BROWNFIELD & CONTAMINATED LAND - Welcome to RSK Geophysics

The UK Government has set a target of 60% for all newdevelopments to be built on brownfield sites. Thesesites frequently contain poor ground conditions and aplethora of unknown underground obstacles which maycause costly engineering and environmental issues anddelays to the developer if they remain undetected.

Geophysical techniques can play an important role inreducing costs and risks by providing rapid sitereconnaissance surveys to characterise subsurfacefeatures prior to any intrusive investigation.

Rapid data collection rates (up to 2 hectares or more perday), and specialist data processing techniques, meanthat preliminary results can usually be offered soon afterthe completion of a survey, providing an invaluable toolin the reduction of risk from unforeseen groundconditions.

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BROWNFIELD & CONTAMINATED LAND

Data ExamplesThe data was recorded over a former industrialsite that was proposed for a new power station. As partof a gas pipeline route investigation, a multi-disciplinerygeophysics investigation was carried out to determinethe presence and location of all below ground services,foundations, geological constraints and otherobstructions that would render it infeasible to lay a largediameter steel gas pipe. The resulting GPR andelectromagnetic surveys clearly identified whichstructures remained in-situ and which had beenremoved. The resultant utilities drawing showing all thehazards crossing the proposed route providedinvaluable information, with the final phase ofverification of the geophysical results by trial trenching.

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Services

Slabs

Metal gas pipes

EM61 data

Results ofutility survey

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Seismic Refraction and ReflectionSeismic Surface WaveSelf Potential (SP)Induced Polarisation

Geophysical Techniques Available]

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Ground Penetrating Radar (GPR)EM Ground Conductivity

] Electrical Resistivity ImagingMagnetics SurveyingMicrogravity

For further information, visit us at www.rsk.co.uk or contact:George Tuckwell: [email protected] (Tel: +44 (0)1442 416656)

Former Land Use Determination

As part of geoenvironmental site investigations,determining the former land use of a site canprovide a useful base for determining the likelysources and locations of contamination and/orobstructions prior to re-development. Historicalmaps and other desk study data are a vitalsource on information, but do not reveal whetherthe structures are still present, and can beambiguous.

Locating metal pipes usingMagnetic Gradiometry

In this example to the , the client wasunaware of the location of two deep metalpipelines running beneath a supermarket carpark. Geophysics was used to locate thepipelines so the proposed building extensioncould be built around them.

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Scale (metres)

0 5 10 15

Locating buried services and obstructions

In this example to the left, EM mapping was used to offer a quickscreening tool producing site-wide rapid characterisation of aderelict engineering works for the purpose of detectingunderground hydrocarbon tanks for further investigation.

The EM map ( ) clearly highlights problematic groundconditions and areas containing buried foundations,

utilities and storage tanks .

The data also shows how surface featuressuch as metal fences and metal objects

such as benches and vehicles canstrongly affect the data. In sites

with too much above groundclutter, anomalies from

sub-surface featuresmay be masked and

not be detected.

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Key features

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Piled foundations

Underground tanks

Large underground gas mains

Other buried services

Metal surface features

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High amplitude linear magnetic anomaliesindicative of buried metal services

High amplitude discrete anomalies causedby surface trolley parks

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INFERRED PIPELINE ROUTE

Reds and pinks showareas of highestconductivity



Key features

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Buried in-situe concrete foundations

Underground metal tank

Buried metal pipes

Potential pollution plume

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highest appare

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Scale (metres)

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Site characterisation

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Site characterisation is the first and most important step in brownfield site and contaminated land investigation.Features missed by conventional site investigation techniques can be identified in the initial stages by geophysics. Acomprehensive understanding of the ground conditions and contamination issues at a site is vital to the process ofproducing an accurate and cost-effective remedial strategy. Where risk assessment requires total site coverage totrace all possible sources and pathways of contamination the use of geophysics should be considered.

In this example , EM ground conductivity was used to offer a quick screening tool producing site-wide rapidcharacterisation of a site which had been demolished entirely to ground level. All structures below ground wereunderstood to have been removed, but the EM data clearly showed otherwise.

The results clearly highlight potential sources of contamination such as tanks and utilities, subsurface pathways likeburied foundations of former structures and also an area of possible contamination where a broken pipe had leaked tothe surrounding ground. This information was used to inform the subsequent intrusive investigation and dictate thebest location for targeted trial pits and boreholes.

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Mapping contamination

Mapping variations in the electrical across a site canhighlight anomalously conductive targets such as metallic tanks, pipework and alsoany ground contamination. Although water is generally not a good conductor ofelectricity, groundwater - especially contaminated groundwater - contains dissolvedcompounds and ions that greatly enhance its ability to conduct electricity.

conductivity of the subsurface


Hut

Hut

Metal Fencing

Response(mV)

Dist (m)Detecting old buried tanksand petrol contamination

In the example , the EM data show anarea of highly conductive ground adjacent to anumber of tanks at a former petrol station.LNAPL plumes can become more conductivewith age due to biodegradation. A subsequentintrusive ground investigation of the siterevealed the presence of increased levels ofhydrocarbon contamination.

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Contaminated Land Investigations

As part of the Part IIA regime, all potentiallycontaminated sites in the UK need to be investigated.

The use of geophysical techniques is an invaluable toolin the investigation of contaminated sites and can beused as rapid site reconnaissance tool without theexposure of site personnel to the hazards ofcontaminated sites.

Geophysical techniques can form an integral part of thesite investigation at all stages, from theinvestigation to highlight areas of potential contaminationto target conventional intrusives; to the main Phase 2investigation to augment and confirm boreholeinformation to improve the Conceptual Site Model;through to the latter phases such as the monitoring andvalidation of remedial measures.

preliminary Phase 1

Broad hyperbolicreflectors in the radar

data confirm thepresence of USTs

Plume

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Locating heavy hydrocarbon contamination

Location of USTs

In this example , RSK was appointed to helpwith the delineation of a spillage of crude oil from atanker loading station. Hydrocarbons are excellentinsulators – as a result have very high values ofresistivity. For this reason, we can use the resistivitytechnique to locate Hydrocarbon contamination inthe ground.

The resistivity data shows the existence of dippinghigh resistivity anomalies – coloured reds andpurple – that shows where the heavy DNAPL oil ispresent within fractures in the sandstone bedrock,constrained by marl below. This information helpedto identify where to concentrate subsequentinvestigations and remedial works.

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Documents

BROWNFIELD & CONTAMINATED LAND - Welcome to RSK Geophysics