Field measurement and modelling of PFAS leachability from a contaminated fire training area - whole of pad response...

Per- and polyfluoroalkyl substances (PFAS) have historically infiltrated concrete and asphalt pavements where aqueous film forming foams (AFFF) were used. These pavements can act as long-term sources of PFAS-contaminated runoff, but their contribution is not well quantified. Over 230 rainfall-runoff samples were collected over 335 days from a PFAS-impacted fire training area (FTA) and analysed for 32 PFAS. Rainfall and discharge were monitored, with peak runoff at 1.75 L/s across ∼30 events. Average total PFAS concentrations in runoff events were similar over 11 months (typically 1.0-3.8 µg/L; PFOS 0.50-1.7 µg/L). Within flow events, concentrations decreased at high flows, likely due to dilution, and increased as flows subsided. Composition was consistent throughout, with PFOS dominant (40-60 %) and PFHxS, 6:2 FTS, and PFHxA each ∼3-20 %. Even after long dry periods, PFAS profiles were unchanged. Annual PFAS discharge was estimated at 75-380 mg/y, with uncertainty at low flows. PFAS at greater than 1 µg/L might discharge over centuries based on estimates of the total mass. Similarly, modelling showed that PFAS might discharge for many decades to centuries. Findings suggest that natural release rates may not meaningfully reduce PFAS discharges over time, thus informing decisions on whether active remediation (e.g., removal, sealing, or water treatment) is warranted at legacy sites.