Hydrogeology of a Ground-Water Contamination Site, Cayuga County, New York

Problem - The U.S. Geological Survey (USGS) provided technical assistance between 2001 and 2013 to the U.S. Environmental Protection Agency (EPA) in an investigation of the presence of chlorinated solvents (trichloroethylene and degradates) in ground water in the Middle-to-Lower Devonian and Upper Silurian carbonate bedrock southwest of Auburn in Cayuga County, N.Y. Pieziometric and water-quality data from the wells indicate that contaminants may have migrated in the bedrock as far as 7 miles toward discharge areas that are in an adjacent surface-water basin. The ground-water contamination site was added to the Super Fund priority list in 2003.

Objectives - The objective of the work is to characterize the stratigraphy, fracture patterns, and water-bearing zones that are observed in boreholes as part of a regional appraisal of the contaminant distribution and the potential pathways of contaminant movement in the karst bedrock.

Approach - The EPA has installed 12 monitoring wells that tap multiple water-bearing zones in the carbonate-aquifer system, and the USGS has collected advanced borehole-geophysical logs in more than 60 wells to complement the conventional data program at the EPA wells. The geophysical data will be used to define the stratigraphy, lithology, and fractures penetrated by the wells, and flow zones under ambient open-hole conditions. The information has been used in a multiple-level monitoring design that isolates discrete pressure-head and water-quality monitoring zones between multiple packers within the wells. Since 2006, the USGS has been assisting in the installation and monitoring of an additional set of 11 multiple-level monitoring wells as EPA begins implementation of the Remedial Investigation at the site.

Benefits - Results of this study provide guidance to EPA for the design and implementation of additional monitoring and the potential remediation at the contamination site. The approach has applicability to other sites that have VOC contamination in fractured-rock and karst terrains in the humid regions of the United States.