The effect of free-phase NAPL on the spectral induced polarization signature of variably saturated soil

In this study, the influence of a free phase nonaqueous phase liquid (NAPL), decane, on the soil's SIP signature was experimentally investigated. The complex electrical conductivity was determined using the SIP measurement system and compared between two main treatment types: clean and decane contaminated. Complementary chemical and temporal measurements were conducted. The results show a clear decrease in the imaginary part of the complex conductivity for the decane contaminated soil. Moreover, a shift of the relaxation frequency was observed for the contaminated soil. Our chemical analysis suggests that there was no change in the chemical composition of the Stern layer, and clearly, the grain size distribution did not change as well. Therefore, these results are attributed to membrane polarization. The decane addition to the unsaturated porous media changes the pore-scale liquid phase distribution, thus affecting membrane polarization. Further, the electrical signature is a time-related process associated with liquid phase arrangement time. The findings of this study can enable a better understanding of the SIP response for soils contaminated with free-phase organic compounds.