Exploration of PFAS Mass Discharge in Stormwater Versus Groundwater: Technical and Regulatory Considerations

ABSTRACT At potential source areas of per‐ and polyfluoroalkyl substances (PFAS), a current priority is to delineate and control the risk of exposure of groundwater aquifers to PFAS. However, with the combination of mobility and persistence of some PFAS, the stormwater migration pathway may also pose risks to potential receptors. This study (1) analyzes the environmental criteria that may drive stormwater remediation, (2) models the stormwater hydrologic response of hypothetical aqueous film‐forming foam (AFFF) sites, (3) compiles perfluorooctane sulfonic acid (PFOS) concentration data in stormwater, and (4) compares the potential PFOS mass discharge in stormwater versus groundwater. Results indicate that typical stormwater mass discharge of PFOS was relatively smaller than groundwater contributions at AFFF sites. However, given the faster impact timescale of stormwater movement and the variability in receiving water types and uses, many AFFF sites may require some form of stormwater management. As PFAS in stormwater represents a relatively new environmental challenge, regulatory approaches and management strategies are expected to evolve over time, adapting to new research findings and site‐specific conditions. This paper presents a series of potential regulatory approaches for PFAS‐impacted stormwater, including expansion of existing regulatory programs, use of best management practices (BMPs), individual site mass discharge limits, and watershed‐scale PFAS mass balance approaches.