Environmental Geophysics

Introduction

In contaminated land studies, geophysical surveys can expedite site characterisation by providing 2D/3D images of changes in physical contrasts in the subsurface. Site screening is thus optimised in advance of follow-up drilling and sampling which, therefore, deliver a more effective and representative analysis of subsurface contamination.

Using geophysics, the risks of undetected targets are reduced and the overall costs of environmental clean-up may be significantly lowered.

Techniques

Surface: Gradient magnetics, electromagnetic profiling and sounding, electrical (resistivity and self potential) profiling and sounding, 2D resistivity and electromagnetic conductivity imaging, ground penetrating radar, seismic refraction, microgravity, radiometrics.

Applications...

Map Verification

Town water main mapped as blue line - actual position shown as negative EM in-phase component (blue)

Derelict Land Investigations

Manafactured gas plant investigation of car park showing evidence of structural remains, buried tanks, buried voids and contaminated ground - map shows combined EM in-phase and conductivity with mauve as relative highs

Investigation of derelict land - perspective view of terrain conductivity showing infilled trenches

Investigation of derelict land - underground storage tanks (UST) mapped as negative magnetic gradient anomalies

Investigation of derelict land - Raw GPR radargram - 900MHz data over 2 clay pipes beneath reinforced concrete.

Landfill Investigations

Landfill Modelling - 2D Resistivity Imaging

2D true resistivity model of landfill composed of saturated chemical waste materials - shown as resistivity low (blue) surrounded by higher resistivity alluvial materials

Microgravity model of landfill geometry - fill composed of loosely compacted builders rubble

Circle indicates position of 2mm hole in 5mm HDPE liner mapped through 0.5m of sand cover using electrical technique (mauve = high response)

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