................................................................... 13 4.2 Potential Sources of Contamination ............................................................................... 14 4.3 Potential Migration Pathways ......................................................................................... 14 4.4 Potential Receptors of Contamination ............................................................................ 15 4.5 Pollutant Linkages and Environmental Risks ................................................................ 15

5 Japanese Knotweed Survey ............................................................................... 17 5.1 Introduction .................................................................................................................... 17 5.2 Background ..................................................................................................................... 17 5.3 Methodology ................................................................................................................... 18 5.4 Results ............................................................................................................................. 18 5.5 Conclusion ....................................................................................................................... 18

6 Investigation Methodology ................................................................................19

6.1 Objectives ........................................................................................................................ 19 6.2 Clearance of Underground Services ................................................................................ 19 6.3 Exploratory Holes ........................................................................................................... 19 6.4 Logging and Sampling .................................................................................................... 19 6.5 Chemical Testing ............................................................................................................. 20 6.6 Geotechnical Testing ....................................................................................................... 20 6.7 Gas/Groundwater Monitoring ........................................................................................ 20



ii


7 Investigation Results ........................................................................................ 22 7.1 Introduction .................................................................................................................... 22 7.2 Strata Observations ......................................................................................................... 22

7.3 Standard Penetration Tests (SPT’s) ................................................................................ 23 7.4 Groundwater Observations ............................................................................................. 23 7.5 Evidence of Potential Ground Contamination ................................................................ 23 7.6 Chemical Testing Results ................................................................................................ 23 7.7 Geotechnical Testing Results .......................................................................................... 25

7.8 Ground Gas/Groundwater Monitoring Results .............................................................. 26

B Assessment & Recommendations ..................................................................... 27

8 Environmental Assessment .............................................................................. 27 8.1 Soil ................................................................................................................................... 27

8.2 Ground Gas ..................................................................................................................... 28 8.3 Revised Conceptual Site Model ....................................................................................... 28 8.4 Health & Safety ............................................................................................................... 29 8.5 Waste Disposal ................................................................................................................ 29 8.6 Liaison with Regulators .................................................................................................. 30 8.7 Water Supply Pipes ......................................................................................................... 30 8.8 Environmental Protection ............................................................................................... 30

9 Geotechnical Assessment .................................................................................. 31 9.1 Discussion ....................................................................................................................... 31 9.2 Foundation Design .......................................................................................................... 32

9.3 Floor Slab Design ............................................................................................................ 33 9.4 Pavement Design ............................................................................................................. 33

9.5 Construction .................................................................................................................... 33 9.6 Concrete Specification .................................................................................................... 33 9.7 Soakaways ....................................................................................................................... 34 9.8 Retaining Wall ................................................................................................................. 34

10 Recommendations ........................................................................................... 35

Figures

J-B0950.00/G001-A Site Location Plan

J-B0950.00/G002-A Exploratory Hole Location Plan

14053 / AD 110 Proposed Site Layout Plan

Appendices

Appendix A Historical Maps

Appendix B Environmental Database Report

Appendix C Underground Assets Information Report

Appendix D Exploratory Hole Records

Appendix E Chemical Testing Results

Appendix F Geotechnical Testing Results

Appendix G Gas and Groundwater Monitoring Results

Appendix H Human Health Assessment Criteria



1 Opus International Consultants (UK) Ltd

A Factual Information

1 Introduction

1.1 Instruction

1.1.1 Opus International Consultants (Opus) were instructed by Lidl UK (The Client) to carry out

a Geo-Environmental Investigation of a site at Daniels Lane, St Austell.

1.1.2 The site was formerly occupied by an Automatic Controls Factory, and more recently by a

Builders Merchants. The site building and other structures associated with these former site

uses have been demolished and cleared to ground level. The site is currently an open, vacant

plot of land.

1.1.3 Lidl propose to redevelop the site with the construction of a new food store in the north, a

delivery area to the north-east and car parking areas to the south-west and south-east. An

existing access point in the southern corner of the site will be utilised for the proposed new

Lidl development and an existing small area of soft landscaping in the western corner will be

redeveloped as part of the site proposals. It is also understood from the provided information

that an existing retaining wall running along the south-eastern site boundary will be removed

and replaced with a graded, landscaped bank. The Proposed Site Layout is detailed on the

appended One Design Architectural Services drawing (referenced 14053 / AD 110 and dated

January 2016).

1.1.4 A previous ground investigation of the site was undertaken for the neighbouring Tesco store

when they were looking to expand their car parking area onto the site in 2010. Several

corresponding reports were produced for environmental and geotechnical assessments.

1.1.5 The following reports have been supplied to, and reviewed, by Opus:

(a) Delta Simons Combined Phase I/II Environmental Assessment Report, referenced 10-3093.02, dated July 2010

(b) Geotechnics Ground Investigation Report, referenced PE100810, dated July 2010

1.1.6 This report should be read in conjunction with the above listed reports.

1.2 Objective

1.2.1 The objective of this Geo-Environmental Investigation is to provide additional coverage and

testing across the site in order to complete updated environmental and geotechnical

assessments of the underlying ground conditions. This will then provide a robust data set to

assess potential contamination risks and liabilities associated with the ownership and

development of the site and recommend suitable foundation, floor slab, highway design

options for the proposed new Lidl development.




1.3 Limitations

1.3.1 This report has been prepared by Opus with all reasonable skill and care within the terms of

the Contract with the Client, Lidl UK, and taking account of the information made available

by the Client, as well as the manpower and resources devoted to it by agreement with the

Client. Opus disclaims any responsibility to the Client and others in respect of any matters

outside the scope of the above Contract.

1.3.2 This report has been produced on behalf of the Client and no responsibility is accepted to any

Third Party for all or any part. This report should not be relied upon or transferred to any

other parties without the express written authorisation of Opus. If any unauthorised Third

Party comes into possession of this report, they rely on it at their own risk and the authors

owe them no duty of care or skill.

1.3.3 The desk study information has been obtained from a variety of sources, which Opus believes

are reliable. Nevertheless, Opus cannot and does not guarantee the authenticity or reliability

of the information it has relied upon from these sources.

1.3.4 Whilst this report may express an opinion on the possible configuration of strata,

groundwater, ground gas and contaminants between or beyond exploratory hole positions or

on the possible presence of features based on either visual, verbal or published evidence, this

is for guidance only, and no liability can be accepted for its accuracy.

1.3.5 The comments on groundwater and ground gas conditions are based on observations made

at the time of the investigation. It should be noted, however, that groundwater levels and

ground gas concentrations may vary from those reported due to seasonal or other effects.

1.3.6 The exploratory holes were positioned across the site in order to provide adequate coverage

and to target any potential sources of contamination identified during the desk study and site

observations. The positions were located approximately and no guarantee can be given as to

their accuracy on the appended site plans.

1.3.7 The site plans appended to this report should not be used for scaling purposes.




2 The Site

2.1 Location and Access

2.1.1 The site is located in Holmbush on the eastern edge of St Austell, Cornwall and lies

approximately 2km east of the town centre. The site location, shown on the appended Site

Location Plan (Drawing No. J-B0950.00/G001-A) is centred on National Grid

Reference 203630, 525900.

2.1.2 The site is accessed from Daniels Lane in the southern corner.

2.2 Description

2.2.1 The following section describes the site at the time of our investigation in January 2016.

2.2.2 The site was formerly occupied by an Automatic Controls Factory, and more recently by a

Builders Merchants. The site building and other structures associated with these former site

uses have been demolished and cleared to ground level.

2.2.3 The site is currently an open, vacant plot of land. The majority of it comprises the concrete

slab of the former site building footprint. Tarmacadam-surfaced areas representing a former

visitor car parking area, staff car parking area and rear storage yard are present to the south-

west, south-east and north-east of the concrete slab respectively. The car parking areas were

being used by staff working in the neighbouring Tesco store at the time of our investigation.

Heras fencing had been erected across the south-east of the site to partition these car parking

areas from the remainder of the site. A small area of soft landscaping is present in the western

corner of the site fronting Daniel Lane. This consists of several semi-mature trees, patches

of bramble scrub and rank grass. A gas governor station is present beside the access point in

the southern corner of the site.

2.2.4 The majority of the site is level and flat, however, ground levels rise steeply by approximately

5.0-6.0 metres in a north-westerly direction within the small area of soft landscaping. The

site is at an elevated level in comparison to the neighbouring Tesco site to the south-east, and

is retained by a wall of concrete block construction running along its south-eastern site

boundary. Ground levels on the Tesco site appear to fall gently in an easterly direction. As

such, the southern corner of the site is approximately 2.0 metres higher than land

immediately to the south-east, however, the eastern corner is approximately 4.0 metres

higher.

2.2.5 The site is bound to the south-west by Daniels Lane, with residential properties beyond, to

the south-east by the Tesco site and to the north-east and north-west by various commercial

/ light industrial premises on Holmbush Industrial Estate.




3 Desk Study

3.1 Introduction

3.1.1 The following sources of information have been consulted as part of the desk study:

(a) Opus Archives (b) Landmark Information Group Ltd ‘Envirocheck’ database report (c) Selected County Series and Ordnance Survey plans (d) British Geological Survey 1:50,000 Map, Bodmin (Sheet 347) and BGS online Lexicon (e) Environment Agency Website (f) BR 211 Radon; Guidance on Protective Measures for New Dwellings, 2007 Edition (g) Law Society Guidance Notes and Directory for Coal Mining Searches

3.2 History

3.2.1 A review of the site history has been undertaken in order to identify any previous potentially significant contaminative activities, located either on-site or off-site. This is summarised in Table 3.1.

3.2.2 Potential on-site contamination sources may present a risk to future site users and underlying and/or adjacent ‘controlled waters’. Neighbouring potential off-site contamination sources may also present a risk to soils and, if present, groundwater underlying the site through cross boundary migration or deposition of waste materials.

3.2.3 The history of the site is recorded over selected periods by inspected maps, copies of which are presented in Appendix ‘A’. The account presented in this report is restricted by specific time periods represented by these maps only.

Table 3.1 Site History

Map Edition Key Features

On Site Off Site

1882 (1:2,500) The site is shown as undeveloped farmland, comprising part of three fields.

Daniels Lane is shown immediately to the south-west.

A stream, broadly flowing in an easterly direction, is shown to the south-east of the site. A Ford is shown where Daniels Lane crosses the stream immediately adjacent to the south-west corner of the site.

Two Shafts are shown immediately beyond Daniels Lane.

Another Shaft is shown approximately 130m north and a further Shaft is shown approximately 250m north-west.

The immediate surrounding area generally comprises farmland.

A large mine complex consisting of Shafts, a Smithy and Spoil Heaps is shown approximately 300m north-east.





On Site Off Site

1888 (1:10,560) No significant changes recorded. The large mine complex is labelled as West Wheal Eliza Tin Mine.

An Iron Foundry, Naphtha Works and Smithing Works are shown approximately 400-500m south-west.

1907-08 (1:2,500 & 1:10,560)

No significant changes recorded. A Bridge is shown where Daniels Lane crosses the stream immediately adjacent to the south-west corner of the site.

An unidentified building complex is shown approximately 80-100m south-east beyond the stream.

The three nearby Shafts are no longer shown. A Spoil Heap is shown immediately beyond Daniels Lane.

The West Wheal Eliza Tin Mine is labelled as ‘Disused’.

1933

(1:2,500 & 1:10,560)

No significant changes recorded. No significant changes recorded.

The unidentified building complex is labelled as Sawmills.

1938 (1:10,560) No significant changes recorded. No significant changes recorded.


1968-70 (1:2,500 & 1:10,000)

No significant changes recorded. No significant changes recorded.

Residential development is shown immediately beyond Daniels Lane to the west and north-west.

An Engineering Works is shown approximately 50m north-west.

Commercial / light industrial development is shown approximately 100m north and east including a Clothing Factory, Plastics Factory and Stationery Factory.

The Sawmills are labelled as including a Box Factory.

1975-77

(1:2,500 & 1:10,000)

The former Automatic Controls Factory is shown to occupy the site including the main building, car park and rear storage yard.

Further residential development is shown beyond Daniels Lane to the south-west.

The Engineering Works is shown to have been significantly extended to the north-east.

Further commercial / light industrial development is shown approximately 80-100m north and east including a Joinery Works, Heavy Vehicle Depot and Warehouse. These developments are labelled as Holmbush Industrial Estate.

1992-94 (1:2,500 & 1:10,000)

No significant changes recorded. The Sawmills and Box Factory are no longer shown. An unidentified complex of commercial / light industrial-type buildings is shown to the south-east.

The Joinery Works is shown to have been significantly extended to the south-west.





On Site Off Site

2006 (1:10,000) No significant changes recorded. The unidentified complex of commercial / light industrial-type buildings is no longer shown. The existing Tesco store, car park, petrol filling station and partially culverted stream are shown to the south-east.


3.3 Geology, Hydrogeology and Hydrology

Geology

3.3.1 The general geology of the area is shown on the British Geological Survey 1:50,000 Sheet 314 and is summarised in Table 3.2.

Table 3.2 Geology

Stratigraphic

Name Age Type Description

Alluvium Quaternary Superficial

Deposits

Clay, Silt, Sand and Gravel

Meadfoot Group Devonian Bedrock Dark Shales and Siltstones with sporadic grey-

brown Sandstones and shell debris. Exhibits

red colouration locally

3.3.2 Given the previous developed nature of the site and the presence of the retaining wall along the south-eastern site boundary, Made Ground is considered likely to be present beneath the site. BGS Recorded Mineral Sites

3.3.3 There is one BGS Recorded Mineral Site within 1km of the site as follows:

Table 3.3 BGS Recorded Mineral Site

Name Distance &

Direction from Site Type Commodity Status

Boscoppa Mine 934m North-east Opencast Slate Ceased

BGS Estimated Soil Chemistry

3.3.4 The Envirocheck report provides a summary of the estimated soil chemistry for the site and surrounding area with background concentration ranges for Arsenic, Cadmium, Chromium, Lead and Nickel. The estimated ranges are summarised as follows:

Arsenic = 35-45mg/kg

Cadmium = <1.8mg/kg

Chromium = 60-90mg/kg

Lead = <150mg/kg

Nickel = 15-30mg/kg




Hydrogeology

3.3.5 The Environment Agency classifies both the Alluvium and the Meadfoot Group underlying

the site as Secondary ‘A’ Aquifers.

3.3.6 Secondary ‘A’ Aquifers (formerly Minor Aquifers) are permeable sediments or fissured rocks

that are capable of storing and yielding water at a local rather than strategic scale, and

support local water supplies and base flow to rivers.

3.3.7 The site is not recorded as being within a Groundwater Source Protection Zone.

3.3.8 There are no Groundwater Abstractions recorded within 1km. Twelve Groundwater

Abstractions are recorded between 1km and 2km from the site, which are generally for

agricultural spray irrigation and industrial processing (quarrying).

Hydrology

3.3.9 The nearest surface watercourse to the site is the stream that runs through the adjoining Tesco site to the south-east. The stream broadly flows in an easterly direction but it has been re-routed slightly to the south to accommodate the petrol filling station. It lies in a closed culvert where it is bridged at two points by the access road however it lies in an open channel where it passes to the south of the petrol filling station and the north of the store. The stream lies immediately adjacent to both the south-western and south-eastern corners of the site at its closest point but lies approximately 50m south where it runs through the Tesco site.

3.3.10 There is one recorded Surface Water Abstraction within 1km of the site as follows:

Table 3.4 Surface Water Abstractions

Distance & Direction from Site

Operator Abstraction

881m West People 2000 Ltd General Washing / Process Water

3.3.11 The Environment Agency assesses that the site itself is not at risk of flooding from rivers or seas. Land immediately to the south-east of the site is at risk of extreme flooding from rivers or seas.

3.4 Environmental Considerations

3.4.1 The ‘Envirocheck’ database report comprises a summary of statutory data held on public

registers which can be used to identify potential sources of contamination on the site and

within a search radius of 1km. In addition, the report also contains data which can be used

to identify potential receptors of contamination on the site and within 1km.

3.4.2 Specific details relating to the environmental setting of the site are presented within the

Environmental Database Report presented in Appendix ‘B’. The salient issues which relate

to the site are summarised in the following sections.




Discharge Consents 3.4.3 There are five recorded Discharge Consents within 250m of the site as follows:

Table 3.5 Discharge Consents

Operator Distance &

Direction from Site

Discharge Type Receiving Water Status

South West Water 26m

South-west

Storm Water

Overflow

Sandy (Crinnis)

River

Varied


South-west

Storm Sewage

Overflow

Sandy (Crinnis)

River

Modified


South-west

Storm Effluent Sandy (Crinnis)

River

Not Supplied

Tesco Stores Ltd 62m South-east Site Drainage Sandy River Varied

Tesco Stores Ltd 92m East Site Drainage Sandy River Varied

Local Authority Pollution Prevention and Controls

3.4.4 There is one recorded Local Authority Pollution Prevention and Control authorised processes within 250m of the site as follows: Table 3.6 Local Authority Pollution Prevention and Controls

Name Distance & Direction

from Site Description Status

Tesco Filling Station 32m South PG1/14 Petrol filling

station

Authorised

Pollution Incidents to Controlled Waters 3.4.5 There are thirteen recorded Pollution Incidents to Controlled Waters within 250m of the site

as follows: Table 3.7 Pollution Incidents to Controlled Waters

Severity Distance &

Direction from Site Date Pollutant Cause

Category 2 -

Major Incident

37m South 07/11/95 Storm Overflow:

Crude Sewage

Effluent Discharge

Category 3 -

Minor Incident

42m South 24/02/99 Discolouration Not Given

Category 3 -

Minor Incident

70m West 03/02/93 Storm Overflow:

Storm Sewage

Overflow

Category 3 -

Minor Incident

86m South-west 24/07/91 Storm Overflow:

Crude Sewage

Overflow

Category 3 -

Minor Incident

87m South-east 10/12/91 Road Collision:

Waste Oil

Leakage




Severity Distance &

Direction from Site Date Pollutant Cause

Category 3 -

Minor Incident

88m South-west 08/08/92 Storm Overflow:

Crude Sewage

Overflow

Category 3 -

Minor Incident

97m North-east 19/05/93 Industrial:

Chemicals

Inadequate

Design/Capacity

Category 3 -

Minor Incident

114m South-west 16/01/91 Mine Workings:

Process Water

Burst

Category 3 -

Minor Incident

124m South-east 11/05/91 Storm Overflow:

Crude Sewage

Overflow

Category 3 -

Minor Incident

212m East 14/06/91 Not Given Not Given

Category 3 -

Minor Incident

230m East 23/10/92 Not Given Not Given

Category 3 -

Minor Incident

232m East 13/08/91 Paper & Printing:

Process Water

Poor Operational

Practice

Category 3 -

Minor Incident

239m North-east 15/07/91 Building Site:

Vehicles

Inadequate

Design/Capacity

3.4.6 It should be noted that records for pollution incidents to controlled waters since

approximately 2000 are not readily available in the commercial domain.

Historical Landfill Sites 3.4.7 There is one recorded Historical Landfill Site within 1km of the site as follows:

Table 3.8 Historical Landfill Sites

Name Distance & Direction

from Site Input Dates Waste Type

Nettles Corner 818m East First input date not given

Last input date

December 1980

Not Given

Notification of Installations Handling Hazardous Substances (NIHHS) Sites

3.4.8 There is one recorded NIHHS Site within 1km of the site as follows:

Table 3.9 NIHHS Sites

Name Distance & Direction from

Site Status

Mount Caravans Ltd 149m North Not Active




Contemporary Trade Directory Entries 3.4.9 There are 25 Contemporary Trade Directory Entries within 250m of the site as follows:

Table 3.10 Contemporary Trade Directory Entries

Classification Number Active Number Inactive

Garage Services 1 1

Greeting Card Publishers 1

General and Precision Engineers 1 2

Printers 1 2

Dry Cleaners and Laundrettes 1 1

Marine Engineers 1

Electronic Engineers 1

Lawnmower Sales and Service 1

UPVC Products Manufacturers and Suppliers 1

Chemists and Pharmacists 1

Commercial Vehicle Dealers 2

Mechanical Engineers 1

Glass Products Manufacturers 1

Fork Lift Trucks 2

Plastics Extrusion 1

Hydraulic Engineers 1

Fireplaces and Mantelpieces 1

Fuel Station Entries

3.4.10 There is one Fuel Station Entry within 250m of the site as follows: Table 3.11 Fuel Station Entries

Name Distance & Direction from

Site Status

Tesco 30m Open

3.5 Radon

3.5.1 Reference to the ‘Envirocheck’ database report and BR211: 2015 indicates that the site is in a

higher probability area where between 10% and 30% of homes are above the radon action

level and where full radon protective measures are necessary in the construction of new

buildings or extensions. Although BR211: 2015 relates specifically to residential properties,

an employer has a duty of care to protect its employees from exposure to significant levels of

radon, and maintain radon levels of less than 400 becquerels within commercial properties.




3.6 Coal Mining

3.6.1 St Austell is not listed in the Law Society’s Guidance Notes and Directory of Coal Mining Searches as a location that requires a Coal Mining Report.

3.7 Summary of Previous Ground Investigation Reports

3.7.1 The previous ground investigation of the site in 2010 comprised the advancement of a

number of exploratory holes including 6 no. window sample holes (WS1-WS6) and 4 cable

percussion boreholes (BH1-BH4). A further 3 no. cable percussion boreholes (BH5-BH7)

were also advanced on the neighbouring Tesco site to the south-east.

3.7.2 The ten exploratory holes across the site generally encountered hardstanding surfacing

underlain by granular Made Ground to depths ranging between 0.30m beneath the north-

west of the site and 2.70m begl beneath the south-east. Alluvium was locally present between

1.40m and 2.60m begl beneath the east of the site and natural strata belonging to the

Meadfoot Group was present beneath the Alluvium and the remainder of the site to maximum

proven depths ranging between 1.80m and 4.00m begl.

3.7.3 Standard Penetration Tests (SPT’s) gave ‘N’ values ranging between 2 and 26 in the Made

Ground, 0 and 21 in the Alluvium and 16 and >50 in the Meadfoot Group strata.

3.7.4 Groundwater strikes were observed at depths between 2.20m and 4.50m begl during drilling. During monitoring, standing groundwater levels were observed at depths between approximately 3.00m and 4.50m begl.

3.7.5 No visual or olfactory evidence of ground contamination (i.e. staining or odour) was noted

during the intrusive investigation. The results of chemical testing of soil samples revealed an elevated arsenic concentration of 690mg/kg in the WS6 0.60m sample and a potentially significant total C5-C35 TPH concentration of 3,300mg/kg in the WS3 1.70m sample.

3.7.6 Leachate tests identified no leachable concentrations of potential contaminants of concern

within soils beneath the site and the results of chemical testing of groundwater samples revealed no significant concentrations of potential contaminants of concern within groundwater beneath the site.

3.7.7 Moisture content values ranged between 25% and 53% in the Alluvium and 13% and 25% in

the Meadfoot Group strata. Plasticity index values determined through Atterburg Limit test data indicated both the Alluvium and the Meadfoot Group to be non-plastic. Particle Size Distribution (PSD) values indicated the Made Ground to generally comprise significant proportions of gravel and cobbles, the Alluvium to generally comprise silty gravel and the Meadfoot Group strata to generally comprise variably clayey, silty, sandy gravel.

3.7.8 The results of four gas monitoring visits recorded no methane concentrations above the

instrument detection limit (<0.1% v/v), a peak carbon dioxide concentration of 5.3% v/v and no gas flow.




3.7.9 Historical tin and copper mines are recorded within the immediate area of the site. As such,

a specialist mining report by Cornwall Consultants was included as part of the previous

ground investigation works, which is summarised as follows:

The outcrop of the main Lode lies approximately 150 metres north-east of the site and therefore any associated unrecorded shallow workings would not present a risk of subsidence at the site;

Although other parallel lodes have been mined to the north of the main Lode, the mine plans do not indicate the presence of any other lodes to the south, in the vicinity of the site;

The 1882 edition of the Ordnance Survey map shows a line of Shafts running in a general north to south direction on the western side of Daniels Lane. The closest of these Shafts lie 10 metres and 20 metres west of the south-western site boundary. The same map also shows a ‘pump’ close to the junction of Daniels Lane and Holmbush Road to the south of the site. It is possible that this pump is sited on a former shaft. Cornwall Consultants believed that these shafts (and the pump) are air shafts associated with a drainage tunnel (adit) that served to drain surface water from the workings of the Charlestown United/West Wheal Eliza tin mines. The outlet of this adit lies at the north end of Charlestown Harbour.

A branch of the adit may have been driven in a north-east direction beneath the western corner of the site to connect with a shaft located 20 metres north of the site, although this is not confirmed by the records. Cornwall Consultants considered that the adit is likely to be of small cross-sectional area (typically 0.8 metres wide by 1.8 metres high) and estimated to lie at a depth of approximately 30 metres in this vicinity. Hence the adit was not considered by Cornwall Consultants to present a direct risk of subsidence to the site.

3.7.10 A small stand of Japanese knotweed (Fallopia japonica) was mapped by Aspect Ecology as

having been identified beside the gas governor station adjacent to the access point in the southern corner of the site in 2010. Further stands were also mapped at several locations across the neighbouring Tesco site.

3.8 Local Water Authority Search

3.8.1 A request was made to the local water authority, South West Water, for a search to obtain

information on all of their underground assets (i.e. water, drainage and sewerage) within the

immediate vicinity of the site in order to ascertain whether a leat (surface watercourse),

highlighted in the specialist mining report, passes through the western corner of the site. It

was believed to have been culverted and re-directed.

3.8.2 The Underground Assets Information Report provided by South West Water is presented in

‘Appendix C’.

3.8.3 The results of the local water authority search by South West Water have not revealed any

records to confirm the presence of the culverted leat or other similar underground features

beneath the site.




4 Preliminary Conceptual Site Model

4.1 Background

4.1.1 The Contaminated Land (England) Regulations provide a risk based approach to contaminated land in England. The government has adopted a ‘suitable for use’ criteria under the Regulations. This means that remediation is only required to the standard which is acceptable for the use of a site.

4.1.2 Land is only defined as ‘contaminated’ under the Regulations where it appears to the

regulatory authority that:

Significant environmental harm is being caused, or is likely to be caused; or

Significant pollution of controlled waters is being caused, or is likely to be caused.

4.1.3 Risk is defined as the combination of:

The probability, or frequency, of occurrence of a defined hazard; and

The magnitude (including the seriousness) of the consequences.

4.1.4 For a risk of environmental harm or pollution to occur as a result of contaminated land, all of

the following elements must be present:

A Source, i.e. a contaminant which could cause harm to health and/or the environment. Sources include current and historical uses, activities and events either on the site or in the surrounding area;

A Receptor, i.e. a target which could be harmed by the contaminant. Receptors include both human and non-human organisms, ‘controlled waters’ (groundwater and surface water) and building materials (concrete and plastic); and

A Pathway, i.e. a route by which contaminants could move from a source to a receptor.

4.1.5 A Pollutant Linkage occurs when a contaminant is able to move from a source, via a

pathway to a receptor. Each element may exist in isolation and pose no environmental risk. It is only when all three elements are linked to each other that a pollution linkage exists, and poses an environmental risk. If all three elements are present, then the magnitude of the risk is a function of the mobility of the source, the sensitivity of the receptor and the nature of the pathway.

4.1.6 Environmental risks associated with pollutant linkages at a site are assessed on the basis of

information obtained from the desk study, site observations and laboratory testing results

and are ranked into the following categories:

High: A pollutant linkage is present and this poses a significant risk to the identified receptors(s). Action must be taken to remove the pollutant linkage and/or reduce the risk.

Medium: A pollutant linkage is present and there is sufficient evidence to suggest that this is likely to pose a significant risk to the identified receptors(s). Further investigation and assessment should be undertaken to confirm this.




Low: A pollutant linkage is present and there is sufficient evidence to suggest that this is unlikely to pose a significant risk to the identified receptors(s). Further investigation and assessment may be undertaken to confirm this.

Very Low or Negligible: A pollutant linkage may be present but this poses no significant risk to the identified receptors(s).

4.2 Potential Sources of Contamination

4.2.1 The following potential on-site sources of ground contamination have been identified:

Potential contamination associated with the former Automatic Controls Factory, and more recently by the former Builders Merchants. Contaminants may include metals such as arsenic, PAH’s such as naphthalene, phenols, TPH’s and sulphates;

Potential contamination associated with fill materials used to form the existing raised, level site development platform. Contaminants may include metals, PAH’s, cyanides, phenols, sulphates, TPH’s and asbestos;

Potential historical leakage of fuel and machining oils from machinery and vehicles. Contaminants may include lead, TPH’s, BTEX and PAH’s; and

Potential generation of ground gases (methane and carbon dioxide) from the fill materials and Alluvium beneath the site.

4.2.2 The following potential off-site sources of ground contamination have been identified:

Potential cross-boundary migration of contamination associated with the former and existing commercial and light industrial premises on Holmbush Industrial Estate, which are in close proximity to, and up-gradient of, the site. Contaminants derived from off-site sources are likely to be similar to those derived from on-site sources.

4.2.3 The petrol filling station on the neighbouring Tesco site is in close proximity to the site,

however, it is approximately 3.0m lower than the site and adjacent to the stream. As such, it

is considered to be down hydraulic gradient of the site and therefore not considered to pose

a risk of cross-boundary migration of contamination to the site.

4.3 Potential Migration Pathways

4.3.1 The following potential migration pathways have been identified:

Inhalation

Breathing contaminated dust and/or hydrocarbon vapours from contaminated soils

and perched groundwater in outdoor or indoor air. Hydrocarbon vapours can be toxic

through inhalation.

Ingestion

Swallowing contaminated soils and/or dust either directly by deliberate consumption

or indirectly by eating, smoking or wiping mouths with dirty hands.




Dermal Contact

Touching contaminated soils and/or dust causes skin conditions. Contaminants, such

as heavy metals, can enter the human body by sorption through skin tissue and open

wounds.

Leaching

Infiltrating rainwater within contaminated Made Ground can leach soluble

contaminants into perched groundwater.

Migration of Contaminated Water

Contaminated perched groundwater can migrate laterally and/or vertically through

Made Ground and along preferential pathways, such as natural soil pores and fractures,

buried service corridors and man-made voids. This can eventually reach surface

watercourses.

Migration of Ground Gas/Vapours

Ground gases, such as methane and carbon dioxide, and/or hydrocarbon vapours can

migrate laterally and/or vertically through Made Ground and along preferential

pathways. These can accumulate within unprotected buildings and other structures,

leading to risks of explosion and asphyxiation in confined or unventilated spaces.

Aggressive Attack

Buried building materials can be damaged by direct contact with aggressive ground

conditions such as hydrocarbon attack on plastic drinking water supply pipes.

4.4 Potential Receptors of Contamination

4.4.1 The following potential human health and environmental receptors have been identified:

Future Site Users (e.g. customers and staff)

Construction and Maintenance Workers

Buried Concrete and Plastics (e.g. concrete foundations and water supply pipes)

Groundwater in the underlying Alluvium and Meadfoot Group, both of which are Secondary ‘A’ Aquifers

Surface water in the nearby stream

4.5 Pollutant Linkages and Environmental Risks

4.5.1 The potential Source-Pathway-Receptor relationships identified for the site bearing in mind the findings of the previous ground investigation and the proposed redevelopment of the site are summarised overleaf.




Table 4.1 Potential Source Pathway-Receptor Relationships

Source

Material/Activity

Potential

Contaminant Pathways Receptor Risk

Historical site uses,

Made Ground and

neighbouring site

uses

Metals, Cyanides,

Phenols, PAHs

Inhalation,

Ingestion, Dermal

contact

Construction and

Maintenance Workers High


Made Ground and

neighbouring site

uses

Metals, Cyanides,

Phenols, PAHs

Inhalation,

Ingestion, Dermal

contact

Future Site Users Medium

Made Ground Asbestos Containing

Materials Inhalation


Medium

Made Ground Leachable metals

and PAHs

Migration of mobile

contaminants in

permeable

strata

Groundwater in

underlying Secondary

‘A’ Aquifers

Low

Leaks and spills of

fuel and machining

oils, neighbouring

site uses

TPH, BTEX, PAHs

Inhalation,

Ingestion, Dermal

contact

Future Site Users and

Construction and

Maintenance Workers

Locally

High

(WS3)

Low

elsewhere

Leaks and spills of

fuel and machining

oils, neighbouring

site uses

TPH, BTEX, PAHs

Migration of mobile

contaminants in

permeable

strata

Groundwater in


‘A’ Aquifers and nearby

small stream

Low

Leaks and spills of

fuel and machining

oils, neighbouring

site uses

TPH, BTEX, PAHs Aggressive Attack Plastic Water Supply

Pipes Low

Made Ground and

Alluvium

Methane, Carbon

Dioxide, Carbon

Monoxide,

Hydrogen Sulphide

Migration through

permeable strata

and accumulation

inside buildings


Construction and

Maintenance Workers

Low

Made Ground and

Natural Strata

Water-soluble

Sulphate Aggressive Attack Buried Concrete Low




5 Japanese Knotweed Survey

5.1 Introduction

5.1.1 A visual, non-intrusive site walkover survey for Japanese knotweed was carried out at the site

by Craig Bulga, a qualified and experienced Ecologist, on 20th October 2015. The Japanese

Knotweed Survey required a systematic walkover of the entire site area and all adjacent

accessible areas to identify evidence of Japanese knotweed and hence confirm the findings of

the previous mapping by Aspect Ecology in 2010.

5.1.2 The survey was undertaken within the optimal period for Japanese knotweed identification

(i.e. between March and October) as the plants are actively growing and reproducing during

this period.

5.1.3 The survey should be regarded as representing only a snapshot in time and consideration

should be given to the requirement to update the information contained within this report if

there should be a delay of two years or more until the proposed site redevelopment works

take place.

5.2 Background

5.2.1 Japanese knotweed (Fallopia japonica) was introduced to the UK in the 19th century as an

ornamental plant. It is highly invasive, outcompetes native flora and fauna and has become

widespread in a range of environments, including derelict and overgrown sites, road and

railway verges and canal and riverbanks.

5.2.2 Japanese knotweed spreads through its crown, rhizome (underground stem / roots) and stem

segments, rather than from seeds. It can regenerate from fragments of rhizome from depths

of 2m below ground level and 7m laterally from a parent plant and can easily be spread

through the movement of infected soils.

5.2.3 Japanese knotweed is considered to be a constraint to development due to its rapid growth

and invasive nature. It can expose weaknesses in buildings, foundations, concrete and

asphalt. Japanese knotweed can grow 1m in a month and a 1cm fragment of rhizome can

produce a new plant in approximately ten days. In addition, rhizome segments can remain

dormant in soil for twenty years prior to producing new plants.

5.2.4 Japanese knotweed is listed in Schedule 9 Part II of the Wildlife and Countryside Act 1981 (as

amended). The Act states that it is an offence to "plant or otherwise cause to grow in the wild"

any plant listed in Schedule 9 Part II, and therefore care should be taken to avoid the spread

of this plant (such as during construction works).

5.2.5 Any soils infected with Japanese knotweed is classed as controlled waste under Part II of the

Environmental Protection Act 1990.




5.3 Methodology

5.3.1 The entire site area and all accessible areas within close proximity to the site boundaries were

inspected during the site walkover survey on 20th October 2015 by Craig Bulga.

5.3.2 The road verge of Daniels Lane along the south-western boundary and the parts of the

neighbouring Tesco site within close proximity to the south-eastern boundary were inspected

at close range. The external areas to the rear of the commercial / light industrial premises to

the north and east of the site were also inspected through the boundary fences. It was

however not possible to access a neighbouring soft landscaped area lying immediately

adjacent to the western corner of the site.

5.3.3 Any areas affected by Japanese knotweed were noted and an assessment made of its maturity.

Stands greater than 2cm in stem diameter were classified as mature stands and stands less

than 2cm stem diameter as juvenile stands.

5.4 Results

5.4.1 Japanese knotweed was NOT identified on any part of the site or within any adjacent accessible areas during the site walkover survey on 20th October 2015. This included the area of the gas governor station adjacent to the access point in the southern corner of the site where a small stand of Japanese knotweed had previously been mapped by Aspect Ecology as having been identified within this area in 2010. There was also no evidence of the other stands of Japanese knotweed that had been previously mapped at several locations across the neighbouring Tesco site.

5.5 Conclusion

5.5.1 The site is currently deemed to be free of Japanese knotweed and therefore no specialist management or remediation requirements relating to Japanese knotweed are considered to be necessary at this time.




6 Investigation Methodology

6.1 Objectives

6.1.1 The objective of this Geo-Environmental Investigation is to provide additional coverage and

testing across the site in order to complete updated environmental and geotechnical

assessments of the underlying ground conditions. This will then provide a robust data set to

assess potential contamination risks and liabilities associated with the ownership and

development of the site and recommend suitable foundation, floor slab, highway design

options for the proposed new Lidl development.

6.2 Clearance of Underground Services

6.2.1 Statutory service location plans for the site were provided by the Client prior to the intrusive

investigation. All exploratory hole locations were scanned by Opus using a cable avoidance

tool (CAT) as an additional precautionary measure prior to the advancement of each

exploratory hole.

6.3 Exploratory Holes

6.3.1 Six window sample holes (WS101-WS106) were advanced across the site using a small,

tracked, light percussion window sampling rig on 6th January 2016. Four of the window

sample holes (WS101-WS104) were positioned in a grid pattern across the former site

building footprint to target the previously inaccessible central part of the site, and hence

provide adequate site coverage. The remaining two window sample holes (WS105 and

WS106) were positioned in the former rear storage yard, close to the elevated TPH

concentration encountered in WS3 during the previous ground investigation, to determine

whether further TPH contamination was present. The window sample holes were advanced

to depths ranging between 1.80m and 4.00m below existing ground level (begl).

6.3.2 The approximate locations of the window sample holes are shown on the appended

Exploratory Hole Location Plan (Drawing No. J-B0950.00/G002-A).

6.3.3 Combined ground gas and groundwater monitoring wells were installed in WS101 (1.80m

deep), WS103 (3.00m deep) and WS106 (4.00m deep). The wells were constructed using

50mm HDPE plain pipe in a bentonite seal from existing ground level to 1.00m begl and

50mm HDPE slotted pipe in a gravel surround for the remaining depth of the window sample

holes. The wells were fitted with a gas tap assembly at ground level suitable for connection

to proprietary gas monitoring equipment and a lockable cover at ground level to provide

protection. WS102, WS104 and WS105 were backfilled with arisings.

6.4 Logging and Sampling

6.4.1 Engineers’ logs of the strata encountered in the window sample holes were developed in

accordance with BS EN ISO 14688 and copies are presented in Appendix ‘D’.




6.4.2 Standard Penetration Tests (SPT’s) were taken at regular 1.00m intervals in the window

sample holes to provide ‘N’ values for empirical assessment of strength and density

parameters of the strata.

6.4.3 Disturbed soil samples were taken at selected depths in the window sample holes, placed in

appropriate containers and submitted for chemical and geotechnical laboratory testing.

6.5 Chemical Testing

6.5.1 Selected soil samples were subjected to appropriate chemical testing at the MCERTS and

UKAS accredited laboratory of QTS Environmental for a suite of potential contaminants

taking account of the Preliminary Conceptual Site Model and site observations.

6.5.2 The following chemical testing was carried out on selected soil samples:

Standard Metals Suite 6 samples

Speciated Polycyclic Aromatic Hydrocarbons (PAH) 6 samples

Total Cyanide and Total Phenol 6 samples

Soil Organic Matter 6 samples

Asbestos Screen 6 samples

Speciated Total Petroleum Hydrocarbons (TPH) 6 samples

Benzene, Toluene, Ethyl benzene and Xylene (BTEX) 6 samples

6.5.3 The results of the chemical testing are presented in Appendix ‘E’.

6.6 Geotechnical Testing

6.6.1 Selected soil samples were subjected to appropriate geotechnical testing at the laboratories of Geolabs and QTS Environmental.

6.6.2 The following geotechnical testing of selected soil samples was carried out:

Moisture Content 5 samples

Plasticity Index 5 samples

pH 12 samples

Water-soluble Sulphate 12 samples 6.6.3 The results of the moisture content and plasticity index testing are presented in Appendix

‘F’. The results of the pH and water-soluble sulphate testing are included with the chemical

testing results presented in Appendix ‘E’.

6.7 Gas/Groundwater Monitoring

6.7.1 Combined ground gas and groundwater monitoring was undertaken in the three newly

installed monitoring wells (WS101, WS103 and WS105) and the two accessible previously

installed monitoring wells (BH3 and BH4) on one occasion on 13th January 2016.




6.7.2 Methane, carbon dioxide, oxygen, carbon monoxide and hydrogen sulphide concentrations

were measured using a calibrated Gas Data GFM436 Gas Analyser. Atmospheric pressure,

gas flow rates and groundwater levels were also recorded at the same time.

6.7.3 The results of the ground gas and groundwater monitoring are presented in Appendix ‘G’.




7 Investigation Results

7.1 Introduction

7.1.1 The ground conditions encountered in all six window sample holes advanced across the site

generally comprised hardstanding surfacing underlain by granular Made Ground to depths

ranging between 0.60m beneath the north-west of the site and 2.00m begl beneath the south-

east. Alluvium was locally present between 2.00m and 3.50m begl beneath the east of the

site and natural strata belonging to the Meadfoot Group was present beneath the Alluvium

and the remainder of the site to maximum proven depths ranging between 1.80m and 4.00m

begl.

7.2 Strata Observations

Made Ground

7.2.1 WS101-WS104 (located on the former site building footprint) penetrated a 160-200mm thick

concrete floor slab, which had steel reinforcement throughout and a plastic membrane at its

base, underlain by a 50-100mm thick granular sub-base of granitic sand.

7.2.2 WS105 and WS106 (located in the former rear storage yard) penetrated a 150mm thick

tarmacadam cap underlain by a 50-200mm thick granular sub-base of granitic gravel.

7.2.3 Two granular Made Ground horizons were encountered beneath the surface cover; an orange-

brown silty, sandy, cobbly gravel of siltstone to depths ranging between 0.30m and 0.65m

begl and an underlying medium brown-grey, variably mineral-stained black, blue, green and

orange, clayey, silty, sandy gravel of siltstone to depths ranging between 0.80m and 2.00m

begl. The deeper horizon was absent in WS101.

Natural Strata

7.2.4 WS106 encountered Alluvium, comprising a bed of loose, grey and brown, variably silty sand

from 2.00m to 2.70m begl underlain by a bed of soft, medium brown, very sandy silt from

2.70m to 3.50m begl.

7.2.5 The natural strata of the Meadfoot Group was encountered in WS101, WS102 and WS104 to

maximum proven depths of 1.80m, 2.00m and 3.00m begl respectively. This generally

consisted of a very weak, light brown-grey, foliated SILTSTONE, which was recovered from

the window sample holes as a very silty gravel.

7.2.6 In WS103, WS105 and WS106, a very weak, light pink-grey, foliated SILTSTONE, which was

recovered as a very clayey gravel, was encountered to the maximum proven depths of 3.00m,

3.00m and 4.00m begl respectively. This is believed to represent the weathered surface of

the Meadfoot Group.




7.3 Standard Penetration Tests (SPT’s)

7.3.1 The Standard Penetration Tests (SPT’s) taken at 1.00m intervals in the Made Ground and natural strata gave the following ranges of corrected ‘N’ values:

Table 6.1: Corrected SPT ‘N’ Values

Depth (m)

Exploratory Hole

WS101 WS102 WS103 WS104 WS105 WS106

1.00 27 13 15 28* 22* 17* 2.00 46 42 25 14 9 9 3.00 - - 46 46 4 7 4.00 - - - - 10 35

* SPT within Made Ground

7.3.2 WS101-WS104 refused on hard strata at depths of 1.80m, 2.00m, 3.00m and 3.00m begl

respectively. WS105 and WS106 were terminated at a depth of 4.00m begl.

7.4 Groundwater Observations

7.4.1 Groundwater strikes were observed in WS104 and WS106 at depths of 3.00m and 2.00m begl respectively during drilling.

7.4.2 During monitoring, a standing groundwater level of 3.60m begl was observed in the WS106

monitoring well. No standing groundwater levels were observed in the WS101 (1.80m deep) or WS103 (3.00m deep) monitoring wells.

7.5 Evidence of Potential Ground Contamination

7.5.1 No visual or olfactory evidence of ground contamination (i.e. staining or odour) was noted during the intrusive investigation. Variable black, blue, green and orange staining was noted in the granular Made Ground, however, this is considered to have represented mineral-staining rather than ground contamination.

7.6 Chemical Testing Results

7.6.1 The results of the chemical testing of soil samples have been reviewed in accordance with the current legislative framework and criteria to assess the risk to human health.

7.6.2 The soil sample chemical testing results have been compared to the Environment Agency Soil

Guideline Values (SGVs), DEFRA Category 4 Screening Levels (C4SLs), Opus In-House Tier 1 Screening Values (IHSVs) and Land Quality Management (LQM) Generic Assessment Criteria (GACs) 3rd Edition derived using CLEA 1.06 to be protective of human health.

7.6.3 The ‘Commercial’ site end use scenario has been adopted for the assessment of the site

bearing in mind the site redevelopment proposals. 7.6.4 The metal and PAH results for all tested Made Ground samples from both the previous

ground investigation (where available) and this Opus ground investigation have been subjected to a statistical Tier 1 Human Health Risk Assessment in accordance with the CL:AIRE and CIEH document titled ‘Guidance on Comparing Soil Contamination with a




Critical Concentration’ published in May 2008 using the ESI Contaminated Land Statistical Calculator software.

7.6.5 Under the land use planning system, the objective is to determine the ‘suitability for use’ of

the land under consideration and hence demonstrate that there is a 95% probability that the true population mean is below the set critical concentration, such as published SGVs, C4SLs and, in their absence, Opus Tier 1 IHSVs and LQM GACs for a ‘Commercial’ site end use.

7.6.6 Where the objective is to demonstrate ‘suitability for use’, the Null and Alternative

Hypotheses are as follows:

Null Hypothesis: “Is the true mean concentration more than or equal to that of the critical concentration?”

Alternative Hypothesis: “Is the true mean concentration less than the critical concentration?”

7.6.7 The Tier 1 Human Health Risk Assessment Spreadsheets are presented in Appendix ‘H’. 7.6.8 Soil Organic Matter (SOM) analysis has also been undertaken to enable the determination of

appropriate screening values for organic contaminants. The average SOM% value for the soils beneath the site is 0.5%, and therefore screening values applicable for 0.25% SOM have been used within the assessment.

Metals

7.6.9 Six Made Ground samples were analysed for a standard metals suite. Eight Made Ground

samples taken from the subject site were also analysed for metals as part of the previous

ground investigation.

7.6.10 One elevated arsenic concentration of 690mg/kg was detected in the WS6 0.60m sample during the previous ground investigation, which marginally exceeds the ‘Commercial’ C4SL for arsenic of 640mg/kg. Other notable arsenic concentrations (>100mg/kg) were detected in the WS102 0.50m, WS105 0.40m and WS3 1.7m samples.

7.6.11 The statistical analysis of the metals data set has confirmed that the Null Hypothesis has been

rejected for all metals including arsenic (i.e. the true mean concentration is less than the critical concentration).

Speciated PAH’s

7.6.12 Six Made Ground samples were analysed for speciated PAH’s. No Made Ground samples

taken from the subject site were analysed for speciated PAH’s as part of the previous ground

investigation.

7.6.13 No individual PAH concentrations exceed their applicable screening values in the six tested

samples, and none were detected above their laboratory detection limits. The statistical analysis of the PAH data set has confirmed that the Null Hypothesis has been rejected for all PAH’s (i.e. the true mean concentration is less than the critical concentration).

Total Cyanide and Total Phenol

7.6.14 Six Made Ground samples were analysed for total cyanide and total phenol. No Made Ground samples taken from the subject site were analysed for total cyanide and total phenol as part of the previous ground investigation.




7.6.15 No total cyanide or total phenol concentrations exceed their applicable screening values in

the six tested samples, and none were detected above their laboratory detection limits.

Asbestos Screen 7.6.16 Six Made Ground samples were screened for asbestos fibres. Six Made Ground samples taken

from the subject site were also screened for asbestos as part of the previous ground investigation.

7.6.17 No asbestos fibres were detected in the twelve screened samples.

Speciated TPH and BTEX 7.6.18 Six soil samples were analysed for speciated TPH and BTEX. No soil samples taken from the

subject site were analysed for speciated TPH and BTEX as part of the previous ground

investigation, however, fourteen soil samples were analysed for total C5-C35 TPH.

7.6.19 No individual TPH fractions or BTEX compounds exceeded their applicable screening values in the six tested samples, and none were detected above their laboratory detection limits. One potentially significant total C5-C35 TPH concentration of 3,300mg/kg was detected in the WS3 1.70m sample during the previous ground investigation. No detectable TPH concentrations were however recorded in soil samples taken at similar depths in nearby WS105 and WS106.

7.7 Geotechnical Testing Results

7.7.1 Six Made Ground samples and six natural strata samples were tested for pH and water-soluble sulphate. Eight Made Ground samples and six natural strata samples taken from the subject site were also tested for pH and/or water-soluble sulphate as part of the previous ground investigation.

7.7.2 The results of the pH and water-soluble sulphate testing are summarised as follows:

Made Ground

pH values between 4.9 and 8.0

Water-soluble sulphate values between 19mg/l and 223mg/l

Natural Strata

pH values between 5.6 and 7.9

Water-soluble sulphate values between 23mg/l and 73mg/l

7.7.3 Five natural strata samples were tested for moisture content and plasticity index. One sample represented the Alluvium and the other four samples represented the Meadfoot Group. No soil samples taken from the subject site were tested for moisture content or plasticity index as part of the previous ground investigation.

7.7.4 The results of the moisture content and plasticity index testing are summarised as follows:

Alluvium

Moisture content value of 34.3%

Non-plastic




Meadfoot Group

Moisture content values between 14.0% and 18.8%

Non-plastic

7.8 Ground Gas/Groundwater Monitoring Results

7.8.1 Gas monitoring results have been compared to guidance presented in CIRIA Report C665,

Assessing Risks Posed by Hazardous Ground Gases to Buildings, 2007.

7.8.2 CIRIA C665 indicates that ground gas protection measures may be necessary in new

buildings on sites where methane concentrations exceed a threshold value of 1% v/v and/or

where carbon dioxide concentrations exceed a threshold value of 5% v/v. The gas flow rate

is also considered in the required level of protection.

7.8.3 Maximum methane (CH4) and carbon dioxide (CO2) concentrations, as percentage volume

in air (%v/v), minimum oxygen (O2) concentrations (%v/v), maximum carbon monoxide

(CO) and hydrogen sulphide (H2S) concentrations, in parts per million (ppm), and gas flow

rates in litres per hour (l/hr) have been monitored on one occasion in the three newly

installed monitoring wells (WS101, WS103 and WS105) and the two accessible previously

installed monitoring wells (BH3 and BH4).

7.8.4 The results of the single gas monitoring visit are summarised as follows:

Methane was not recorded above the instrument detection limit (<0.1% v/v)

A peak carbon dioxide of 2.0% v/v was recorded in the monitoring wells

Carbon monoxide and hydrogen sulphide was not recorded above the instrument

detection limit (<1ppm)

Gas flow was not recorded in the monitoring wells.




B Assessment & Recommendations

8 Environmental Assessment

8.1 Soil

8.1.1 One elevated arsenic concentration of 690mg/kg was detected in the WS6 0.60m sample during the previous ground investigation, which marginally exceeds the ‘Commercial’ C4SL for arsenic of 640mg/kg. Other notable arsenic concentrations (>100mg/kg) were detected in the WS102 0.50m, WS105 0.40m and WS3 1.7m samples. All four of these samples were of the granular Made Ground which appears to include reworked natural strata. Naturally elevated arsenic concentrations are recorded as occurring in the Meadfoot Group strata. As such, it is considered likely that the elevated arsenic concentrations represent a natural, rather than man-made, source of ground contamination.

8.1.2 The statistical analysis of the metals data set has confirmed that the Null Hypothesis has been

rejected for arsenic (i.e. the true mean concentration is less than the critical concentration). 8.1.3 The current and any proposed future presence of hard cover (hardstanding surfaces and floor

slabs) will break the potential exposure pathways (inhalation, ingestion and dermal contact) between the Made Ground and site users, however, there is a potential human health risk to future construction workers from exposure during excavation and stockpiling of the Made Ground. On this basis, no remedial action is considered necessary for arsenic with respect to future site users, however, it is recommended that precautionary measures are adopted during the proposed site redevelopment works with respect to construction workers. These are discussed further in Section 8.4.

8.1.4 One potentially significant total C5-C35 TPH concentration of 3,300mg/kg was detected in

the WS3 1.70m sample during the previous ground investigation. No speciated TPH analysis was however undertaken on this sample and hence it is not known which TPH fractions are represented by this concentration. No visual or olfactory evidence of hydrocarbon contamination is reported as being noted in the WS3 1.70m sample. Furthermore, no evidence of hydrocarbon contamination was noted in WS105 and WS106, purposefully located within close proximity to WS3, as part of the recent Opus ground investigation and no detectable TPH concentrations were recorded in soil samples taken at similar depths in these two exploratory holes. On this basis, the single elevated TPH concentration does not seem to represent a wider issue and therefore no remedial action is considered necessary for TPH with respect to both human health and ‘controlled waters’.

8.1.5 The water-soluble sulphate concentrations in the tested Made Ground and natural deposits

samples indicate that the risk posed to future buried concrete structures is negligible. This topic is characterised further in Section 9.6 of this report.




8.2 Ground Gas

8.2.1 The results of the single gas monitoring visit carried out at the site on 13th January 2016

recorded no methane concentrations above the instrument detection limit (<0.1% v/v), a

peak carbon dioxide concentration of 2.0% v/v and no gas flow.

8.2.2 Based solely on the results of the recent gas monitoring visit, the Gas Screening Value (GSV)

classifies the site as ‘Characteristic Situation 1’ in accordance with CIRIA Report C665

whereby no methane / carbon dioxide protection measures are required in proposed new

commercial developments. Despite this however, the site is in a higher probability area

where between 10% and 30% of homes are above the radon action level and where full radon

protective measures are necessary in the construction of new buildings or extensions.

Although BR211: 2015 relates specifically to residential properties, an employer has a duty of

care to protect its employees from exposure to significant levels of radon, and maintain radon

levels of less than 400 becquerels within commercial properties.

8.2.3 The provision of full radon protection measures in the construction of the new food store will

address any potential risk to future site users from methane and/or carbon dioxide. The

above classification of the site and/or the extent of gas monitoring undertaken to date are

subject to agreement with the Local Authority Environmental Health Officer (EHO).

8.3 Revised Conceptual Site Model

8.3.1 The final Conceptual Site Model based on information obtained from the intrusive investigation, the Tier 1 Human Health Risk Assessment and the Ground Gas Risk Assessment has identified that the following potential pollutant linkages remain at the site and may require consideration at the detailed design and construction stages.

Table 8.1 Revised Pollutant Linkages and Environmental Risks

Source

Material/Activity

Potential


Made Ground Arsenic

Inhalation,

Ingestion, Dermal

contact

Construction Workers High


Made Ground and

neighbouring site

uses

Other Metals,

Cyanides, Phenols,

PAHs

Inhalation,

Ingestion, Dermal

contact


Construction and

Maintenance Workers

Very Low

Made Ground Asbestos Containing

Materials Inhalation


Very low

Made Ground Leachable metals

and PAHs

Migration of mobile

contaminants in

permeable

strata

Groundwater in


‘A’ Aquifers

Very low

Leaks and spills of

fuel and machining

oils, neighbouring

site uses

TPH, BTEX, PAHs

Inhalation,

Ingestion, Dermal

contact


Construction and

Maintenance Workers

Locally

Low (WS3)

Very low

elsewhere




Source

Material/Activity

Potential


Leaks and spills of

fuel and machining

oils, neighbouring

site uses

TPH, BTEX, PAHs

Migration of mobile

contaminants in

permeable

strata

Groundwater in


‘A’ Aquifers and nearby

small stream

Very low

Leaks and spills of

fuel and machining

oils, neighbouring

site uses

TPH, BTEX, PAHs Aggressive Attack Plastic Water Supply

Pipes Very low

Made Ground and

Alluvium

Methane, Carbon

Dioxide, Carbon

Monoxide,

Hydrogen Sulphide

Migration through

permeable strata

and accumulation

inside buildings


Construction and

Maintenance Workers

Very low

Made Ground and

Natural Strata

Water-soluble

Sulphate Aggressive Attack Buried Concrete Very low

8.4 Health & Safety

8.4.1 The Principal Contractor should provide an assessment of the appropriate procedures

required to protect site workers from the materials likely to be encountered at the site.

8.4.2 The following basic health and safety measures should be adopted as a minimum during the

site redevelopment works:

Basic Personal Protective Equipment (PPE) including hard hats, gloves, coveralls and steel toe-capped boots to be worn at all times;

Eating, drinking and smoking to be forbidden at all times except in designated mess areas;

Breathing equipment to be available for those working in confined or unventilated spaces; and

Workers should be mindful of the likelihood of elevated arsenic concentrations being present whilst disturbing, excavating or stockpiling Made Ground and/or natural strata.

8.4.3 If ground conditions should differ significantly from those encountered during the intrusive

investigation, including the discovery of any visible or odourous contamination, site

redevelopment works should be suspended until the suspect material has been inspected and

assessed by a competent Geo-Environmental Engineer.

8.5 Waste Disposal

8.5.1 The reuse of Made Ground as engineered fill should be undertaken in accordance with an appropriate Environment Agency licence as defined in the statutory guidance on the ‘Definition of Waste’ or CL:AIRE Code of Practice.

8.5.2 Any materials designated for off-site disposal are likely to require classification by the Waste

Acceptance Criteria (WAC) in accordance with the Landfill Regulations. No WAC testing has been undertaken as part of this investigation.




8.6 Liaison with Regulators

8.6.1 It is recommended that this report be submitted to the Local Authority Environmental Health

Officer for review and comment prior to any irrevocable action taking place.

8.7 Water Supply Pipes

8.7.1 No protection is anticipated for future water supply pipes, however it is recommended that this report be submitted to the relevant Water Supply Authority to confirm the necessary level of protection, if any, for future plastic water supply pipes.

8.8 Environmental Protection

8.8.1 The following environmental protection measures should be adopted as a minimum during the site redevelopment works:

Covering or dampening of spoil to prevent the spread of dust;

Containment of surface water runoff to prevent the pollution of surface water drains, sewers etc.; and

Cleaning and washing of boots, vehicle wheels and other equipment at site entry and exit points to prevent the spread of mud.




9 Geotechnical Assessment

9.1 Discussion

9.1.1 The Made Ground across the site generally comprised hardstanding surfacing underlain by

granular Made Ground to depths ranging between 0.60m beneath the north and west of the

site and 2.00m begl beneath the south and east. The granular Made Ground was essentially

an orange-brown silty, sandy, cobbly gravel of siltstone underlain by a medium brown-grey,

clayey, silty, sandy gravel of siltstone.

9.1.2 Made Ground beneath the building footprint of the proposed new Lidl food store in the north

of the site, represented by BH3, WS5, WS101 and WS103, extended to depths ranging

between 0.30m and 1.00m begl. Deeper Made Ground, represented by WS3, WS6, WS105

and WS106, extended to depths ranging between 1.60m and 2.60m immediately to the south-

east of the proposed footprint.

9.1.3 Beneath the proposed footprint, natural strata belonging to the Meadfoot Group was

encountered directly underlying the Made Ground in BH3, WS5, WS101 and WS103. This

essentially comprised an approximately 1.00-2.00m thick layer of very weak, light pink-grey,

foliated SILTSTONE (believed to represent the weathered surface of the Meadfoot Group) to

depths between approximately 1.30m and 3.00m begl underlain by a very weak, light brown-

grey, foliated SILTSTONE to the maximum proven depth of 4.00m begl.

9.1.4 Alluvium, essentially comprising loose, grey and brown, variably silty sand and sandy silt,

was not encountered beneath the proposed footprint but was locally present in WS3 and

WS106 at depths between 2.00m and 3.50m begl to the south-east of the proposed footprint.

9.1.5 The Standard Penetration Tests (SPT’s) taken at 1.00m intervals within the exploratory holes

beneath the building footprint of the proposed new Lidl food store in the north of the site

gave the following ranges of corrected ‘N’ values:

Table 9.1: Corrected SPT ‘N’ Values beneath Proposed Footprint

Depth (m)

Exploratory Hole

BH3 WS5 WS101 WS103

1.00 22 27 27 15 2.00 >50 33 46 25 3.00 48 43 - 46 3.50 >50 - - -

9.1.6 BH3, WS5, WS101 and WS103 refused on hard strata at depths of 3.50m, 3.00m, 1.80m and

3.00m begl respectively.




9.1.7 The Standard Penetration Tests (SPT’s) taken at 1.00m intervals within the exploratory holes

immediately to the south-east of the building footprint of the proposed new Lidl food store

gave the following ranges of corrected ‘N’ values:

Table 9.2: Corrected SPT ‘N’ Values in other areas

Depth (m)

Exploratory Hole

WS3 WS6 WS105 WS106

1.00 23* 16* 22* 17* 2.00 10** 5* 9 9** 3.00 19 33 4 7** 3.50 - 50 - - 4.00 28 - 10 35 5.00 32 - - - 6.00 50 - - -

* SPT within Made Ground

** SPT within Alluvium

9.1.8 WS3 and WS6 refused on hard strata at depths of 6.000m and 3.50m begl respectively.

WS105 and WS106 were terminated at a depth of 4.00m begl. 9.1.9 Groundwater strikes were observed at depths of 2.20m and 2.00m begl in WS3 and WS106

during drilling. No groundwater strikes were observed in the other exploratory holes within the vicinity of the proposed footprint. During monitoring, a standing groundwater level of 3.60m begl was observed in the WS106 monitoring well.

9.2 Foundation Design

9.2.1 At present the finished ground levels and anticipated loadings for the proposed Lidl retail store are not known, although it is assumed the finished level will be similar to existing. The following account should therefore be reviewed on completion of the detailed design and planning process.

9.2.2 Taking account of the soil descriptions and SPT results across the site, particularly those

within the proposed building footprint of the new Lidl food store, the natural weathered strata of the Meadfoot Group are anticipated to represent a suitable founding horizon for the new Lidl retail store, and it is recommended that traditional strip and/or pad foundations will represent a suitable founding solution for the proposed store. A minimum foundation depth in the region of 1.50m begl will be required to achieve full penetration of the Made Ground and any other potentially reworked natural materials. Care should be taken in the south-eastern area of the proposed building footprint where Made Ground and alluvial materials may be encountered to deeper depths, which will need to be fully penetrated by any foundations.

9.2.3 For guidance purposes, for a 0.60m wide strip and up to 2.00m square pad foundation, cast

at the minimum depth of 1.50m onto the weathered Meadfoot Group, a net allowable bearing pressure in excess of 200kN/m2 may be adopted for initial design purposes, restricting total settlements to a maximum of 25mm. Higher allowable bearing pressures will be available with increasing founding depth.




9.2.4 In accordance with EC7, these values must be checked against the actual proposed factored foundation design loads, and a settlement calculation undertaken. At this stage, the foundation loadings are not known and hence the foundation widths and depths cannot be confirmed until this information is available.

9.2.5 Alternatively, given the limited recorded thickness of Made Ground beneath the proposed

building footprint, consideration could also be given to the adoption of a raft foundation, with the removal, sorting, enhancement and compaction of a suitable layer of granular material beneath the building.

9.2.6 The potential influence of trees is not considered to be of concern for the new Lidl food store

as there are no existing or proposed trees within influencing distance.

9.3 Floor Slab Design

9.3.1 Assuming that strip and/or pad foundations are adopted for the foundation design and in view of the relatively thin layer of Made Ground beneath the proposed building footprint, it is anticipated that a ground bearing floor slab could be adopted as less than 600mm of Made Ground would be anticipated beneath the slab construction. If deeper Made Ground is present, this will require the excavation of the existing near-surface soils and replacement with a suitably engineered granular layer. Alternatively, a suspended floor may be adopted.

9.3.2 The floor slab design will need to include the provision of full radon protection measures

which should be confirmed through consultation with the EHO. This topic is discussed further in Section 8.2.

9.4 Pavement Design

9.4.1 The existing near-surface soils should provide a preliminary Design CBR value of 2%,

however, given their predominantly granular nature, this should be increased significantly by

heavy proof rolling. It is anticipated that, following proof rolling, a CBR value in excess of

10% should be available on the Made Ground materials. These values should be confirmed

by in-situ testing when the anticipated formation level is known.

9.5 Construction

9.5.1 Anticipated excavation depths should be readily achieved using conventional plant (JCB 3CX

or similar) within the Made Ground and natural strata.

9.5.2 Support must be provided for all excavations requiring entry by site workers in accordance with guidance presented in CIRIA Report 97 ‘Trenching Practice’.

9.5.3 Groundwater may be locally encountered in any excavations at depths in excess of 2.00m

begl and localised dewatering of excavations may be required. Although dependent on the rate of groundwater entries, traditional sump and pumping techniques may suffice.

9.6 Concrete Specification

9.6.1 The ground conditions, pH values and water-soluble sulphate concentrations have been

assessed for potential aggressive attack on concrete in accordance with BRE Special Digest 1

‘Concrete in Aggressive Ground (2005)’.




9.6.2 The results indicate that the Made Ground and natural strata beneath the site fall within

Design Sulphate Class DS-1 and ACEC (Aggressive Chemical Environment for Concrete)

Class AC-1.

9.6.3 The specific concrete mixes for the DS Class to be used at the site will be determined, mindful

of the ACEC Class, by the site-specific concrete requirements in terms of the required

durability and structural performance. These are assessed in terms of the Structural

Performance Level (SPL) and any Additional Protection Measures (APM).

9.7 Soakaways

9.7.1 Soakaway tests in accordance with BRE 365 have not been undertaken as part of this investigation. The use of soakaways for surface water drainage for the proposed site redevelopment may be feasible given the presence of relatively thin Made Ground and the granular nature of the weathered top of the Meadfoot Group, however, the exploratory holes reached refusal at shallow depth and hence a relatively impermeable bedrock layer may restrict their potential. In addition, the site is at an elevated level in comparison to the neighbouring Tesco site to the south-east, and is retained by a wall of concrete block construction running along its south-eastern site boundary, and hence there is the potential for shallow infiltration systems to have a detrimental effect on the retaining wall and neighbouring property. If soakaways are to be considered, formal testing will be required in accordance with BRE365.

9.8 Retaining Wall

9.8.1 It is understood that the existing retaining wall running along the south-eastern site boundary will be removed and replaced with a graded, landscaped bank as part of the site proposals. If these site proposals should be amended and the retaining wall should be maintained, a structural survey of the wall will be necessary.




10 Recommendations

10.1 The following further works are recommended prior to the redevelopment of the site:

Submission of this report to the Local Authority Environmental Health Officer for review and comment prior to any irrevocable action taking place. This should include there requirements in respect of the current ground gas assessment. Submission of this report to the relevant Water Supply Authority to confirm the necessary level of protection, if any, for future plastic water supply pipes. Confirmation of design CBR values for external areas. Formal soakaway testing in accordance with BRE365 if required.

Registered in England & Wales,

Company Reg. No: 2847568

Reg Office: Willow House, Brotherswood Court

Great Park Road, Bristol, BS32 4QW

Opus International Consultants (UK) Ltd S3, 3800 Parkside, Birmingham Business Park Birmingham, B37 7YG United Kingdom t: +44 121 329 1560 f: +44 121 788 0757 w: www.opusinternational.co.uk

lidl uk gmbh geo-environmental investigation report · lidl development and an existing small area...

Documents