In the built environment engineered surfaces or infrastructure (e.g: roads, pavement, houses) often prevent electrode emplacement.
However,s large volumes of ground can still be scanned beneath buildings if tomographic measurements are made between two or more boreholes using cross-hole, single in-hole and surface-to-hole electrode arrays.
New 3D tomographic survey, data optimization and inversion schemes have been developed which have significantly improved detectability, image resolution and the accurate recovery of target geometry.
These new schemes were developed primarily to assist the detection of buried mine entries or shafts for the Coal Authority (see Figure 1).
Conventional cross-hole scanning failed to detect this shaft.
Research is on-going to assess the use of ALERT and CRT techniques to map the spatial and temporal distribution of subsurface contaminants before, during, and after in-situ remediation.
Geoelectric tomography has the ability to visualise dynamic processes including contaminant transport, and hydrochemical or biochemical reactions.
Permanent in-situ electrode arrays were installed in shallow boreholes below a car park built on a former gasworks site in Stamford, Lincolnshire. This buried installation permitted the remote, real-time, volumetric imaging of the site from the office without impeding the operation of the car park (Figure 2).
Such images can help to target injection points for reactive agents and to assess the longevity of remediation methods. This work was undertaken with South Kesteven District Council and Interkonsult Ltd with a DTI (now TSB) technology grant and industrial co-funding from VHE Construction Ltd.
This research, which was completed in 2009, demonstrated that ALERT monitoring can be used to remotely assess improvements in water quality during and after clean-up.
Contact the Geophysical tomography team