Identifying PFAS transport pathways during pluvial flooding using surface water modelling in Gorsingeholm

Sammanfattning

Per- and polyfluoroalkyl substances (PFAS) pose severe global risks to drinking water due to their persistence and high aquatic mobility. At the Gorsingeholm water treatment plant in Strängnäs, Sweden, PFAS concentrations in raw intake water from Lake Mälaren exhibited low concentrations yet spiked to heightened levels following initial artificial infiltration for managed aquifer recharge (MAR). Because the basin infiltration materials themselves were uncontaminated, this study aimed to investigate the unknown surface runoff and depression-focused groundwater recharge pathways connecting surrounding land uses (LUs) to the water treatment plant. Hydrological modelling for 10- and 100-year rain events was conducted using ArcGIS Pro, and two modelling methods; PluvioFlow and a re-creation of SCALGO Live’s methodology within ArcGIS Pro. The hydrological findings were subsequently cross-referenced with industry-specific PFAS usage identified in scientific literature Hydrological findings reveal that surface runoff watersheds contributing to the water treatment plant generally expand as the analysed buffer area increases. Runoff most likely originates from LUs to the southeast, specifically a cereal industry and a farmstead/SME property. However, under the largest analysed precautionary buffer zone, runoff pathways extended up to 8 km southwest, incorporating vast agricultural fields. Conversely, potential groundwater recharge zones generally exhibit larger spatial extent during the 100-year rain event and are heavily concentrated within flat agricultural fields. Volumetrically, two massive agricultural fields dominate the total potential groundwater infiltration largely due to their sheer spatial scale. However, smaller LU areas also contribute substantial total infiltration volumes due to high infiltration intensities relative to their size. Integrating these identified water pathways with scientific literature on land use specific PFAS signatures highlights potential risk profiles. The cereal industry is associated with potential ground pollution and pesticide applications, while the Farmstead/SME may be associated with PFAS contamination in soil and sediments. Furthermore, agricultural fields present risks via application of sewage sludge and specific pesticide treatments. While the measured concentrations are overall low, and a definitive point source could not be isolated, the study’s aim of providing insight about potential PFAS pathways and sources, via surface runoff and groundwater recharge, were fulfilled. Ultimately, this research identifies the cereal industry (primarily via surface runoff) and the farmstead/SME (via both runoff and recharge) as the highest priority targets for future empirical sampling.