OCCURRENCE OF PER- AND POLYFLUOROALKYL SUBSTANCES (PFAS) IN SHALLOW GROUNDWATER BENEATH SOILS WITH LOW PFAS CONCENTRATIONS IN NEW HAMPSHIRE

Between 2020 – 2021, the U.S. Geological Survey (USGS) in collaboration with the New Hampshire Department of Environmental Services (NHDES) performed a statewide study focused on the occurrence of per- and polyfluoroalkyl substances (PFAS) in shallow soil at locations not known to be impacted by local releases of PFAS. Sample locations (n = 100) were randomized through an equal-area grid approach, and targeted undisturbed areas. At all locations, soil was collected from 0 – 6 inches (in) below ground surface (bgs). Results showed that PFAS compounds were detected at all 100 sample locations at varying concentrations [0.41 – 21 nanograms per gram (ng g^-1 ) ∑₃₆ PFAS]. This prompted an additional study to evaluate whether PFAS leaching from soils with relatively low PFAS concentrations results in groundwater PFAS concentrations of concern, given the widespread detections of PFAS in soil across the state of NH. Five of the original locations were re-sampled for soil at the 0 – 6 in bgs interval, as well as groundwater at varying depths (1.10 – 3.36 feet bgs). At one site, two lysimeters were installed to monitor PFAS concentrations as water infiltrated through the vadose zone. Soil analyses included pH, total organic carbon (TOC), and 40 PFAS compounds, and groundwater samples were analyzed for 40 PFAS compounds and in-situ physicochemical parameters. Analytical results showed that PFAS compounds in soil were similar to the statewide study (0.83 – 5.7 ng g^-1 ∑₄₀ PFAS). During two separate sampling events, concentrations of PFAS in groundwater ranged 5.2 – 42 ng L^-1 ∑₄₀ PFAS at three of the sites, and porewater collected from lysimeters contained PFAS at 9.4 – 120 ng L^-1 ∑₄₀ PFAS. Two of the sites had no detectable PFAS in groundwater. Results indicate that additional study may help to better understand how shallow groundwater is affected by PFAS loaded through infiltration processes.