INDUCED POLARIZATION RESPONSE FROM THREE PER-AND POLYFLUOROALKYL SUBSTANCES (PFAS) IMPACTED FIRE TRAINING SITES
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The development of field-scale, in situ screening technologies is crucial for assessing aqueous film forming foam (AFFF) source zones at former fire training sites, which are long-term sources of per- and polyfluoroalkyl substances (PFAS) contamination. Induced polarization (IP) may offer sensitivity to AFFF contamination due to the sorption of PFAS compounds and PFAS precursors to mineral surfaces. We performed laboratory measurements to determine the sensitivity of IP to AFFF contamination in both synthetic sediments and natural soils obtained from three different AFFF source zones. Laboratory measurements were also made on synthetic soils contaminated with a zwitterionic PFAS precursor. We also performed field-scale IP imaging across the three different AFFF source zones.
Experiments on synthetic soils reveal the IP response of AFFF contaminated soils is likely dominated by the cationic and zwitterionic precursors that are strongly sorbed to soil mineral interfaces. For natural soils, a statistically significant linear relationship between total PFAS concentration and laboratory-measured IP response was observed for one homogeneous undisturbed source zone. A visual correlation between field IP response and sample PFAS contamination was noted but not statistically significant. In contrast, no significant relationship between IP response and total PFAS concentration was found across two heterogeneous AFFF source zones despite the availability of an extensive set of soil samples (>70 samples). Instead, the IP response was dominated by the lithologic variability between these source zones, as indicated by a significant relationship between IP response and soil surface area.
These findings indicate that IP might provide a rapid and cost-effective means to map variations in contamination across AFFF source zones, guiding the selection of soil sampling locations and minimizing the risk of missing PFAS hotspots. However, the use of IP to map variations in PFAS concentration will be restricted to sites with minimal heterogeneity. Otherwise, the IP response will be dominated by lithologic variations across the site. In this case, the opportunity exists to use IP to determine field-scale realizations of soil surface area heterogeneity, which is critical information needed to calibrate recently developed models for predicted PFAS leaching rates from AFFF source zones.