Corrective Action Investigation Plan for the CNTA Subsurface Sites (CAU Number 443), Revision 1; FINAL

This Corrective Action Investigation Plan (CAIP) describes the U.S. Department of Energy's (DOE's) planned environmental investigation of the subsurface Central Nevada Test Area (CNTA) Corrective Action Unit (CAU) No. 443. The CNTA is located in Hot Creek Valley in Nye County, Nevada, adjacent to U.S. Highway 6, about 48 kilometers (km) (30 miles[mi]) north of Warm Springs, Nevada. The CNTA was the site of Project Faultless, a nuclear device detonated in the subsurface by the U.S. Atomic Energy Commission (AEC) in January 1968. The purposes of this test were to gauge the seismic effects of a relatively large, high-yield detonation completed in Hot Creek Valley (outside the Nevada Test Site) and to determine the suitability of the site for future large detonations. The yield of the Faultless test was between 200 kilotons and 1 megaton. Two similar tests were planned for the CNTA, but neither of them was completed. Based on the general definition of a corrective action investigation (CAI) from Section IV.14 of the Federal Facility Agreement and Consent Order (FFACO), the purpose of the CAI is ''to gather data sufficient to characterize the nature, extent, and rate of migration or potential rate of migration from releases or discharges of pollutants or contaminants and/or potential releases or discharges from corrective action units identified at the facilities''. For CNTA CAU 443 the concepts developed for the Underground Test Area (UGTA) CAUs will be applied on a limited scale. For the UGTA CAUs, ''the objective of the CAI process is to define boundaries around each UGTA CAU that establish areas that contain water that may be unsafe for domestic and municipal use,'' as stated in Appendix VI of the FFACO (1996). Based on this strategy the CAI for CAU 443 will start with modeling using existing data. New data collection activities are generally contingent upon the results of the modeling and may or may not be part of the CAI. Specific objectives of the CAI ar e as follows: (1) determine the characteristics of the groundwater flow system, the sources of contamination, and the transport processes to acceptable levels of uncertainty; (2) develop a credible numerical model of groundwater flow and contaminant transport for the UC-1 Subsurface Corrective Action Site (CAS) and downgradient areas; and, (3) develop stochastic predictions of the contaminant boundary at an acceptable level of uncertainty