JUSTIFICATION FOR AN ALTERNATIVE LANDFILL DESIGN FOR THE MIXED WASTE DISPOSAL UNIT AT THE AREA 5 RADIOACTIVE WASTE MANAGEMENT SITE, NEVADA TEST SITE

摘要

The Pit 3 Mixed Waste Disposal Unit is located in Frenchman Flat within the Area 5 Radioactive Waste Management Site on the Nevada Test Site. The unit disposes on-site generated mixed waste from environmental cleanup activities. The Nevada Site Office is applying for a permit to bury off-site mixed waste and one component of the application is a cost-effective alternative landfill design. This design uses a defense-in-depth systems approach consisting of combined acceptance, operation and disposal practices, a vegetated, monolithic evapotranspiration closure cover, and lateral and lower buffer zones of native alluvial soil that enhance the natural protection provided by the arid climate setting and deep groundwater. The waste zone is located in a region of predominantly upward flow of liquid and vapor water more than 200 meters above the water table. These hydrologic features combined with the thick vegetated closure cover provide reasonable expectation of no drainage through the cover or the underlying waste zone. Verification of this conclusion is provided by decade long bare and vegetated lysimeter experiments, monitoring of operational covers, and numerical modeling of water and contaminant migration in the near surface disposal environment. Protection of the surface waters and groundwater during the operational phase will be provided by containzeration/encapsulation of waste, surface drainage features with a water collection trench, incremental coverage of waste by an operation cover and the highly evaporative conditions of the disposal setting. Limitations in requirements for application of evapotranspiration closure covers are not applicable to the Nevada Test Site setting and the Pit 3 disposal unit is a premier site for deployment of an alternative landfill design.