Characterization of the PFAS-Contaminated Fractured Rock Aquifer (FRA) Beneath the Rutland-Southern Vermont Regional Airport (RSVRA)  

Jonathan Kim, PhD

State Geologist, Vermont Geological Survey

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Abstract: In 2018, many wells and springs near/at the Rutland Airport were found by the Vermont DEC to be contaminated with PFAS. The PFAS point sources are areas where aqueous film-forming foam (AFFF) was used to conduct annual equipment testing and to extinguish aircraft fires. The Vermont Geological Survey and partners used an aquifer characterization approach that integrated physical (geologic mapping, GIS analysis of well driller reports and geophysical logging) and chemical (PFAS, major and trace elements, stable isotopes, and recharge-ages) components to build a robust 3D conceptual site model (CSM) for understanding groundwater flow and contaminant transport in the study area. Bedrock geologic mapping was combined with photogrammetric analysis of structures observed in ground and drone photo mosaics of outcrops in the Clarendon Gorge. The structural chronology (oldest to youngest) is 1) isoclinal fold set and cleavage, 2) superposed anticline and syncline, 3) a third fold set that interferes with the second fold set and forms a dome and basin pattern, and 4) fracture zones with igneous intrusions. Geophysical logging of selected wells was used to map subsurface bedrock structures and lithologies in areas with limited outcrops. Contour maps of the bedrock surface show an irregular pattern of hills and valleys beneath the surficial deposits, which may influence groundwater flow. Piper diagrams, 2H/H vs. 18O/16O stable isotope plots, and average recharge-ages (tritium and CFCs), and PFAS species have proven useful for discriminating groundwater geochemical groups that reflect water-rock interaction. Low alkalinity, PFAS-free, “old” groundwater (> 50-year average recharge-age) was likely recharged into Cambrian quartzites on the west flank of the Green Mountains, traveling along flow paths to the fractured rock aquifer beneath the Rutland Airport. Our CSM suggests that groundwater and PFAS transport in the subsurface are influenced by a fractured, refolded, anticline – syncline pair