Potential Groundwater Recharge and the Effects of Soil Heterogeneity on Flow atTwo Radioactive Waste Management Sites at the Nevada Test Site

摘要

Two low-level Radioactive Waste Management Sites (RWMSs), consisting of shallowland burial disposal units at the Nevada Test Site (NTS), are managed by Bechtel Nevada for the U.S. Department of Energy, National Nuclear Security Administration. The NTS has an arid climate with annual average precipitation of about 17 cm at the Area 3 RWMS and about 13 cm at the Area 5 RWMS. The vadose zone is about 490 m thick at the Area 3 RWMS, and about 235 m thick at the Area 5 RWMS. Numerous studies indicate that under current climatic conditions, there is generally no groundwater recharge at these sites. Groundwater recharge may occur at isolated locations surrounding the RWMSs, such as in large drainage washes. However, groundwater recharge scenarios (and radionuclide transport) at the RWMSs are modeled in support of Performance Assessment (PA) documents required for operation of each RWMS. Recharge scenarios include conditions of massive subsidence and flooding, and recharge resulting from deep infiltration through bare-soil waste covers. This paper summarizes the groundwater recharge scenarios and travel time estimates that have been conducted in support of the PAs, and examines the effects of soil hydraulic property heterogeneity on flow.