LINGERS · Novel modeling methodology for per- and poly-fluoroalkyl substances and their precursors transport and fate in dune filtration systems

Sea spray aerosols (SSA) have been identified as a secondary emission source of per- and polyfluoroalkyl substances (PFAS), overturning the long-held belief that the ocean serves as a final sink for these persistent, EU-regulated “forever chemicals” through dilution. PFAS and precursors deposit with SSA on the dune surface and are transported with infiltrating (rain)water into the groundwater. In the subsurface, PFAS precursors may degrade into persistent PFAS, thereby contributing to long-term PFAS contamination. This re-emission challenges European water utilities striving to comply with increasingly strict PFAS limits for drinking water from dune filtration systems. Numerical models serve as a useful tool to investigate PFAS behaviour in the subsurface by extending the insights from observations and providing a quantitative framework to predict, assess, and analyze contaminants. State-of-the-art PFAS models are restricted to firefighting sites or numerical experiments and lack field calibration, leaving a critical gap in understanding PFAS behaviour in dune sites. LINGERS breaks this barrier by, for the first time, explicitly modelling PFAS and precursor degradation to predict PFAS concentrations at the Haamstede field site. Existing monitoring data from Haamstede will be analysed to trace how PFAS and precursors are transported from the dune surface through the unsaturated and saturated zones to the abstraction wells. These insights will inform a conceptual model that guides the extension of an existing 2D MODFLOW6 model of the saturated zone with USGT-PFAS, enabling simulation of the coupled flow and reactive transport of PFAS and precursors at any field site. The 2D transferable modelling frameworks will be further developed into a Haamstede site-specific 3D model calibrated with field data to predict concentrations. By providing a modelling tool, LINGERS will support water utilities and decision-makers in safeguarding drinking water supplies across Europe.