TRACING INFILTRATION OF PFAS CONTAMINATION FROM SOIL TO A FRACTURED BEDROCK AQUIFER USING TRACE ELEMENT AND ISOTOPE GEOCHEMISTRY

Widespread PFAS groundwater contamination in Hoosick Falls, NY and Bennington, VT has impacted over 1,000 wells across a >100 square mile area (250 km²). Most of these residential wells and the Hoosick Falls village water supply are contaminated with PFOA above the EPA’s health advisory level. Contamination of the groundwater comes mainly from deposition to the land surface of PFOA aerosols emitted from manufacturers, PFOA is then transmitted through the vadose zone to contaminate both unconsolidated and bedrock aquifers. However, PFOA concentrations across the area are highly variable, and some wells contain anomalously low concentrations despite being within the boundaries of the contaminant plume. We report here on efforts to understand the transmission of aerosol-deposited PFOA from glacial till and fluvial aquifers to the fractured rock aquifer through multi-component analysis of geochemical and stable isotope data. We have compiled a dataset that includes water samples from private bedrock wells, overburden monitoring wells and shallow borings, springs, and groundwater seeps. Principal Component Analysis was used in attempt to differentiate distinct aquifer recharge sources. Groundwater samples were grouped by inferred recharge sources, followed by a statistical analysis to determine a relationship with average PFOA concentrations and recharge patterns in overburden wells. Initial results suggest a relationship between high PFOA concentrations and slower, lower-permeability flow paths through the unconsolidated aquifer, suggesting that dilution by meteoric water along higher-permeability flow paths may be an important factor in controlling PFOA concentrations. Additionally, portions of the fractured rock aquifer that receive recharge directly from the overlying unconsolidated materials generally have higher PFOA concentrations than parts of the aquifer that receive recharge from more distant flow paths.