This Corrective Action Decision Document identifies and rationalizes the U.S. Department of Energy, Nevada Operations Office's selection of a recommended corrective action alternative (CAA) appropriate to facilitate the closure of Corrective Action Unit (CAU) 407, Roller Coaster RADSAFE Area (RCRSA), under the Federal Facility Agreement and Consent Order. Located on Tonopah Test Range (TTR), CAU 407 is located approximately 140 miles northwest of Las Vegas, Nevada, and five miles south of Area 3. The RCRSA was used during May and June of 1963 to decontaminate vehicles, equipment, and personnel from the Clean Slate tests. As a result of these operations, the surface and subsurface soils in the area have been impacted by plutonium and other contaminants of potential concern associated with decontamination activities. In June and July 1998, corrective action investigation activities were performed at CAU 407 (as outlined in the related Corrective Action Investigation Plan [CAIP]). The purpose of this investigation was to determine if any analytes were present at the site in concentrations above the preliminary action levels (PALs). The results indicated in the detection of plutonium above the PAL in samples taken from surface and subsurface soil within the exclusion zone, and uranium and americium detected above the PAL in samples taken from surface soil within the exclusion zone. No other COCs were identified above PALs specified in the CAIP. Based on this data, two corrective action objectives (CAOs) were defined: (1) to prevent or mitigate human exposure to surface and subsurface soil containing COCs, and (2) to prevent adverse impacts to groundwater quality. To accomplish these objectives, five CAAs were developed and evaluated. Based on the results of the detailed and comparative analysis of these alternatives, Alternative 3 (Partial Excavation, Disposal, and Administrative Controls With a Surface Cap) was chosen as the preferred alternative. This alternative was judged to meet all requirements for the technical components evaluated, the applicable state and federal regulations for closure of the site, the CAOs under DOE Order 5400.5 and 10 Code of Federal Regulations 20, and the reduction of potential future exposure pathways to subsurface contaminated soil.
