BUILDING A 3-D CONCEPTUAL SITE MODEL FOR THE PFAS-CONTAMINATED FRACTURED ROCK AQUIFER BENEATH THE RUTLAND-SOUTHERN VERMONT REGIONAL AIRPORT (RSVRA)

In 2018, numerous wells and springs near the Rutland-Southern Vermont Regional Airport were found to be contaminated with PFAS by the Vermont Dept. of Environmental Conservation. The primary PFAS source is presumed to be the testing of Aqueous Film-Forming Foam (AFFF) equipment over decades and, secondly, the application of these chemicals at 2 plane crash sites. The Vermont Geological Survey and partners are characterizing the physical and chemical components of the fractured rock aquifer beneath the RSVRA to build a 3-D conceptual site model (CSM) that explains the “plumbing” of this aquifer. Here, we report on the integration of results from bedrock and surficial geologic mapping, the GIS analysis of well driller reports from groundwater wells, and the geophysical logging of selected wells.

Bedrock geologic mapping using conventional field techniques was coupled with the detailed photogrammetric analysis of structures observed in ground (including Gigapan^TM) and drone photo mosaics of continuous outcrop segments in/near the Clarendon Gorge. This work revealed the following relative structural chronology, which must be considered to assess groundwater and contaminant flow: 1) Intrastratal reclined isoclinal F₁ folds internal to dolomitic quartzite and rusty weathering calcareous phyllite beds (S₀) 2) A map-scale NNE-SSW trending, east-verging, asymmetric F₂ anticline and syncline pair with axial planar fracture cleavage intensified in the hinge zone; 3) Outcrop-scale NNE-SSW and E-W trending F₂ and F₃ orthogonal fold sets that form a dome and basin interference pattern, each with a fracture cleavage; 4) Alternating steeply-dipping ~E-W and N-S fracture zones, some of which contain lamprophyre intrusions.

The GIS analysis of groundwater wells in the RSVRA area documents that the bedrock surface is irregular and forms subsurface hills and valleys that likely influence groundwater flow. The surficial geologic and isopach maps show anomalously thick (>40’) deposits in the SE part of the airport that infill a bedrock basin. Geophysical logging was used to map subsurface bedrock structures and lithologies with gamma, caliper, acoustic televiewer, heat pulse flowmeter, and borehole camera tools. The completed 3-D CSM is being used to assess the movement of PFAS and associated groundwater chemical tracers.