Induced Polarization Signatures at Former Fire Training Areas
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The release of PFAS containing aqueous film-forming foam (AFFF) constituents from former firefighting training areas leads to soil and groundwater contamination, threatening human health, the environment, and access to clean water. Non-invasive field methods are needed to effectively characterize soil PFAS concentrations, textural variations, specifically soil surface area, and to model long-term PFAS leaching from these source zones. Non-invasive geophysical methods, such as induced polarization (IP), can characterize the electrical properties of the subsurface. Preliminary research indicates that IP has the potential to detect variations in sorbed AFFF constituents. However, IP is also highly sensitive to soil texture (as quantified from surface area or grain size) such that textural heterogeneities at field sites may mask signals from sorbed AFFF constituents. This study investigated the contributions of AFFF contamination versus soil surface area to IP signals observed across two former firefighting training areas. Samples were collected to assess the statistical significance of IP sensitivity in distinguishing AFFF sorption from soil surface area variations through laboratory analysis. Results indicate the IP measurements could not resolve the spatial variations in soil PFAS concentrations at these sites. Importantly, this study highlights the capability of IP to image field-scale variations in surface area and the non-invasive field scale utility of geophysics to understand PFAS leaching from contaminated source zones through the mapping of soil textural variations.