Early Evidence for Complex Resistivity as a Geophysical Field Method to Delineate PFAS Contamination
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The distribution of polyfluoroalkyl substances (PFAS) in aqueous film forming foam (AFFF)-impacted source areas remains poorly understood, despite the growing urgency to deal with PFAS contamination. New field methods to delineate and characterize source zones are needed to better understand the fate of these contaminants in the subsurface, and to better assist with site management and future remediation efforts. While direct sampling and laboratory analysis for PFAS constituents are possible, these efforts result in sparse sampling of the affected area. Geophysics has the potential to provide a means to characterize AFFF-impacted source zones on a more relevant spatial and temporal scale than direct sampling. The imaginary conductivity (s’’) as measured with Complex Resistivity (CR) measurements is sensitive to changes in surface charge associated with cation sorption. As PFAS is known to closely associate with the pore surface, CR seems a likely choice to study environmental PFAS contamination. To assist with the ongoing effort to better address PFAS contamination, we explore the potential for CR to characterize PFAS contaminated source zones through a series of bench-scale experiments and field surveys.
In bench-top studies we have observed promising trends in synthetic and legacy contaminated soils indicating that s’’ is sensitive to the presence of PFAS contamination. We have also observed trends in soils treated to remove PFAS that further indicates sensitivity of s’’ to PFAS concentrations. In addition to laboratory data, we present early field evidence that CR surveys can delineate variations in PFAS concentrations associated with a legacy source zone of contamination.