Final Characterization Report for Corrective Action Unit 109: Area 2 U-2BU Crater, Nevada Test Site, Nevada, Revision 1

Corrective Action Unit 109, Area 2 U-2bu Crater, is an inactive Resource Conservation and Recovery Act Part A Permit disposal unit located in Area 2 at the Nevada Test Site, Nevada. The Corrective Action Unit has been characterized under the requirements of the Nevada Test Site Resource Conservation and Recovery Act, Part A Permit (NDEP, 1995) and Title 40 Code of Federal Regulations Part 265 (CFR, 1996). The site characterization was performed under the RCRA Part A Permit Characterization Plan for the U-2bu Subsidence Crater (DOE/NV, 1998c), as approved by the Nevada Division of Environmental Protection (Liebendorfer, 1998). The primary objective of the site characterization activities was to evaluate the presence, concentration, and extent of any Resource Conservation and Recovery Act contaminants in the crater. Surface soil samples were collected on April 22, 1998, and subsurface soil samples and geotechnical samples were collected from April 27-29, 1998. Soil samples were collected using a hand auger or a piston-type drive hammer to advance a 5-centimeter (2-inch) diameter steel sampling tool into the ground. The permit for the Nevada Test Site requires that Corrective Action Unit 109 be closed under 40 Code of Federal Regulations 265 Subpart G and 40 Code of Federal Regulations Part 265.310 (CFR, 1996). Analysis of the data collected during the characterization effort indicates that lead was detected in Study Area 1 at 5.7 milligrams per liter, above the regulatory level in 40 Code of Federal Regulations 261.24 of 5.0 milligrams per liter. Except for the lead detection at a single location within the crater, the original Resource Conservation Recovery Act constituents of potential concern determined between the U.S. Department of Energy, Nevada Operations Office and the Nevada Department of Environmental Protection during the Data Quality Objectives process (DOE/NV, 1998b) were not found to be present at Corrective Action Unit 109 above regulatory levels of concern. The single lead detection that exceeded regulatory limits was discovered at a depth of 1.2 meters (4 feet) in Study Area 1. Total petroleum hydrocarbons were detected in Study Area 4 at two locations at concentrations of 130 and 190 milligrams per kilogram. These concentrations exceed the 100 milligram per kilogram action level established in Nevada Administrative Code 445A.2272 (NAC, 1996). The primary conceptual model identified during the Data Quality Objectives process appears to have been substantiated by the analytical results from site characterization; migration of contaminants of potential concern does not appear to be occurring, as none were detected in a significant percentage of the characterization samples. Based on the results of the characterization, clean closure by removal and disposal of impacted soil will be evaluated in the closure plan to address Study Area 1. An (a) through (k) analysis, as specified in Nevada Administrative Code 445A.227, should be used to evaluate total petroleum hydrocarbon contamination within Study Area 4. Study Areas 2, 3, and 5 should be clean closed without further assessment or remediation (see Figures 2-1 and 5-1 in the Characterization Report)