3D Resistivity and Ip Tomography As Efficient Tools To Monitor Remedial Actions Over A Gas Plume

Last year, we assessed the efficiency of 3D resistivity tomography to delineate a hydrocarbon contaminated area situated near a gas station at Brugelette, Belgium. The site subsurface consists of dolomitic bedrock which is overlaid with 5 to 9 meters of clayey sands. The fresh hydrocarbon plume was detected through an increase in resistivities plotted especially on the modelled groundwater table. Geophysical investigations results were consistent with boreholes data and samples analyses. To cleanse groundwater at the site, 9 pumping wells were drilled in contaminated areas. In order to evaluate the efficiency of remedial actions, three 3D cross-diagonal resistivity and induced polarization surveys were conducted within seven months. Data were inverted using Res3DInv, resampled within Matlab and plotted on the modelled rockhead topography and water table. 3D resistivity tomographies showed higher resistivities in hydrocarbon-contaminated areas. Lithologic variations on the site do not stand out on IP tomographies. Moreover, hydrocarbon-impacted areas showed strong IP response compared to clean soils. Finally, time-lapse resistivity and IP tomographies revealed very efficient tools to follow hydrocarbon plume movements and to assess the efficiency of remedial actions.