Characterization Report for the 92-Acre Area of the Area 5 Radioactive Waste Management Site, Nevada Test Site, Nevada

Abstract

Office (NNSA/NSO) manages two low-level Radioactive Waste Management Sites (RWMSs) at the Nevada Test Site (NTS). The Area 5 RWMS uses engineered shallow-land burial cells to dispose of packaged waste. This report summarizes characterization and monitoring work pertinent to the 92-Acre Area in the southeast part of the Area 5 RWMS. The southeast quadrant covers 37 hectare (ha) (92 acres [ac]), and is referred to as the "92-Acre Area."The cells in the 92-Acre Area include 13 boreholes, 16 narrow trenches, and 9 broader pits. The waste disposal units were gradually established during 45 years of waste operations. Only three disposal units within the 92-Acre Area are currently active. Most of the disposal units have been operationally closed with covers of at least 2.4 meters (m) (8 feet [ft]) of native fill. Closure of the 92-Acre Area disposal units is anticipated by 2011.Current closure plans organize the disposal cells of the 92-Acre Area into six closure units by physical location, waste types, and regulatory requirements. One of these closure units is Federal Facility Agreement and Consent Order Corrective Action Unit (CAU) 111: Retired Mixed Waste Pits. The CAU 111 pits and trenches were operated prior to the promulgation of the Resource Conservation and Recovery Act (RCRA) and may have received both low-level waste (LLW) and low-level mixed waste (LLMW). A proposed single final closure cover and a monitoring plan will meet the needs of all six closure units within the 92-Acre Area. Studies indicate a monolayer soil cover will provide the equivalent protection of a standard RCRA cover, and offer superior performance with respect to subsidence.The precursor to the Area 5 RWMS, the Sugar Bunker Dump, began receiving waste by 1960 and began burying waste in January 1961. The Area 5 RWMS was established in 1978 on a 296 ha (732-ac) site incorporating the existing Sugar Bunker Dump waste cells in the southeast corner. The thirteen 37-m (120-ft) boreholes were drilled in the 1980s for the Greater Confinement Disposal (GCD) program. The GCD program was terminated before all the boreholes were used.Both classified and unclassified materials are managed at this facility. Unclassified disposal records and historic records indicate waste types in the 92-Acre Area include LLW, LLMW, asbestiform waste, transuranic (TRU) waste, and mixed TRU waste. Most of the inventory is LLW, and much of the LLW contains radionuclides that will decay significantly over the next several decades. Most of the TRU and potential mixed TRU waste is in boreholes over 21 m (70 ft) below ground surface. Thorium waste is present in the lowest tier of one disposal pit. Two disposal units have been designated for asbestos waste. Much of the suspected LLMW was deposited at the oldest disposal units prior to the promulgation of RCRA. The contaminants are not readily released or transported, due to the structure (such as lead shielding). The waste acceptance criteria, packaging requirements, monitoring, and other factors in the operation of the interi...