Spatial and Temporal Variations in Shallow Groundwater Pfoa Contamination in Bennington, Vt: Matrix Diffusion of Pfas During Infiltration Through Heterogeneous Till

Schroeder, Timothy; CollegeScience, Bennington; Foley, Janet B.; Bond, David; Ging, Alexander; Hitzelberger, Michael; Nordyke, Alexandra; Salazar, E.; Watson, Benjamin

doi:10.1130/abs/2020am-357461

Cited by 1 publication

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“…Seven shallow monitoring wells, located between 400 m and 1,200 m from the ChemFab factory, were drilled in 2017 and 2018 after the discovery of PFOA in the area (Schroeder et al, 2020) (Figure 2). All well boring sites are between 30 m and 50 m in elevation above the ChemFab factory, have total depths ranging from 3.5 m to 6.7 m, and are screened at the shallow water table within glacial till.…”

Section: Surficial Monitoring Wellsmentioning

confidence: 99%

“…All well boring sites are between 30 m and 50 m in elevation above the ChemFab factory, have total depths ranging from 3.5 m to 6.7 m, and are screened at the shallow water table within glacial till. From multiple sampling events over 3 years, the average PFOA concentration in the wellwater ranges from 180 ppt to 2600 ppt (Schroeder et al, 2020). Three of these wells are drilled close to one another (80 m) near the top of Bingham Hill, ∼1 km northeast of ChemFab.…”

Section: Surficial Monitoring Wellsmentioning

confidence: 99%

“…Three of these wells are drilled close to one another (80 m) near the top of Bingham Hill, ∼1 km northeast of ChemFab. There is high spatial, but low temporal variability in PFOA levels between closely-spaced (80 m) wells located with screens that are set at the same depth horizons (Schroeder et al, 2020).…”

Section: Surficial Monitoring Wellsmentioning

confidence: 99%

“…Given that the elevations of the groundwater in these shallow wells are considerably above the ChemFab factory site, it is unlikely that PFOA contamination in groundwater migrated directly upward to these wells from this factory (Schroeder et al, 2020).…”

Section: Surficial Monitoring Wellsmentioning

confidence: 99%

“…The most reasonable explanation for the shallow groundwater contamination is that air-deposited PFOA from factory emissions was sequestered in soil, and is slowly leaching to infiltrating groundwater (Schroeder et al, 2020). This zone likely recharges the till and fractured rock aquifers and continually contributes legacy PFOA from soils and shallow surficial deposits to groundwater to this day (Schroeder et al, 2020).…”

Section: Surficial Monitoring Wellsmentioning

confidence: 99%

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Four-dimensional characterization of a PFOA-contaminated fractured rock aquifer (FRA) in Bennington, Vermont, U.S.A

et al. 2023

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Between 2016 and 2019, the Vermont Department of Environmental Conservation discovered that groundwater from over 50% (355/628) of wells and springs in the Bennington area had perfluorooctanoic acid (PFOA) concentrations > 20 parts/trillion (ppt) (Vermont action level). The distribution of contaminated wells was complex, with very different PFOA concentrations in closely-spaced wells (<100 m apart). PFOA was introduced into the environment by a factory that produced Teflon™-coated fabrics from about 1978–2002. Manufacturing involved PFOA expulsion from smokestacks followed by atmospheric transport, deposition, and downward leaching to the aquifer system. The fractured rock aquifer was characterized through physical components (geologic mapping, spatial analysis of wells, and geophysical logging) to build a Three-dimensional conceptual model and then map the spatial distribution of chemical groundwater tracers (PFOA, major and trace elements, stable isotopes, and and recharge ages), adding a fourth temporal dimension. The field area consists of four imbricated metamorphic rock slices bounded by thrust faults. The dominant fracture sets that overprint these slices control the N-S and E-W topographic “grain.” Geophysical logging divided wells into those completed internal to or on the margins of thrust slices. Major and trace element analysis shows that groundwater can be spatially discriminated into carbonate (TDS, Ca, Mg, HCO3), shaly (Sr, U, SO4), and siliceous (K, Si) groups. Depleted H2O stable isotope signatures characterize the siliceous group. Recharge-ages determined from CFC11, 12, and 113 and tritium correlate with geochemical groups and were divided into “older” (~1953–73) and “younger” (1963–88), which predate and are synchronous with factory operation, respectively. Our conceptual model shows recharge from highlands to the west and east flowing toward the Bennington valley where it is locally tapped by wells along thrust faults or fracture zones. This water has older recharge ages and anomalously low PFOA concentrations (<6.7 ppt in 12 of 15 samples, mean = 7.9 ppt) compared to the majority of wells in this region, which are completed in the internal portions of thrust slices. These wells contain groundwater with younger recharge ages and high PFOA concentrations (mean = 290 ppt) and occurrence (>20 ppt in 28/36 samples), indicating mixing of younger and older waters.

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Section: Surficial Monitoring Wellsmentioning

confidence: 99%

Section: Surficial Monitoring Wellsmentioning

confidence: 99%

Section: Surficial Monitoring Wellsmentioning

confidence: 99%

Section: Surficial Monitoring Wellsmentioning

confidence: 99%

Section: Surficial Monitoring Wellsmentioning

confidence: 99%

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