PHYSICAL CHARACTERIZATION OF THE PFAS-CONTAMINATED FRACTURED ROCK AQUIFER BENEATH THE RUTLAND- SOUTHERN VERMONT REGIONAL AIRPORT

Statewide testing for per- (and poly-) fluoroalkyl substance (PFAS) contamination of groundwater has been taking place since the 2016 discovery of PFAS contamination in the Town of Bennington. In 2018, numerous wells and springs near the Rutland-Southern Vermont Regional Airport (RSVRA) were found to be contaminated with PFAS. The primary PFAS sources are assumed to be from the use of Aqueous Fire-Fighting Foam (AFFF) during equipment tests and at 2 crash sites. Our research group integrates physical and chemical hydrogeological approaches to characterize PFAS-contaminated aquifers; the former consists of surficial and bedrock mapping (including UAV surveys), spatial analysis of well reports, and geophysical logging and the latter is comprised by analysis of groundwater for PFAS species, major and trace elements, stable isotopes, and recharge-ages. This report focuses on the physical approach.

To supplement bedrock mapping of the contamination area, detailed structural analysis along river gorges and state highways are underway. Along the lower and upper Clarendon gorges, UAV surveys have acquired multi-altitude imagery to assemble mosaics using photogrammetry software. Preliminary analysis of the imagery and field data shows well defined; steeply-dipping; N-S, E-W, and NE-SW -striking fracture zones, which may influence groundwater flow.

By correlating accurate well locations with well driller reports, preliminary maps were made in GIS of bedrock surface elevation, thickness of overlying unconsolidated sediment, and the potentiometric surface. The integration of structural data these maps indicates that fracture zones control surface water drainage and thickness of overburden.

Five bedrock wells in the RSVRA area, ranging in depth from 230-800’, were logged using borehole camera and temperature, conductivity, gamma, caliper, acoustic televiewer (AT), and heat-pulse flowmeter (HPF) tools. HPF measurements show upward flow from the bottom of all wells under ambient conditions. The attitudes of all planes intersecting the wells are being calculated from AT data.

The physical hydrogeological characterization forms a 3-dimensional framework to evaluate the chemical data sets, leading to an enhanced understanding of the fate and transport of PFAS.