The geologic and hydrogeologic setting of the Waste Isolation Pilot Plant

The Waste isolation Pilot Plant (WIPP) is a mined repository for the perman ent disposal of transuranic wastes. It has been constructed by the United S tates Department of Energy (DOE) in semiarid, sparsely inhabited rangeland in southeastern New Mexico. The disposal area is 655 m below the land surfa ce, in bedded salt of the Late Permian (approximately 255 million-years-old ) Salado Formation. The extremely low permeability of the halite and other evaporite rocks provide the primary geologic barrier assuring long-term (10 ,000-year-plus) isolation of the radioactive waste from the accessible envi ronment. Extensive geologic investigations during site characterization hav e provided information on the stratigraphy, structure, and natural resource s of the region (including hydrocarbons, potash, and groundwater), and have investigated the potential fur disruption by processes such as dissolution , salt deformation, tectonic activity, and climate change. Hydrogeologic in vestigations have documented the physical properties of the evaporite rocks , and have identified the Culebra Dolomite Member of the overlying Rustler Formation as the most transmissive water-bearing unit in the region. Lf the evaporite barriers are breached by accidental drilling intrusion, the Cule bra would provide the most likely pathway fur radionuclide transport away f rom the site. Although water in the Culebra is of poor quality and none is currently used for human consumption, groundwater flow and potential radion uclide transport in the unit have been studied in detail. Results of geolog ic and hydrogeologic studies of the WIPP region indicate that the geologic and hydro- geologic features of the site will provide effective long-term c ontainment of radionuclides. Geologic and hydrogeologic information is used in the performance assessment that supported the DOE's compliance certific ation application to the United States Environmental Protection Agency. Pub lished by Elsevier Science Ltd.