At Department of Defense (DoD) facilities in the United States (US), there are at least 650 former fire training areas where aqueous film-forming foam (AFFF) was applied, resulting in per- and polyfluoroalkyl substances (PFAS) impacts to surface water and groundwater. In order to effectively prioritize these sites for further investigation and/or remediation, standardized tools are needed to rapidly assess retention, leaching, and transport of PFAS from the source zone to down gradient regions. Existing standard leaching methods, developed prior to concerns regarding PFAS, may or may not adequately address the leaching of these species. Therefore, studies are needed to ensure that methods are compatible with PFAS and that resulting data are representative of the risk of PFAS leaching at impacted sites. Results of leaching evaluations (i.e., source terms) will be indicative of source zone behavior, which is likely to differ from PFAS mobility under saturated, down gradient conditions. Therefore, detailed site characterizations will need additional input including sorption/desorption coefficients (e.g. Kd). To date, sorption studies have focused on a limited set of PFAS relevant to AFFF-impacted sites. Further, studies have concluded that PFAS sorption is not correlated with a single sorbent characteristic (e.g., foc). Additional studies are needed to understand sorption of a broader suite of PFAS, and models should be developed that predict sorption coefficients based on multiple soil characteristics.

To meet these needs, the overarching goal of this project is to develop a framework for evaluation and prediction of the release of PFAS from AFFF-impacted media. The specific objectives include 1) development of a standard leaching assessment methodology for AFFF-impacted media; 2) utilization of approaches including high resolution mass spectrometry (HRMS), mid-infrared spectroscopy (MIR), and chemometrics to evaluate and develop a predictive model of PFAS sorption and desorption to AFFF-impacted media; and 3) comparison of results of laboratory testing to leaching and mobility under field relevant conditions to develop an approach for translation of bench-scale test results to site-scale implications.

The objectives will be achieved through a combination of bench-scale, field-scale, and modeling efforts. Specifically, standard methods included in the US Environmental Protection Agency Leaching Environmental Assessment Framework (LEAF) will be optimized for use with PFAS (Objective 1). A combination of HRMS, MIR, and chemometrics will be used to evaluate sorption of a broad suite of AFFF-relevant PFAS and develop predictive models of sorption to representative sorbents (Objective 2). Lastly, lysimeter data collected from ongoing SERDP efforts will be combined with mesocosm experiments, and results will be compared to laboratory leaching data to demonstrate the applicability of standard tests to PFAS leaching under environmental conditions.

The overarching benefit of this work will be the generation of techniques that can be used to support prioritization and management of the numerous AFFF-impacted sites within the DoD, thus reducing the overall risks to human health and the environment due to PFAS exposure. This will be achieved through development of pragmatic tools for understanding and evaluating PFAS leaching and mobility, which is essential for screening assessments, detailed risk assessments, and evaluation of treatment alternatives. Other benefits include further elucidation of the occurrence of a broad suite of newly identified PFAS at AFFF-impacted facilities. Lastly, methods developed in this work for use with AFFF-impacted media will have potential applicability in other PFAS-impacted media such as biosolids and municipal waste and thus are likely to be of broad interest and relevance to regulators and practitioners both within the U.S. and internationally. (Anticipated Project Completion - 2025)

Stults, J. F., C. E. Schaefer, Y. Fang, J. Devon, D. Nguyen, I. Real, and J. L. Guelfo. 2024. Air-Water Interfacial Collapse and Rate-Limited Solid Desorption Control Perfluoroalkyl Acid Leaching from the Vadose Zone. Journal of Contaminant Hydrology, 265:104382. doi.org/10.1016/j.jconhyd.2024.104382.