Few hydrogeological studies have focused on possible per- and poly-fluoroalkyl substance (PFAS) contamination in groundwater with particular attention to the role of hydraulic interconnections and to the interdigitations present between shallow and deep aquifer layers in heterogeneous alluvial systems. In general, deeper groundwater is considered chemically safer and less impacted by contamination, especially in multilayer aquifers characterized by low permeability apparently confining horizons. Therefore, this research analyzed PFAS in groundwater at depths ranging from 20 to 120 m below ground level, combining stratigraphic, hydrogeological, and chemical data with GIS mapping to identify industrial activities potentially contributing to PFAS contamination using the cross-checking methodology. During the second survey, the monitoring network was extended along a hydrogeological transect, including two springs located upstream and downstream of the deep wells, to assess PFAS concentration in shallow groundwater and the possible transfer along the groundwater flow path. The intra-site comparative analysis reveals, for the same sampling locations, a differentiation in the PFAS profiles detected across the two monitoring campaigns, indicating a temporal evolution in the chemical composition. Furthermore, chemical results show the presence of PFAS exclusively in deep monitoring wells, confirming a spatially heterogeneous distribution within the aquifer system. These results highlight both the temporal and spatial evolution of PFAS concentration, suggesting a complex contaminant migration pathway along preferential gravel and sand horizons in deeper aquifer layers. The conceptual hydrogeological model confirmed hydraulic interconnections among aquifer layers and identified zones of higher vulnerability to contamination. The analysis of possible PFAS migration pathways at the basin scale raised some questions about the influence of wells features and management practices on PFAS distribution in shallow and deep groundwater. The findings of this research contribute to environmental sustainability, providing initial insights for measuring and managing the presence and pathways of PFAS in deep alluvial aquifers.
Ducci et al. (Sat,) studied this question.