In-depth site characterization of poly- and perfluoroalkyl substances at an abandoned fire protection training area, An

Abstract

Poly- and perfluoroalkyl substances (PFASs) are a class of environmentally persistent fluorinated chemicals that are utilized in fire fighting, as well as other applications. PFAS contamination has been reported in groundwater and soil at several fire protection training areas (FPTAs) at concentrations well above provisional health advisory levels as a result of aqueous film forming foam application (AFFF). Many FPTAs have been remediated for fuel based contaminants that infiltrated the surface after years of training, but PFAS are still detected at high levels in groundwater and soil. AFFF was used at many FTPAs and understanding PFAS contamination at a typical site is the first step in understanding the potential environmental impacts of AFFF usage at FPTAs. The main objective of this study was to conduct an in-depth site assessment of groundwater and soil PFAS contamination at an AFFF-impacted FPTA. This assessment included independent analysis of groundwater samples for select PFASs by four different laboratories. Results of statistical analysis show that some analytical challenges remain with respect to standardizing analysis of highly contaminated aqueous PFAS samples. Also included was a direct analysis of recently identified PFCA and PFSA precursors in groundwater, and the application of a recently-developed total oxidizable precursor (TOP) assay to help identify the extent of potential PFCA and PFSA formation in the subsurface. Precursor results illustrate that there should be concern about an increase in end-product PFAS contamination without the addition of a discreet source. As part of the site assessment, the collection of paired groundwater and subsurface soil samples enabled the determination of field-based solid-water distribution coefficients (i.e., apparent Kd) for several PFASs. Coefficients determined in this study were generally consistent with those reported in laboratory studies. A secondary objective of this study was to discern to what extent historical data on the occurrence and treatment of typical co-contaminants at AFFF-impacted sites (i.e., benzene) can be used to infer either the extent of subsurface plumes of PFAS and/or the conversion of select precursor PFASs to perfluoroalkyl carboxylic acids and perfluoroalkyl sulfonic acids. By creating a conceptual model of the site and determining the extent of PFAS contamination, there is a hope that the site can be used as a model for determining extent of contamination at similar sites. At this site it was found that, with the exception of perfluorooctane sulfonate, a previously characterized plume at a site can be used as a first approximation of PFASs contamination at the site, especially if the contaminants were co-applied. AFFF application at many FPTAs occurred over many years, with repeated infiltration to the subsurface. The high levels of PFASs detected at this site in groundwater and soil, at least 20 years after the final application of AFFF, are a cause for concern; especially with the potential toxicity of the chemicals for wildlife and humans. Further research needs to be done to understand the fate and transport of these chemicals in the subsurface and the impact that precursors may have on the total PFAS contamination at a site.