Transport and Transformation of PFASs in an Aqueous Film-Forming Foam-Impacted Fractured Rock Aquifer

Per- and polyfluoroalkyl substances (PFASs) occur in aqueous film-forming foams (AFFFs) used to extinguish jet fuel fires. Spatiotemporal behaviors of PFASs in fractured rock aquifers (FRAs) are virtually unknown, prompting this study of PFAS transformation and advective transport downgradient of AFFF applications that occurred in ∼1980–2017. PFAS concentrations in 60 water wells indicate spatial variability, from fluorotelomer sulfonate (FTS)-dominated proximal wells to downgradient wells dominated by perfluorocarboxylic acids (PFCAs); shorter-chain perfluorohexanoic acid (PFHxA) and perfluoropentanoic acid (PFPeA) are prevalent at intermediate distances, while longer-chain perfluorooctanoic acid (PFOA) is prevalent in distal wells. Perfluorooctanesulfonic acid (PFOS) and related sulfonates and sulfonamides are generally an order of magnitude lower in concentration than PFCAs. Temporal variability (2018–2023) is indicated by changing PFAS ratios over time, notably decreasing 6:2 FTS paired with increasing PFHxA and PFPeA. The prevalence of 6:2 FTS in groundwater indicates the need to quantify precursor PFAS compounds in drinking water and aquatic ecosystems.