Geohydrology of rocks penetrated by test well UE-25p#1, Yucca Mountain area, Nye County, Nevada

Test well UE-25pNo1 was drilled in cooperation with the U.S. Department of Energy in the southwestern part of the Nevada Test Site, for investigations related to the isolation of high-level nuclear wastes. Rocks penetrated in the well are predominantly ash-flow tuffs of Tertiary age to a depth of 1,244 meters and dolomite of Paleozoic age to a total depth of 1,805 meters. Hydraulic head is 20 meters higher in the Paleozoic dolomite than in most of the Tertiary tuffs; this hydraulic-head difference indicates a major hydrologic barrier to the downward movement of fluid. Any vertical fluid movement from the Tertiary to the Paleozoic sections would be small, as would be movement from the Paleozoic rocks into the Tertiary rocks. In the Tertiary section, an interval of less than 30 meters in the upper Prow Pass Member of Crater Flat Tuff has an apparent transmissivity of 14 meters squared per day. In the Paleozoic section, an interval of less than 22 meters has an apparent transmissivity of 69 meters squared per day. Compositions of water from the Tertiary and Paleozoic sections are similar to regional waters from rocks of the same ages. (USGS)