Corrective Action Decision Document/Closure Report for Corrective Action Unit 482: Area 15 U15a/e Muckpiles and Ponds Nevada Test Site

This Corrective Action Decision Document /Closure Report (CADD/CR) was prepared by the Defense Threat Reduction Agency (DTRA) for Corrective Action Unit (CAU) 482 U15a/e Muckpiles and Ponds. This CADD/CR is consistent with the requirements of the Federal Facility Agreement and Consent Order agreed to by the State of Nevada, the U.S. Department of Energy, and the U.S. Department of Defense. Corrective Action Unit 482 is comprised of three Corrective Action Sites (CASs) and one adjacent area: CAS 15-06-01, U15e Muckpile; CAS 15-06-02, U15a Muckpile; CAS 15-38-01, Area 15 U15a/e Ponds; and Drainage below the U15a Muckpile. The purpose of this CADD/CR is to provide justification and documentation supporting the recommendation for closure with no further corrective action, by placing use restrictions on the three CASs and the adjacent area of CAU 482. To support this recommendation, a corrective action investigation (CAI) was performed in September 2002. The purpose of the CAI was to fulfill the following data needs as defined during the Data Quality Objective (DQO) process: (1) Determine whether contaminants of concern (COCs) are present. (2) If COCs are present, determine their nature and extent. (3) Provide sufficient information and data to determine appropriate corrective actions. The CAU 482 dataset from the CAI was evaluated based on the data quality indicator parameters. This evaluation demonstrated the quality and acceptability of the dataset for use in fulfilling the DQO data needs. Analytes detected during the CAI were evaluated against final action levels (FALs) established in this document. Tier 2 FALS were determined for the hazardous constituents of total petroleum hydrocarbons (TPH)-diesel-range organics (DRO) and the radionuclides americium (Am)-241, cesium (Cs)-137, plutonium (Pu)-238, and Pu-239. The Tier 2 FALs were calculated for the radionuclides using site-specific information. The hazardous constituents of TPH-DRO were compared to the PALs defined in the CAIP, and because none of the preliminary action levels (PALs) were exceeded, the PALs became the FALs. The radionuclide FALs were calculated using the Residual Radioactive (RESRAD) code (version 6.21). The RESRAD calculation determined the activities of all radionuclides that together would sum to an exposure dose of 25 millirem per year to a site receptor (based on their relative abundances at each CAS). Based on the field investigation, the following contaminants were determined to be present at concentrations exceeding their corresponding FALs: (1) CAS 15-06-01 - None. (2) CAS 15-06-02 - Cs-137 and Pu-239. (3) CAS 15-38-01 - Am-241, Cs-137, Pu-238, and Pu-239. (4) Drainage below CAS 15-06-02 - Cs-137 and Pu-239. Based on the data and risk evaluations, the DQO data needs presented in the Corrective Action Investigation Plan were met, and the data accurately represent the radiological and chemical risk present at CAU 482. Based on the results of the CAI data evaluation, it was determined that closure in place with use restrictions is the appropriate corrective action for CAU 482 and that use restrictions will effectively control exposure to future land users. This is based on the fact that even though the FALs were exceeded in a few samples, this remote, controlled access site poses only limited risk overall to public health and the environment. Given the relatively low levels of contamination present, it would create a greater hazard to worker safety, public health, and the environment to remove the contamination, transport it, and bury it at another location. Therefore, DTRA provides the following recommendations: (1) Close COCs in place at CAS 15-06-02, CAS 15-38-01, and the drainage below CAS 15-06-02 with use restrictions. (2) No further action for CAU 482. (3) A Notice of Completion be issued to DTRA by the Nevada Division of Environmental Protection for closure of CAU 482. (4) Move CAU 482 from Appendix III to Appendix IV of the Federal Facility Agreement and Consent Order