Intensely fractured Precambrian and Paleozoic carbonate and clastic rocks and block-faulted Cenozoic volcanic and sedimentary strata in the Nevada Test Site are divided into 10 hydrogeologic units. Three of these the lower clastic aquitard, the lower carbonate aquifer, and the tuff aquitard control the regional movement of ground water. The coefficients of fracture transmissibility of these rocks are, respectively, less than 1,000, 1,000 to 900,000, and less than 200 gallons per day per foot; interstitial permeability is negligible. Solution caverns are locally present in the carbonate aquifer, but regional movement of water is controlled by variations in fracture transmissibility and by structural juxtaposition of the aquifer and the lower clastic aquitard. Water circulates freely to depths of at least 1,500 feet beneath the top of the aquifer and up to 4,200 feet below land surface. Synthesis of hydrogeologic, hydrochemical, and isotopic data suggests that an area of at least 4,500 square miles (including 10 intermontane valleys) is hydraulically integrated into one groundwater basin, the Ash Meadows basin, by interbasin movement of ground water through the widespread carbonate aquifer. Discharge from this basin a minimum of about 17,000 acre-feet annually occurs along a fault-controlled spring line at Ash Meadows in east-central Amargosa Desert. Intrabasin movement of water between Cenozoic aquifers and the lower carbonate aquifer is controlled by the tuff aquitard, the basal Cenozoic hydrogeologic unit. Such movement significantly influences the chemistry of water in the carbonate aquifer. Groundwater velocity through the tuff aquitard in Yucca Flat is less than 1 foot per year. Velocity through the lower carbonate aquifer ranges from an estimated 0.02 to 200 feet per day, depending upon geographic position within the flow system. Within the Nevada Test Site, ground water moves southward and southwestward toward Ash Meadows. C2 HYDROLOGY OF NUCLEAR TEST SITES The scope of the report is broad in view of the complexities of the geology, the vastness of the study area, and the absence of previous detailed hydrogeologic studies of similar terrane. Yet, the types and quantity of data obtained during this investigation are seldom available in hydrogeologic studies. In addition to standard hydrologic data, a wealth of geologic, geophysical, geochemical, and isotopic data were used to supplement interpretations of the hydrologic data. To a first approximation, therefore, the objectives of the study are believed to have been accomplished. The development of groundwater supplies was an important byproduct of the investigation; more than half the test holes are used as water wells. This report does not discuss the exploration for, and development of, new water supplies, although many of the data and interpretations will aid others in such tasks.

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Regional interbasin movement of ground water in highly deformed miogeosynclinal carbonate rocks of the eastern Great Basin has received considerable attention in the literature since 1960. That these regional carbonate aquifer systems -some of which may integrate as many as 13 intermontane basinsare actually compartmentalized by major structural features, has not received adequate emphasis.In south-central Nevada, major wrench, thrust, and normal faults and folds exert marked control on ground-water movement. Deformation of the carbonate rocks results in regions of high transmissibility, but juxtaposition by faulting or folding of thick clastic strata against carbonate aquifiers results in prominent ground-water barriers, some of which are more than ten miles long. The apparent hydraulic gradients across the thick clastic aquitards vary from 150 to 1300 ft per mile; by contrast gradients in the adjacent carbonate aquifers vary from 0.5 to 10 ft per mile. Barriers may also result from gouge developed along the major fault zones.Recognition of the structural barriers as well as the conduits is essential for construction of an initial working flow net of a region. In upland areas 35 on June 4, 2015 memoirs.gsapubs.org Downloaded from 36 NEVADA TEST SITE the clastic aquitards may exert control on distribution of recharge. Where present in central parts of the flow system, the aquitards act as prominent ground-water dams, and localize minor spring discharge. In discharge areas they localize major spring lines.Major structures with hydrologic reflections include the Las Vegas Valley shear zone and the Tippinip thrust fault. CONTENTS

This report presents data collected to determine the hydraulic characteristics of rocks penetrated in test well USW H-l. The well is one of a series of test wells drilled in and near the southwestern part of the Nevada Test Site, Nye County, Nevada, in a program conducted on behalf of the U.S. Department of Energy. These investigations are part of the Nevada Nuclear Waste Storage Investigations to identify suitable sites .for storage of high-level radioactive wastes. Data on drilling operations, lithology, borehole geophysics, hydrologic monitoring, core analysis, groundwater chemistry and pumping and injection tests for well USW H-l are contained in this report.