Keywords: transient electromagnetic sounding, groundwater pollution, geo-, electric monitoring, water pollution, remote monitoring, Australia, undulating terrain, sandy terrain
Remote monitoring of groundwater pollution using geo-electric techniques in undulating sandy terrain, Western Australia
Early-time transient electromagnetic sounding (TEM) and DC resistivity sounding techniques have been used to monitor remotely the changes with time of a groundwater pollution plume at a test site on a sand aquifer. A range of techniques for interpretation of TEM sounding data have been evaluated. All of these were successful in identifying expansion of the plume. The most plausible interpretation of TEM data was achieved using a 3-layer inversion model, with fixed parameters (resistivity, depth) for layer 1 – the unsaturated zone. Resistivities of layer 2, the saturated zone, were resolved reasonably well, and indicated the general position of the plume, and its expansion with time. TEM, however, did produce artificial dispersion of the plume, due to the large volume of aquifer (at the test site) contributing to the signal. We could see little practical advantage in the extensive use of joint TEM and DC-resistivity soundings. We conclude that, although the technique was reasonably successful in identifying pollution, there is considerable scope for improvement in the operation and interpretation of early-time TEM soundings. This should lead to more precise identification of changes in formation resistivity due to pollution in shallow groundwater. This inevitably will lead to more cost effective assessment of the impact of sources of pollution on groundwater, by reducing the need for extensive networks of monitoring boreholes.