Borehole and geohydrologic data for test hole USW UZ-6, Yucca Mountain area, Nye County, Nevada

Abstract

Test hole USW UZ-6, located 1. 8 kilometers west of the Nevada Test Site on a major north-trending ridge at Yucca Mountain, was dry drilled in Tertiary tuff to a depth of 575 meters. The area near this site is being considered by the U.S. Department of Energy for potential construction of a high-level, radioactive-waste repository. completed in the unsaturated zone as part of the U.S. Geological Survey's Yucca Mountain Project to characterize the potential repository site. pertaining to borehole drilling and construction, lithology of geologic units penetrated, and laboratory analyses for hydrologic characteristics of samples of drill-bit cuttings are included in this report. Test hole USW UZ-6 is one of seven test holes Data Test hole USW UZ-6 penetrated an estimated 77 percent of the unsaturated zone present at the drilling site. encountered while drilling. selected intervals for determining lithology, water content, and water potential of the geologic units penetrated. No saturated perched water zones were Samples of drill-bit cuttings were collected at The water content in the samples collected is related to the degree of welding of the rock units; densely welded tuff is relatively dry; nonwelded and bedded tuff is relatively moist. Average values of gravimetric water content for the driest zones of the densely welded sections of the Miocene Tiva Canyon Member and the Topopah Spring Member of the Paintbrush Tuff were 0.024 and 0.020 gram per gram, respectively; the average values of water potential were-7,500 and-16,000 kilopascals, respectively. Average values of gravimetric water content for the nonwelded tuff of the Tiva Canyon Member and the bedded tuff unit of the Paintbrush Tuff were 0.107 and 0.121 gram per gram, respectively; average values of water potential were-270 and-74 kilopascals, respectively.