SPATIAL AND TEMPORAL VARIATIONS IN SHALLOW GROUNDWATER PFOA CONTAMINATION IN BENNINGTON, VT: MATRIX DIFFUSION OF PFAS DURING INFILTRATION THROUGH HETEROGENEOUS TILL

Extensive perfluorooctanoic acid (PFOA) groundwater contamination from Teflon manufacturing in the Bennington, VT/Hoosick Falls, NY area has impacted over 1,000 residential wells and a municipal water supply. We present results and interpretation from three years of shallow monitoring well observation in the center of the regional PFOA plume. Seven wells were completed to similar depths within a sandy till formation in areas directly downwind of a factory that emitted PFOA aerosols from 1978 to 2002. While the degree of PFOA contamination is highly spatially variable, it has been temporally very stable. Wells less than 100 m from one another have average PFOA concentration ranging from 180 ppt to 2,400 ppt. These contamination levels have been stable for three years of monitoring. Continuous logging of water level and temperature in the wells indicates that permeability and connection to surface recharge are the primary factors controlling PFOA concentration. Wells with lower average PFOA concentrations have larger seasonal temperature variation, shorter lag response to seasonal temperature changes, and greater responses to precipitation than wells with higher concentrations. This pattern of higher PFOA concentration in wells surrounded by lower permeability materials is consistent with back-diffusion of PFOA from fine-grained lenses within the till, suggesting that matrix-diffusion is an important consideration in PFOA fate and transport. Given the stability of contamination levels during the three-year monitoring period, which began 15 years after the cessation of local manufacturing, it is likely that PFOA in shallow groundwater will continue to contribute to surface water contamination and contamination in the deeper fractured-rock aquifer for many decades to come.