Geology topics
Publications and source records attributed to R. K. Blankennagel.
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Yucca Mountain, Nevada, is one of several sites under consideration for construction of the first repository for high-level nuclear waste. The climate is arid; few perennial streams are present in the region. Flash floods occasionally occur. The site is underlain by at least 1,800 meters of volcanic tuffs of Tertiary age; limestones and dolomites of Paleozoic age underlie much of the surrounding region, and, together with alluvial deposits, comprise the major aquifers. Yucca Mountain is in the Alkali Flat-Furnace Creek Ranch ground-water subbasin, which is part of the Death Valley ground-water basin. Discharge occurs at Alkali Flat almost entirely by evapotranspiration, and at Furnace Creek Ranch from small springs and seeps. Beneath Yucca Mountain, depth to water ranges from about 460 to 700 meters; the rock under consideration for construction of the repository is in the unsaturated zone. Rate of recharge at Yucca Mountain is small, perhaps much less than 5 millimeters per year. Within the saturated zone, water movement is principally along fractures. The hydraulic gradient is small east (downgradient) of Yucca Mountain, and increases to the north and west. Lack of effective-porosity data presently precludes accurate calculation of flow velocity and travel times.
Ten wells in the Yucca Mountain area of southern Nevada have been sampled for chemical analysis. Samples were obtained during pumping of water from the entire well bore (composite sample) and in one instance by pumping water from a single isolated interval in well UE-25b number 1. Sodium is the most abundant cation and bicarbonate the most abundant anion in all water samples. Although the general chemical compositions of individual samples are similar, there are significant differences in uncorrected carbon-14 age and in inorganic and stable-isotope composition. Flow surveys of seven wells performed using iodine-131 as a tracer indicate that groundwater production is usually from one or more discrete zones of permeability. (Author 's abstract)
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This report describes the testing techniques used by the U. S. Geological Survey to obtain hydrologic data in deep holes drilled in volcanic rocks at Pahute Mesa, Nevada Test Site. The testing program in each hole includes geophysical logging, pumping, and injecting and swabbing between straddle packers. Rock lithologies and qualitative data on hydrologic conditions in the borehole are obtained from electric, caliper, temperature, and fluid resistivity logs. Quantitative data on major water-yielding intervals in the borehole are obtained from radioactive tracer and spinner surveys. Pumping tests are made to measure the combined yield of the various aquifers. Injection and swabbing tests are made by adding known volumes of water to, or withdrawing known volumes of water from, straddle-packed intervals and observing the rate of decline or rise in water level resulting from this injection or withdrawal of water. The yield of tested intervals is stated as relative specific capacity, in units of gallons per minute per foot of drawdown.