This Corrective Action Decision Document has been prepared for Corrective Action Unit (CAU) 145, Wells and Storage Holes in Area 3 of the Nevada Test Site, Nevada, in accordance with the ''Federal Facility Agreement and Consent Order'' (1996). Corrective Action Unit 145 is comprised of the following corrective action sites (CASs): (1) 03-20-01, Core Storage Holes; (2) 03-20-02, Decon Pad and Sump; (3) 03-20-04, Injection Wells; (4) 03-20-08, Injection Well; (5) 03-25-01, Oil Spills; and (6) 03-99-13, Drain and Injection Well. The purpose of this Corrective Action Decision Document is to identify and provide the rationale for the recommendation of a corrective action alternative for the six CASs within CAU 145. Corrective action investigation activities were performed from August 1, 2005, through November 8, 2005, as set forth in the CAU 145 Corrective Action Investigation Plan and Record of Technical Change No. 1. Analytes detected during the Corrective Action Investigation (CAI) were evaluated against appropriate final action levels to identify the contaminants of concern for each CAS. The results of the CAI identified contaminants of concern at one of the six CASs in CAU 145 and required the evaluation of corrective action alternatives. Assessment of the data generated from investigation activities conducted at CAU 145 revealed the following: CASs 03-20-01, 03-20-02, 03-20-04, 03-20-08, and 03-99-13 do not contain contamination; and CAS 03-25-01 has pentachlorophenol and arsenic contamination in the subsurface soils. Based on the evaluation of analytical data from the CAI, review of future and current operations at the six CASs, and the detailed and comparative analysis of the potential corrective action alternatives, the following corrective actions are recommended for CAU 145. No further action is the preferred corrective action for CASs 03-20-01, 03-20-02, 03-20-04, 03-20-08, and 03-99-13. Close in place is the preferred corrective action for CAS 03-25-01. The preferred corrective action alternatives were evaluated on technical merit focusing on performance, reliability, feasibility, safety, and cost. The alternatives were judged to meet all requirements for the technical components evaluated. The alternatives meet all applicable federal and state regulations for closure of the site and will reduce potential exposure pathways to the contaminated media to an acceptable level at CAU 145.
