Field Application of Resistivity and Spectral Time Domain IP to Investigate Geoelectrical Signatures of Free-phase PCE

Soils beneath former dry cleaning sites are often contaminated with the chlorinated hydrocarbons PCE and its degradation products, which are highly toxic and cancerogenic. In this study, resistivity and time domain induced polarization (DCIP) were measured at a former dry cleaning site in order to investigate if the source contamination of PCE could be detected. 80 meter long 2D-profiles were measured across the site with the ABEM Terrameter LS instrument. The DC and full IP decay data were inverted using the 2-D DC/IP inversion algorithm developed by Fiandaca et al. (2013), giving access to the spectral information contained in the IP decays. The inversion parameters DC resistivity (ρ), chargeability (m0), the relaxation time (τ) and the frequency factor (C) were compared to reference data from boreholes. The reference data consisted of geological classification and concentration of free-phase chlorinated hydrocarbons, obtained from soil samples. A high resistive anomaly was observed at a location along the profile where soil sampling have confirmed high concentrations of free-phase chlorinated hydrocarbons. High IP-effects, in terms of the spectral parameters m0 and C, was seen next to this area. It is suggested that the IP-effects arise in a zone next to the free-phase source plume.