Key features

Geophysical Techniques Available]

]

]

]

]

Electrical ResistivityElectromagnetic Mapping (EM)Ground Penetrating Radar (GPR)Self PotentialMagnetic Gradiometry

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

The use of geophysical techniques is an invaluabletool in the investigation of contaminated sites and canbe used 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 the

investigation to highlight areas of potentialcontamination to target conventional intrusives; to themain Phase 2 investigation to augment and confirmborehole information to improve the Conceptual SiteModel; through to the latter phases such as themonitoring and validation of remedial measures.

preliminary

Phase 1

GPGP

IC

EJB

WM

WM

IC

SF h 2.5

SF h 2.5

SF

h 2

.5

IC

IC

SF h

2.5

IC

IC

SF

h 2

.5S

F h

2.5

SF

h 2

.5S

F h

2.5

SF

h 2

.5

BW

h 2

.8

LP

G

IC

LP

G

IC

LP

IC

IC

B

B

LP

G

G

IC

G

SF h

2.5

LP

LP

LPIC

IC

SF h 2

.5

SF h 2

.5

LP IC

EJB

SPP

P

IC

IC

HR h 1.1

IC

IC

GSP

IC

CTVIC

IC

IC

CTV

CTV

G

SP

LP

LP

G

G

G

G

IC

G

G

G

G

SB

SP SB

SP

SP

G

G

G

IC

G

G

G

G

G

SP

G

GSB

G

IC

IC

SB

G

G

G

G

G

g 0.8s 8h 12

g 0.8s 8h 12

g 1.8s 9h 17

SB

GP

GP

Tarmac

FB

71.8

2

71.7

971.8

171.8

2

71.6

0

71.5

9

71.5

5

71.5

8

Tac

Grass

74.05

74.26

GP

G

Tarmac

Tarmac

Tarmac

Tarmac

Tarmac

Tarmac

Tarmac

Tarmac

Foundation

M U N

D E L

L S

M U N D E L L S

M U

N D

E L

LS

M U

N D

E L

LS

M U

N D

E L

LS

M U

N D

E L

LS

M U N D E L L S

H E R N S WA

Y

WA

TE R

S I

D E

Underpass

Beneath Road

Grass

Gravel

Canopy Line Ave

rage H

eight 15m

SF h 2.5

Canopy L

ine

Avera

ge H

eig

ht 5

m

BW

h 2

.8B

W h

2.8

G

G

Shrubs

Shrubs

Grass

Grass

Grass

Grass

Tarm

ac P

ath

& C

ycle

Lane

Tarm

ac P

ath

& C

ycle

Lane

(Brick)

Unidentified

Unidentified

Unidentified

A

B

C

D D

D

E

A

B

C

D

E

Buried foundations, including pile locations

Underground metal tank

Other buried obstructions

Buried services and sewers

Potential pollution plume

Reds and p

inks sh

ow are

as of

highest appare

nt conducti

vity.

Site characterisation

Site characterisation is the first and mostimportant step in contaminated landinvest iga t ion . Features missed byconventional site investigation techniques canbe identified in the initial stages bygeophysics. A comprehensive understandingof the ground conditions and contaminationissues at a site is vital to the process ofproducing an accurate and cost-effectiveremedial strategy. Where risk assessmentrequires total site coverage to trace allpossible sources and pathways ofcontamination the use of geophysics has to beconsidered.

In this example to the , EM groundconductivity was used to offer a quickscreening tool producing site-wide rapidcharacterisation of a site which had beendemolished entirely to ground level.

The results clearly highlight potential sourcesof contamination such as tanks and utilities,subsurface pathways like buried foundationsof former structures and also an area ofpossible contamination where a broken pipehad leaked to the surrounding ground. Thisinformation was used to inform thesubsequent intrusive investigation and dictatethe best location for targeted trail pits andboreholes.

left

Scale (metres)

0 10 20 30

Survey examples

Identifying land use with electromagnetics

Page 30

STATS GeophysicalPorterswood House

Porters WoodSt Albans, Herts

AL3 6PQ

CONTAMINATED LANDGEOPHYSICAL

Locating pollution plumes withintegrated geophysical techniques

In this example to the , EM conductivity andresistivity imaging were used to detect thepresence of possible buried tanks andcontamination present in the ground at a formerchemical works. Prior to the geophysicalsurvey, high concentrations of DNAPL carbondisuphide were recorded in soil samples takenfrom the ground. The EM and resistivity bothsuccessfully located a buried reinforcedstructure which has likely led to the pooling ofthe DNAPL in the vicinity. The results of thegeophysics aided the subsequent riskassessment and remediation of the site in orderto render it fit for purpose.

left

Hut Hut

WC

Meta

l F

encin

gM

eta

l F

encin

g

KnownManholeCovers

Response (mV)

Conductive targ

ets

Resis

tive targ

ets

Distance (m)

Mapping contamination

Mapping variations in the electricalacross a site can highlight anomalously

conductive targets such as metallic tanks, pipeworkand also any ground contamination.

Although water is generally not a good conductor ofelectricity, groundwater - especially contaminatedgroundwater contains dissolved compounds and ionsthat greatly enhance its ability to conduct electricity.

conductivity of thesubsurface

A

B

Location of underground tanksor reinforced structures

High conductivity anomaly delineatingpossible plume of contaminants

Detecting buried tanksand hydrocarboncontamination

In the example , the EM datashow an area of highly conductiveground adjacent to a number oftanks at a former petrol station. Asubsequent intrusive groundinvestigation of the site revealedthe presence of increased levelsof hydrocarbon contamination.

right

Broad hyperbolicreflectors in the radar

data can confirmthe presence of USTs

UST UST UST UST

STATS GeophysicalPorterswood House

Porters WoodSt Albans, Herts

AL3 6PQ

CONTAMINATED LANDGEOPHYSICAL

CR

OM

ER

GA

RD

EN

S

FARN

DALE

AVENU

E

2

1

11

15

4

68

10

12

35

79

Scale (metres)

0 10 20Apparentconductivity

(mS/m)

B

A

B

Resistivity:

Conductivity:

Low High

X

X

Y

Y

B

A

A

Page 31