Framework for a Risk-Informed Groundwater Compliance Strategy for Corrective Action Unit 98: Frenchman Flat, Nevada National Security Site, Nye County, Nevada, Revision 1

Abstract

Note: This document was prepared before the NTS was renamed the Nevada National Security Site (August 23, 2010); thus, all references to the site herein remain NTS. Corrective Action Unit (CAU) 98, Frenchman Flat, at the Nevada Test Site (NTS) was the location of ten underground nuclear tests between 1965 and 1971. As a result, radionuclides were released in the subsurface in the vicinity of the test cavities. Corrective Action Unit 98 and other CAUs at the NTS and offsite locations are being investigated. The Frenchman Flat CAU is one of five Underground Test Area (UGTA) CAUs at the NTS that are being evaluated as potential sources of local or regional impact to groundwater resources. For UGTA sites, including Frenchman Flat, contamination in and around the test cavities will not be remediated because it is technologically infeasible due to the depth of the test cavities (150 to 2,000 feet [ft] below ground surface) and the volume of contaminated groundwater at widely dispersed locations on the NTS. Instead, the compliance strategy for these sites is to model contaminant flow and transport, estimate the maximum spatial extent and volume of contaminated groundwater (over a period of 1,000 years), maintain institutional controls, and restrict access to potentially contaminated groundwater at areas where contaminants could migrate beyond the NTS boundaries.