R-STG1772N-PRS01-Rev 01 (Excl App D).pdf

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Residential developmentFinedon Road, Irthlingborough

Proposed residential development

off

Finedon Road

Irthlingborough

Northamptonshire

REMEDIAL STRATEGY

Soiltechnics Ltd. Cedar Barn, White Lodge, Walgrave, Northampton. NN6 9PY.

Tel: (01604) 781877 Fax: (01604) 781007 E-mail: [email protected]

Report originators

Prepared by

Sam Dean B.Sc,(Hons)

[email protected]

Geo-environmental Engineer, Soiltechnics Limited

Supervised

David Dunkley B.Sc, (Hons)., CEnv, MSEE,

FGS

[email protected]

Senior geo-environmental Engineer, Soiltechnics Limited

Reviewed

Stephen Cragg B.Sc (Hons)., F.G.S.

[email protected]

Director, Soiltechnics Limited




Report status and format

Report statusReport

section

Principal coverage

Revision Comments

1 Introduction 01 Updated November 2010

2 Description of the site 01 Updated November 2010

3 Site history 01 Updated November 2010

4 Geology of the area 01 Updated November 2010 5 Geohydrology of the area 01 Updated November 2010

6 Summary of previous investigations 01 Updated November 2010

7 Preliminary remedial measures 01 Updated November 2010

8 Discussion with Environment Agency and Environmental

Health Officer

01 Updated November 2010

9 Final remedial strategy 01 Updated November 2010

List of drawings

StatusDrawing Principal coverage

Revision Comments

Drawing PRS01 Site location plan 0

Drawing PRS02 Plan showing existing site features and location of

exploratory points


Drawing PRS03 Plan showing site development proposals and location

of exploratory points


Drawing PRS04 Plan showing existing site features, location of

exploratory points and proposed cut and fill contours



exploratory points and surface geology following site

strip



exploratory points and phases of cut and fill operations



exploratory points and location of approximate

volumes of hydrocarbon impacted soils requiring

remediation



exploratory points and plots in which capping layers

0 Included November 2010




List of appendicesAppendix Content

A Definitions of geo-environmental terms used in this report.

B Report by GRS

CMethod Statement in relation to decommissioning of above ground tank and removal of hydrocarbon

impacted soils (R-STG1772N-MS01-Rev0)

D Groundwater Risk Assessment

EMethod statement in relation to excavation and treatment of hydrocarbon impacted soils (R-

STG1772N-MS02-Rev01)

F Remedial Target Worksheets




1.0 Introduction

1.1 This remedial strategy describes recommendations to render the site fit for purpose in

relation to chemical contamination identified during past and recent intrusive

investigations. It supersedes our previous Preliminary Remedial Strategy report ref R-

STG1772N-PRS01-Rev0.

1.2 We understand the development will comprise the construction of two to three storey

houses together with access roads and garden/landscaped areas. We have receivedlayout drawings of the proposed development with the layout presented on Drawing

PRS03.

1.3 It should be noted that the some of the following information has been extracted from

Envirocheck data presented in a previous report for the site undertaken by Nicholls

Colton Environmental (ref G08013) dated May 2008. Considering the time since this

report was issued, some the data may have been superseded.

2.0 Description of the site

2.1 The site is located to the north-west of Irthlingborough town centre and situated

between the B5348 and the A6. The grid reference for the site is 494150, 271290. A

plan showing the location of the site is presented on Drawing PRS01.

2.2 At the time of our investigations, the site was accessed from Finedon Road via adriveway surfaced in bituminous bound material and located between some residential

properties. The driveway leads in to a parking area surfaced in bituminous bound

material located immediately adjacent to the entrance to the main building on site. The

main building is of masonry construction with a number of single storey external

workshops and storage areas constructed from profiled sheeting and timber. Gravel

and concrete/bituminous bound hardstanding surrounds the main building.

2.3 Unsurfaced areas of open space were present to the north and west of the mainbuilding, beyond which an embankment feature was evident, ranging from 1.5m to

3.0m in height. A field laid to rough grass occupied the eastern part of the site which

sloped to the north by approximately 1 in 14 towards a small stream flowing east-west

across the site. The stream was dry at the time of our investigations, and it is

understood that the stream runs dry for a large amount of the year. Site levels rise




2.4 An above ground tank was located to the south-western corner of the main building on

site, with an approximate 5300 litre capacity. It is understood from previous

investigations undertaken by Nicholls Colton that an area to the north of the main

building was used as a sump for the disposal of waste oil when the site was utilised as a

coach works. Furthermore, Nicholls Colton also identified pipe work likely to be

associated with a cess pit located to the north-eastern corner of the site. A plan

showing the observed site features and location of exploratory points is presented on

Drawing PRS02.

2.5 The nearest surface water feature is the stream located in northern parts of the site.

The River Nene is located approximately 1km to the south-east of the site. Tributaries

of the River Nene are recorded 250mand 750m to the south-east of the site.

3.0 Site history

3.1 The 1885 map records the site as open space with a small quarry and lime kiln situated

to the centre of the site, which by 1900 has been extended with a further lime kilnrecorded. Small buildings are recorded on site also.

3.2 The 1926 map indicates the presence of a large building to the south of the site, with

the quarry and lime kilns to the centre of the site now recorded as a pond and spoil

heap.

3.3 The 1958 map indicates the presence of a small building adjacent to the stream in the

centre of the site.

3.4 The 1964 map indicates construction of further buildings and extension of the large

building to the south of the site. Buildings are now recorded as a works with some

embankment features present to the centre of the site.

3.5 The 1976 map records two above ground tanks on site, one recorded on the south-

western of the main building (now recorded as a depot) and the other recorded to thecentre of the site.

3.6 The 1993 map records the main large building on the site as a factory in addition to

further extensions. The building to the north of the site is no longer present.




5.0 Geohydrology of the area

5.1 Inspection of the aquifer designation map records the majority of the site as a major

aquifer, reflecting the near surface Great Oolite Limestone deposits. The soils

containing the aquifer are recorded as high leaching potential. The area of Upper

Estuarine deposits recorded to the north of the site in the area of the stream are

recorded as a minor aquifer of high leaching potential, with a small area on the western

boundary of the site recorded as a major aquifer of intermediate leaching potential.

5.1 The closest registered groundwater abstraction is recorded 1365m to the east of the

site used for irrigation purposes. The site is not located within a zone protecting a

potable water supply abstracting from a major aquifer (i.e. a source protection zone).

The site is not recorded in a fluvial or tidal flood plain.

6.0 Summary of previous investigations

6.1 Nicholls Colton

6.1.1 Investigations have previously been undertaken by Nicholls Colton Geotechnical in May

2008 (report ref G08013) with supplementary investigations undertaken in March 2009

(report ref GR0813-2).

6.1.2 In summary the following was identified from the initial phase of investigations:

• Visual and olfactory evidence of hydrocarbon contamination identified within

backfilled former quarry to the centre of the site and adjacent to the above

ground fuel tank on the south-western corner of the building.

• Elevated concentrations of meals including arsenic, cadmium, lead, nickel,

copper and zinc identified within near surface Made Ground deposits following

laboratory testing.

• Elevated concentrations of organic contaminants including benzo(a)pyrene and

dibenzo(a,h)anthracene identified within Made Ground soils at the sitefollowing laboratory testing.

• Elevated concentrations of total petroleum hydrocarbons (TPH) identified in

near surface Made Ground soils adjacent to the above ground fuel tank

described above and at depth within the area of the former quarry following

laboratory testing.




6.1.3 Further investigations were proposed following completion of the initial phase of works,

as follows;

• Rotary boreholes to access potential impact of contamination identified on the

underlying aquifer

• Installation of standpipes within the rotary boreholes will be required to allow

sampling and testing of groundwater and a possible groundwater risk

assessment.

• Supervision/a watching brief of the demolition of existing factory will berequired.

• It should be anticipated that further hotspots of contamination (particularly

hydrocarbons) may be located and need to be sampled and potentially

removed.

• A Site Waste Management Plan should be produced prior to development of

the site.

• A groundwater risk assessment may be required to assess the impact of the site

on the stream.• Water sampling of the stream should be undertaken at both the inlet and the

outlet to the site to ascertain whether the site is impacting upon the quality of

the stream water at present.

• The Environment Agency should be approached to obtain a Waste Management

Exemption with respect to the proposed earthworks exercise.

6.1.4 The findings of the supplementary investigations led to the following measures to be

recommended:

• Further investigation and probable removal (or treatment) of the hydrocarbon

impacted soils in the area of WS2.

• Removal/treatment of hydrocarbon impacted soils in the area of the small

backfilled quarry (area around WS10). A groundwater risk assessment should

be undertaken to determine appropriate remediation target values.

• Installation of a 600mm thick clean soil cover layer in areas of the site wheremade ground is present. This will include the existing Brownfield Zone and

areas of the site to which Made Ground soils will be moved as part of the

proposed cut/fill operation (i.e. parts of the Greenfield Zone).

• Supervision/a watching brief of the demolition of the existing factory and of the

earthworks exercise. It should be anticipated that further hotspots of




6.2 Soiltechnics Limited

6.2.1 Soiltechnics Limited were instructed to undertake intrusive investigations at the site in

July 2010 to assess the present day extent contamination of previously identified. In

addition, further cable and tool percussive boreholes and rotary boreholes were

positioned around the site in order to obtain geotechnical information for

foundation/pavement design and to install groundwater monitoring standpipes to

assess potential contamination in the underlying major aquifer.

6.2.2 A total of four cable and tool percussive boreholes, seven rotary boreholes, four insitu

CBR tests and eleven trial pits were undertaken at the site. Positions of trial pits and

boreholes for foundation design purposes were positioned by Brookbanks Limited. Trial

pit and borehole locations to investigate the present day extent of contamination were

positioned by Soiltechnics Limited and agreed with the Environmental Health Officer

(EHO) at East Northants District Council. Refer to Drawing PRS02 for locations of

exploratory points.

6.2.3 Investigations into the extent of contamination previously identified in the former

quarry to the centre of site indicated that hydrocarbons had generally not migrated any

further than that outlined by Nicholls Colton. A small amount of hydrocarbon

contamination was observed in trial pit TP11 between depths of 1.25m to 1.6m below

surface level which was not previously identified. Trial pit TP04 confirmed the presence

of hydrocarbon contamination between depths of 0.9m to the base of the Made

Ground fill at 4.0m. No contamination was observed during the drilling of boreholes

BH01-BH04 and RBH01-RBH06 and all other trial pits but hydrocarbon odours werenoted by the drilling operatives at depths between approximately 7.0m to 7.5m within

deposits of limestone in borehole RBH07.

6.2.4 Laboratory testing of a number of soil samples for within the former quarry area at the

site indicate that total petroleum hydrocarbon contamination is prevalent in soils in

TP04 to depths of at least 2.5m below surface level (refer to attached comparison of

laboratory data). Concentrations pose a risk to human health at present.

Concentrations have been recorded in trial pit TP11 at a depth of 1.4m, however, do not

exceed relevant GAC (generic assessment criteria) in relation to human health and

residential end use.

6.2.5 Concentrations of hydrocarbons identified in the quarry area during previous

investigations by Nicholls Colton indicate that soils between depths of 1 0m and 5 4m




6.2.7 Concentrations of contaminants measured within groundwater by Nicholls Colton

indicate minor concentrations of arsenic, copper and mercury. Test data undertaken by

Soiltechnics indicates that elevated concentrations of TPH and benzo(a)pyrene exist in

groundwater within the area of borehole R5. Further testing is being undertaken on

water samples from the site.

6.2.8 During subsequent water monitoring visits to the site, free phase hydrocarbon was

observed on top of the water column in borehole R5. Oil was recorded with an

interface meter to be approximately 400mm thick in early August 2010. During furthermonitoring visits water and free phase liquid was purged from the borehole by hand

and by mechanical pumping (refer to Appendix B for GRS report). Measurements

indicated that free phase initially pumped from the borehole was not recharging.

Recent monitoring visits have not recorded the presence of free phase within borehole

R5, with sampling indicating a minor residue of free phase and associated hydrocarbon

odour.

7.0 Preliminary remedial measures

7.1 Based on the reports presented by Nichols Colton and subsequent fieldwork, the

following remedial measures were recommended within our preliminary remedial

strategy (ref R-STG1772N-PRS01-Rev0);

1. Installation of full radon protection measures in all new developments

2. Following demolition of existing buildings inspection of exposed soils should be

undertaken to confirm, or otherwise, the presence of further contamination

3. Installation of a capping layer in areas of Made Ground

4. Removal and treatment of hydrocarbon impacted soils in area of historic quarry

5. Decommissioning of the existing above ground fuel tank and associated

hydrocarbon impacted soils

6. Potential treatment of hydrocarbon impacted groundwater

7. Continued monitoring of groundwater quality following remedial works

8. Validation of excavations following removal of hydrocarbon impacted soils

9. Potential groundwater risk assessment

8.0 Discussion with Environment Agency and Environmental Health

Officer




8.2 On review of laboratory testing undertaken to date, and taken into consideration

environmental and geological/hydrological factors at the site, a Groundwater Risk

Assessment (GRA) was completed to identify the potential risk to water receptors. The

compliance point for the GRA was recommended by the Environment Agency to be

200m from source zone at the site. This was based on the contaminated part of the site

being located in the minor aquifer of the Upper Estuarine Series and the nearest water

receptor of significance being a spring located approximately 200m to the east of the

site.

8.3 Following completion of the GRA, if a potential risk was highlighted, remediation of

hydrocarbon impacted soils would be undertaken. It was agreed that soils would be

excavated and ex-situ remediation using windrows positioned in an appropriate area of

the site would be undertaken. The location of soils placed in the windrows relative to

their position from the excavation should be recorded, with the number and frequency

of validation samples agreed with the Environment Agency and ENC.

8.4 If hydrocarbon impacted soils were to be remediated on site then a Mobile TreatmentLicence (MTL) would be required to undertake such works.

8.5 Following site cut and fill operations, areas in which Made Ground deposits remain at

crop will require a capping layer as agreed with ENC. It was agreed that where natural

soils are anticipated to remain at crop validation would be undertaken and confirmed

(or otherwise) on a ‘plot-by-plot’ basis. Similarly, areas where capping layers are

introduced will be validated, with thicknesses confirmed on completion.

8.6 On completion of all remedial works, further groundwater monitoring wells were

agreed to be installed at the site to validate whether hydrocarbon concentrations

identified in groundwater prior to remedial works have reduced to an acceptable level

post remedial works. Remedial target concentrations will be calculated using the

Environment Agency Remedial Targets Spreadsheet.




9.0 Final remedial strategy9.1 Introduction

9.1.1 Based on the reports presented by Nichols Colton and subsequent fieldwork, in addition

to discussions undertaken with relevant authorities, the following remedial measures

were agreed to be undertaken at the site.

1. Installation of full radon protection measures in all new developments2. Installation of hydrocarbon vapour resistant membranes in properties

constructed in areas impacted by hydrocarbon contaminated soils

3. Following demolition of existing buildings inspection of exposed soils should be

undertaken to confirm, or otherwise, the potential presence of further hotspots

of contamination

4. Installation of a capping layer in areas where Made Ground deposits exist at

crop following site works

5. Decommissioning of the existing above ground fuel tank and associatedhydrocarbon impacted soils

6. Groundwater Risk Assessment (GRA) undertaken to determine potential impact

of hydrocarbon contaminated soils and groundwater on local water receptors

7. Removal and treatment of hydrocarbon impacted soils in the area of the

historic quarry if required following completion of the GRA. Following

excavation monitoring and compliance testing should be undertaken.

8. Treatment of hydrocarbon impacted groundwater if required

9. Validation of any excavation following removal of hydrocarbon impacted soils

10. Continued monitoring of groundwater quality following remedial works

9.1.2 The remedial strategy outlined above is discussed in more detail in the following

sections.

9.2 Installation of radon and hydrocarbon resistant membranes

9.2.1 The site is located within an area where full radon protection is recommended, based

on data provided by Building Research Establishment (BRE) and the British Geological

Survey.

9.2.2 As a precaution, it is recommended that hydrocarbon resistant membranes are installed




9.3 Identification and procedure to remediate contaminative hotspots

9.3.1 Following demolition of the existing buildings on site, further contamination may be

encountered in soils in areas which have not previously been investigated. In the event

of such areas being identified by contractors on site, Soiltechnics Limited will be notified

of the impacted area and a suitably qualified geo-environmental engineer will visit site

to assess the hotspot.

9.3.2

If required, contaminated soils will be excavated using mechanical plant provided by theon site contractors. Following removal of soils, the engineer will confirm whether or

not all of the impacted soils have been removed by visual and olfactory methods.

9.3.3 Representative soil samples will be taken from the excavation to validate that all

contaminated soils have been successfully removed and that remaining soils do not

present a risk of causing harm to human health/water receptors. Samples will be taken

and sent for testing to an independent specialist testing house, which operates a quality

assurance scheme.

9.3.4 Where previously unidentified contamination is noted, it will be recorded and the

results from any validation testing will be presented along with location drawings to the

EA and ENC.

9.4 Capping layer

9.4.1 With reference to Drawings PRS04 to PRS06 which indicate the locations and phases of proposed cut and fill operations at the site, following the site strip, areas of naturally

deposited Great Oolite Limestone are anticipated to remain at crop in central and

eastern parts of the site. Capping material will not be required in gardens and

landscaped areas in these locations where natural soils remain at crop. Areas of the site

within which Made Ground deposits are used as engineered fill or where such deposits

remain at crop following the site strip will require a capping layer in garden/landscaped

areas. Drawing PRS08 indicates the individual plots in which a capping layer is

anticipated to be required.

9.4.2 The capping layer should be a minimum of 600mm thick in any productive garden areas,

and areas likely to be accessible to young children (considered the critical human

receptor) on a regular (daily basis). In our opinion, this may be reduced to 300mm in

landscaped areas although this should be agreed with the Local Authority Capping




9.5 Decommissioning of the existing above ground fuel tank

9.5.1 A separate method statement has been prepared regarding the decommissioning of the

existing above ground fuel tank and associated hydrocarbon impacted soils (ref R-

STG1772N-MS01-rev0) which is presented in Appendix C.

9.6 Groundwater Risk Assessment (GRA)

9.6.1 Following discussion with the EA and ENC, the contamination identified within the

backfilled former quarry was identified as posing a potential risk to groundwater

therefore a GRA was agreed to be undertaken.

9.6.2 The assessment of the hydrocarbon impacted soils in the former quarry suggests that

those contaminated soils within the former quarry pose a risk to groundwater.

Consequently, remediation is considered to be necessary. The GRA report is presented

in Appendix D.

9.6.3 Following the advice given in previous reports, we recommend that remediation takes

the form of bulk excavation of contaminated soils and onsite ex-situ bioremediation.

9.7 Excavation and treatment of hydrocarbon impacted soils

9.7.1 Soils are to be stockpiled in windrows a periodically turned to encourage bio-

degradation.

9.7.2 A separate method statement has been prepared regarding the excavation and

treatment of hydrocarbon impacted soils at the site (ref R-STG1772N-MS02-Rev01),

which is presented in Appendix E.

9.8 Remedial target concentrations

9.8.1 Due to the complexities in modelling hydrocarbons with the approach taken, remedial

targets for the ex-situ bioremediation were not presented within our GRA report (referto Appendix D for details).

9.8.2 Remedial target concentrations have been calculated using the Remedial Targets

Worksheet issued by the Environment Agency. All of the parameters used within the

GRA modelling have been used within the assessment to derive remedial targets




9.8.3 The following table presents the remedial target concentrations for each individual

aliphatic and aromatic hydrocarbon fraction.

Table summarising remedial target concentrations

Hydrocarbon

Fraction

Remedial target

concentration (mg/kg)

aliphatic >C5-C6 2.18

aliphatic >C6-C8 11aliphatic >C8-C10 86

aliphatic >C10-C12 684

aliphatic >C12-C16 13645

aliphatic >C16-C21 1.72E+06

aliphatic >C21-C35 2.72E+10

aromatic >C5-C7 0.22

aromatic >C7-C8 0.69

aromatic >C8-C10 4.32aromatic >C10-C12 6.84

aromatic >C12-C16 13



Table reference 9.8.3

9.8.4 At this stage, it is not clear where soils will be deposited following remediation. Once

the location of the placement has been chosen, the remedial targets presented abovemay require revision to maintain protection of receptors.

9.9 Monitoring and compliance

9.9.1 Laboratory testing will be undertaken on soil samples from the sides of the excavation

following removal of hydrocarbon impacted soils to confirm or otherwise that all

impacted soils have been removed. Testing will also be undertaken on the stockpiled

soils during the remedial process to monitor the effectiveness of such works. Testingwill be undertaken until compliance with the remedial target concentrations outlined

above has been achieved.

9.9.2 Soiltechnics Limited has consulted with the Environmental Health Officer at ENC

regarding the quantity and type of sampling/testing that will be deemed acceptable.




9.9.5 Hydrocarbon impacted soils excavated from the former quarry area will be treated on

site using ex-situ bioremediation methods (refer to Appendix E for details). A

composite sample will be taken for every 200m3

of soil excavated, with testing

undertaken at various stages of the remedial process.

9.9.6 Test results will be evaluated and compared directly with the relevant target

concentrations for each individual hydrocarbon fraction calculated from the Remedial

Target Spreadsheet. It has been agreed that the data will be assessed based on the

calculation of a 95% Upper Confidence Limit (UCL). The UCL provides an estimate of the

population mean, based on test data, with a 95% confidence that the actual mean does

not exceed this value.

9.9.7 If groundwater is encountered and is suspected to be contaminated it will be

channelled into an appropriately sized sump, with any free phase removed from the

water using absorbent ‘booms’. The remaining water shall either be tested to confirm

whether or not it can remain in the excavation or, pumped out and appropriatelydisposed of off site.

9.10 Soil sampling methods and laboratory testing

9.10.1 Soil samples for subsequent laboratory determination of concentration of chemical

contaminants will be taken from the sides of excavations using clean stainless steel

equipment and stored in an amber glass jar with a PTFE sealing washer, labelled and

sealed. The stainless steel sampling equipment was cleaned with deionised waterbetween sampling points.

9.10.2 If groundwater is encountered, samples will be taken from the excavation using new

proprietary plastic bailing equipment. The sample will be placed in a new amber glass

jar quickly sealed with a screw cap with a PTFE washer and subsequently labelled.

9.10.3 Sampling within stockpiled material and from the sides/base of the excavation will be

undertaken based on guidance presented in BS EN 932-1:1997 – “Testing for general

properties of aggregates” . Samples of equal size shall be taken from the stockpiles on

site at different points at different heights and depths over the complete stockpile,

subject to forming one composite sample per 200m3

of soil.

9 10 4 Drawings will be compiled during the remedial process which indicates the approximate




9.11 Backfilling remedial excavations and historic well

9.11.1 Remedial excavations are likely to be backfilled with site won material, either from

areas where reduction of levels are proposed or using remediated soils originally

excavated from the former quarry (subject to complying with remedial target

concentrations).

9.11.2 A detailed method statement which includes a specification for the backfilling of

excavations will be issued following further liaison and consultation with the structural

engineers on the project.

9.11.3 During the recent demolition of existing buildings on site, a 2.0m diameter, masonry

lined well was discovered underneath the floor slab of the former factory building. The

well measured a depth of 9.0m, with water recorded a depth of 5.1m below existing

surface level (refer to Drawing PRS02 for position). The area surrounding the well has

been suitably fenced off at present to ensure the safety of any third party on site.

9.11.4 With reference to Drawing PRS03, the well is positioned within the footprint of a

proposed development. As such, the well will require appropriate decommissioning

and backfilling to ensure that the development can proceed in this area. As described

above, further liaison and consultation with the structural engineers on the project will

be required in order to present a specification regarding the decommissioning and

backfilling of the well.

9.11.5 Guidance presented in the Environment Agency document “DecommissioningRedundant Wells and Boreholes” will be followed in the production of any method

statement/specification. Such documentation will be issued in due course.



Residential development

Finedon Road, Irthlingborough

Site location Grid Ref 494150, 271290



Appendix ADefinition of geo-environmental terms

Definition of environmental r isk/hazard terms used in this report.

Based on CIRIA report C552 ‘Contaminated land risk assessment – A guide to good practice’. Potential hazard severity definition

Category Definition

Severe Acute risks to human health, catastrophic damage to buildings/property, major pollution

of controlled

waters

Medium Chronic risk to human health, pollution of sensitive controlled waters, significant effects

on sensitive ecosystems or species, significant damage to buildings or structures.

Mild Pollution of non sensitive waters, minor damage to buildings or structures.

Minor Requirement for protective equipment during site works to mitigate health effects,

damage to non sensitive ecosystems or species.

Probability of risk definition

Category Definition

High likelihood Pollutant linkage may be present, and risk is almost certain to occur in long term, or

there is evidence of harm to the receptor.

Likely Pollutant linkage may be present, and it is probable that the risk will occur over the long

term

Low likelihood Pollutant linkage may be present, and there is a possibility of the risk occurring, although

there is

no

certainty

that

it

will

do

so.

Unlikely Pollutant linkage may be present, but the circumstances under which harm would occur

are improbable.

Level of risk for potential hazard definition

Probability of

risk

Potential severity

Severe Medium Mild Minor

High Likelihood Very high High Moderate Low/Moderate

Likely High Moderate Low/Moderate Low

Low Likelihood Moderate Low/Moderate Low Very low

A di A




Definition of environmental r isk/hazard terms used in this report.

Based on CIRIA report C552 ‘Contaminated land risk assessment – A guide to good practice’. Risk classifications and likely action required: Very high risk

High probability

that

severe

harm

could

arise

to

a designated

receptor

from

an

identified

hazard

OR

there

is

evidence that severe harm to a designated receptor is currently happening. This risk, if realised is likely to

result in substantial liability. Urgent investigation and remediation are likely to be required.

High risk

Harm is likely to arise to a designated receptor from an identified hazard. This risk, if realised, is likely to result

in substantial liability. Urgent investigation is required and remedial works may be necessary in the short term

and are likely over the long term.

Moderate risk

It is possible that harm could arise to a designated receptor from an identified hazard. However, it is either

relatively unlikely that any such harm would be severe, or if any harm were to occur it is likely that the harm

would be relatively mild. Investigation is normally required to clarify risks and to determine potential liability.

Some remedial works may be required in the long term.

Low risk It is possible that harm could arise to a designated receptor from an identified hazard but it is likely that this

harm, if realised,

would

at

worst

normally

be

mild.

Very low risk

It is a low possibility that harm could arise to a designated receptor. On the event of such harm being realised

it is not likely to be severe.

A di A




Gaseous contamination -Extract copy of table 3 of BS8485:2007 Solut ions scores

PROTECTION ELEMENT/SYSTEM SCORE COMMENTS

a) Venting/dilution (see Annex A of BS8485)

Passive sub‐floor ventilation (venting layer can be a clear void or

formed using gravel, geocomposites, polystyrene void formers,

etc) A)

Very good

performance

2.5 Ventilation performance in accordance with

Annex A of BS8485.

Good

performance

1

If passive ventilation is poor this is generally

unacceptable and some form of active system

will be required.

Subfloor ventilation

with

active

abstraction/pressurization

(venting

layers

can

be

a

clear void or formed using gravel, geocomposites, polystyrene void formers, etc)A)

2.5

There have

to

be

robust

management

systems

in

place to ensure the continued maintenance of

any ventilation system.

Active ventilation can always be designed to

meet good performance.

Mechanically assisted systems come in two main

forms: extraction and positive pressurization

Ventilated car park (basement or undercroft) 4 Assume car park is vented to deal with car

exhaust fumes, designed to Building Regulations

Document

F

and

IStructE

guidance.

b) Barriers

Floor Slabs It is good practice to install ventilation in all

foundation systems to effect pressure relief as a

minimum. Block and beam floor slab 0

Reinforced concrete ground bearing floor slab 0.5

Reinforced concrete ground bearing foundation raft with limited service

penetrations that are cast into slab

1.5 Breaches in floor slabs such as joints have to be

effectively sealed against gas ingress in order to

maintain these performances. Reinforced concrete cast in situ suspended slab with minimal service penetrations

and water bars around all slab penetrations and at joints

1.5

Fully tanked

basement

2

c) Membranes

Taped and sealed membrane to reasonable levels of workmanship/in line with

current good practice with validation

B), C)

0.5 The performance of membranes is heavily

dependent on the quality and design of the

installation, resistance to damage after

installations, and the integrity of joints. Proprietary gas resistant membrane to reasonable levels of workmanship/in line

with current good practice under independent inspection (CQA) B), C)

1

Proprietary gas resistant membrane installed to reasonable levels of

workmanship/in line with current good practice under CQA with integrity testing

and independent validation.

2

d) Monitoring and detection (not applicable to non‐managed property, or in isolation)

Intermittent monitoring using hand held equipment 0.5 Where fitted, permanent monitoring system

ought to be installed in the underfloor

venting/dilution system in the first instance but

can also be provided within the occupied space

as a fail safe.

Permanent monitoring and alarm system

A) Installed in the underfloor

venting/dilution system

2

Installed in the building 1



Part of the BAUER group

Skimming Pump Trial for Soiltechnics

Irthlingborough

August 17

th

& 18

th

2010

Report of Trial and Findings

A 2” GRS pneumatic skimming pump was installed into a 2” monitoring well, in order to

evaluate the rate of oil removal from the well and the easy of recovery of the oil.

August 17th

The initial dips were taken by the Soiltechnics Engineer and reported as:

Depth to Oil (DTO) 6.98m

Depth to Water (DTW) 7.30m

Therefore the oil layer thickness in the well was 320 mm. This represented 0.6 litres within

the well. It was noted that this volume of oil would fill 8 meters of the 10mm product

discharge line utilised in the trial.

The skimming pump was inserted into the well such that the oil surface would be at its mid

travel point. The pump was operated for 20 minutes. No oil or water arrived at the surface

during this period.

The pump was removed and the float deliberately slightly submerged in order that it would

skim any oil at the surface, together with a small quantity of water. The pump was operated

for circa 10 minutes, after which there was no sign of further oil or water arriving at thesurface. The small sample of liquid pumped to the surface was inspected and it was seen that

there was a very small quantity of oil present: insufficient to form a uniform layer over the

surface of the water in a 1 litre sample bottle.

The pump was removed from the well and the well re-dipped. The readings were:-



11:48 The pump was removed and the well dipped. The values were:-

Time Depth to Oil Depth to Water Oil Thickness11:49 Not detectable 7.094 0 mm

This indicated that the water level in the well had been depressed by 7.094 - 6.990 = 104 mm

The recovery rate of the well was measured as follows:-

Time Depth to Oil Depth to Water Oil Thickness

11:49 Not detectable 7.094 0 mm





11:56 Not detectable 7.081 0 mm11:57 Not detectable 7.079 0 mm













13 00



The data recorded is plotted graphically as follows:-

August 18th, 2010 - Recovery Rate Trial - Irthlingborough

6.98

7

7.02

7.04

7.06

7.08

7.1

11:45 12:00 12:15 12:30 12:45 13:00 13:15 13:30 13:45 14:00 14:15 14:30 14:45

Time

D e p t h t o W a t e r

The key data observed were:-

1. With the water table at circa 7 m below surface and with a well level depression of

104 mm, the steady state water inflow rate was 2.22 litres/hour.2. The recovery time from 104 mm level depression was 2 hrs 56 mins.

3. Little oil was present in the well during these trials. Once all the oil had been removed,

negligible oil returned to the well. There was a thin smear of a dark coloured oil on the

end of the probe, but this was insufficient to be detectable.

It should be noted that the water table was in a relatively impermeable layer of clay at the

time of these trials. It is recommended that the well is closely monitored when the water table returns to the more porous higher layer. Under these conditions, as the level rises and

falls, it is possible that more oil may migrate into the well, if it is currently trapped in domes

and troughs in the fractured rock in this layer. If significant oil does arrive at the well, such

that skimming were to be considered as a treatment option in the future, it is important to

collect a reasonable quantity of this oil (at least 2 litres) in order that its characteristics can be

Residential developmentFi d R d I thli b h





off

Finedon Road

IrthlingboroughNorthamptonshire

METHOD STATEMENT FOR DECOMISSIONING OF ABOVE

GROUND FUEL STORAGE TANK



Report originators

Prepared by


[email protected]


Supervised


FGS

[email protected]


Reviewed

Stephen Cragg B.Sc (Hons)., [email protected] Director, Soiltechnics Limited

Report issue



Residential developmentFinedon Road Irthlingborough





off

Finedon RoadIrthlingborough

Northamptonshire

METHOD STATEMENT FOR REMEDIATION OFHYDROCARBON CONTAMINATED SOILS



Report originators

Prepared by


[email protected]


Reviewed

by


FGS

[email protected]


Report issue



Residential developmentFinedon Road Irthlingborough




Remediation of hydrocarbon impacted soils

As previously mentioned hydrocarbon impacted soils identified within the area of the former quarry

will be excavated and treated on site and potentially re-used on site. The use of windrows is

proposed for the treatment of hydrocarbon contaminated soils at the site. Such systems will allow

frequent aeration of the impacted soils, increasing microbial activity and encouraging

biodegradation of organic contaminants under aerobic conditions. Microbes will utilise the source

of carbon and energy within the contamination and degrade it, with carbon dioxide and water being

the major waste products.

The excavated hydrocarbon impacted soils will be placed into shaped piles generally between 1.5m

and 2.0m in height and up to 6.0m in width. Soils will be placed onto an impermeable membrane to

prevent hydrocarbons leaching into soils below. The membrane will be bedded on a layer of sand to

prevent it being pierced on rough ground during periods of turning. We also recommend that a

layer of sand approximately 300mm in thickness is placed on top of the membrane acting as a

marker layer which should prevent the membrane being pierced by machinery. The sand will also

absorb any potential free-phase hydrocarbon contamination and contaminated water which is

contained in the soil. An impermeable bund will be required around the perimeter of the windrows

in order to prevent potential migration of free phase contaminants. Windrows should also be

covered with an impermeable membrane to prevent leaching of contaminants through percolation

of rainwater.

It should be noted that such remediation requires ambient air temperatures to be at a certain level

which will promote the degradation of organic contaminants. During cooler periods of weather, the

decrease in temperatures may ‘kill off’ any microbes at the surface of the windrow. Furthermore,

the low internal temperatures and amount of oxygen within the windrow will cause microbes to

become largely inactive and decrease the eventual breakdown of hydrocarbons.

To improve aeration and speed up the process of degradation, soil organic amendments and

nutrients could be introduced to the windrows during periods of turning. Aeration pipes could also

be introduced to assist in the ventilation of contaminated soils during periods between turnings.

Stockpiles shall be formed depending on the degree of contamination based on visual and olfactorymethods on site. Soils which are deemed to exhibit minor concentrations of hydrocarbon

contamination will be placed into separate windrows to that of soils which exhibit highly elevated

concentrations of hydrocarbon contamination.

Remedial excavation




, g g

Re-use of hydrocarbon impacted soils

Following remediation of hydrocarbon impacted soils, additional testing will be undertaken to

determine whether remediation has been successful and soils can be potentially re-used as

engineered fill. Sampling and testing schedules will be issued following remediation. If laboratory

testing indicates contaminants in soils are still at concentrations which may be harmful to human

health and water receptors further remediation will be required. Remedial target concentrations for

soils have been derived using the Remedial Targets Worksheet issued by the Environment Agency.

Further details regarding the remedial targets derived and recommendations for monitoring and

compliance are presented in Section 9.9 of our Remedial Strategy Report (R-STG1772N-PRS01-Rev01).

It should be noted that soils overlying the hydrocarbon impacted material can be reused on site in

their existing condition. Such soils will, however, require inspection as excavations proceed to

confirm that no hydrocarbon contamination is present.

License requirements

The Environment Agency legislation requires a site waste management plan to be prepared for a site

which is to be subject to excavation and movement of contaminated soils.

The contaminated soils, following excavation, will be treated and potentially re-used on site. With

reference to the consultation document produced by the Environment Agency “Land remediation

and Mobile Treatment Licensing” the treatment of contaminated soils is a licensable activity. The

licence used to regulate this activity on site (either in-situ or ex-situ) is a Mobile Treatment License(MTL), as opposed to a site licence. It is understood that such licenses generally apply if remediation

of over 1000m3

of contaminated soils is proposed. As up to approximately 3500m3

of hydrocarbon

impacted soils are proposed to be excavated, a MTL will be required for the site, together with a

deployment form. Further advice and the relevant forms in order to apply for the license are

available from the Environment Agency website.

Method statement alteration/amendments

Any required alterations or amendments to this method statement should be agreed with

Soiltechnics Limited prior to commencing any works on site.

Method statement compliance

R-STG1772N-PRS01-Rev 01 (Excl App D).pdf

Documents

Transcript of R-STG1772N-PRS01-Rev 01 (Excl App D).pdf