Closure Report for the 92-Acre Area and Corrective Action Unit 111: Area 5 WMD Retired Mixed Waste Pits, Nevada National Security Site, Nevada

This Closure Report (CR) presents information supporting closure of the 92-Acre Area, which includes Corrective Action Unit (CAU) 111, 'Area 5 WMD Retired Mixed Waste Pits.' This CR provides documentation supporting the completed corrective actions and confirmation that the closure objectives were met. This CR complies with the requirements of the Federal Facility Agreement and Consent Order (FFACO) (FFACO, 1996 [as amended March 2010]). Closure activities began in January 2011 and were completed in January 2012. Closure activities were conducted according to Revision 1 of the Corrective Action Decision Document/Corrective Action Plan (CADD/CAP) for the 92-Acre Area and CAU 111 (U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office [NNSA/NSO], 2010). The following closure activities were performed: (1) Construct an engineered evapotranspiration cover over the boreholes, trenches, and pits in the 92-Acre Area; (2) Install use restriction (UR) warning signs, concrete monuments, and subsidence survey monuments; and (3) Establish vegetation on the covers. UR documentation is included as Appendix C of this report. The post-closure plan is presented in detail in Revision 1 of the CADD/CAP for the 92-Acre Area and CAU 111, and the requirements are summarized in Section 5.2 of this document. When the next request for modification of Resource Conservation and Recovery Act Permit NEV HW0101 is submitted to the Nevada Division of Environmental Protection (NDEP), the requirements for post-closure monitoring of the 92-Acre Area will be included. NNSA/NSO requests the following: (1) A Notice of Completion from NDEP to NNSA/NSO for closure of CAU 111; and (2) The transfer of CAU 111 from Appendix III to Appendix IV, Closed Corrective Action Units, of the FFACO