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At least 991 records · Page 55Linked to original sources
USGS1953

Preliminary reconnaissance survey for thorium, uranium, and rare-earth oxides, Bear Lodge Mountains, Crook County, Wyoming

An area about 6 miles north of Sundance, in the Bear Lodge Mountains, in Crook County, Wyo., was examined during August 1950 for thorium, uranium, and rare-earth oxides and samples were collected. Uranium is known to occur in fluorite veins and iron-manganese veins and in the igneous rocks of Tertiary age that compose the core of the Bear Lodge Mountains. The uranium content of the samples ranges from 0.001 to 0.015 percent in those from the fluorite veins, from 0.005 to 0.018 percent in those from the iron-manganese veins, and from 0.001 to 0.017 percent in those from the igneous rocks. The radioactivity of the samples is more than that expected from the uranium content. Thorium accounts for most of this discrepancy. The thorium oxide content of samples ranges from 0.07 to 0.25 percent in those from the iron-manganese veins and from 0.07 to 0.39 percent in those from the sedimentary rocks, and from0.04 to 0.30 in those from the igneous rocks. Rare-earth oxides occur in iron-manganese veins and in zones of altered igneous rocks. The veins contain from 0.16 to 12.99 percent rare-earth oxides, and the igneous rocks, except for two localities, contain from 0.01 to 0.42 percent rare-earth oxides. Inclusions of metamorphosed sedimentary rocks in the intrusive rocks contain from 0.07 to 2.01 percent rare-earth oxides.

Wyoming↗
USGS1953

Thorium investigations, 1950-52, Wet Mountains, Colorado

The Wet Mountain thorium district was discovered in 1950 by members of the U.S. Geological Survey during reconnaissance investigations for uranium made on the behalf of the Atomic Energy Commission The size of this new district is incompletely known, but the deposits found to date are in an area 20 miles long and about 10 miles wide, the southwest boundary of which extends northwest from Querida and Rosita Custer County, into Fremont County. Most of the deposits, however, are in the southeastern half of this area The thorium minerals occur in barite-sulfide veins along northwest-trending shear zones that cut a pre-Cambrian complex or amphibolite, biotite-granite gneiss, metagabbro, migmatite, microcline granites, pegmatite and white granite, and syenite (?) o Along the shear zones are premineralization basic (lamprophyre (?)) dikes. Thorite has been tentatively identified as the principal radio- active mineral It is associated with barite: quartz, galena, fluorite, limonite, and pyrite Some of the shear zones perhaps can be traced for as much as 2 miles, but the largest known thorium-bearing ore body is as much as 300 feet long, 26 feet wide, and 400 feet deep. Samples from the veins contain as much as 1.6 percent equivalent Th0 2 Eleven diamond drill holes, totaling 3,292.4 feet have explored five shear zones on the Haputa Ranch. Three ore bodies of possible economic interest are indicated in two interconnecting shear zones. No other deposits in the wet Mountains have been explored, or even sampled adequately to hazard an estimate as to grade and tonnage of reserves.

Colorado↗
USGS1954

Wet Mountains, Colorado, thorium investigations, 1952-1954

A 22-square mile tract (McKinley Mountain Area) of pre-Cambrian rocks and veins containing thorium was mapped at the scale of 1:6,000. This tract lies on the west flank of the Wet Mountains, Custer and Fremont Counties, northeast of Westcliffe, Colo. The bedrock is a complexly interlayered sequence of gneisses of metasedimetary origin, migmatite and granitic gneisses that have been transected by an albite syenite stock and numerous northwest-trending dikes, veins, and fractures. Hornblende-plagioclase and biotite-quartz-plagioclase gneisses are the principal metasedimentary rocks; pyroxene-scapolite, garnet, sillimanite, and quartzite zones are locally present. The most prominent rock is a poorly foliated, microcline, alaskitic granite gneiss which occurs as layers ranging from more than 500 feet in thickness down to migmatitic “lit-par-lit” type of injections less than an inch thick. Of less wide distribution, but of similar occurrence, are quartz monzonite and leuco-granodiorite gneisses. Although the foliation of the rocks generally is steep and trends northeast over most of the area, several northeast-trending folds have been mapped in the northern half of the area; a vertically plunging fold occurs in the southwest. The albite syenite is nonfoliated and is about 595 million years old (late pre-Cambrian) by the Larsen zircon method of age determination. Many of the dikes are related to the stock. More than 800 radioactive occurrences were found along the northwest-trending veins. Almost all the radioactivity is due to thorium which in its purest form occurs as a hydrated thorite-like mineral. The veins also contain carbonate minerals, barite, quartz, red and yellow iron oxides, and minor sulfides; no genetic relation of these minerals to the thorium has been established. Although most of the deposits are only weakly radioactive, richer concentrations are scattered as pockets and lenses along the veins.

Colorado↗
USGS1954

The stratigraphic and structural controls of the uranium deposits on Long Mountain, Fall River County, South Dakota

Numerous occurrences of uranium have been found in the Long Mountain area, Fall River County, S. Dak. Correlation diagrams prepared from drill, cores obtained from the U.S. Atomic Energy Commission indicate that the uranium is most abundant in two sandstone units, separated by mudstone in the Lakota sandstone of Early Cretaceous age. The lower uraniferous unit is composed of thick beds of very fine- to fine-grained sandstone with a few interfingering lentils of mudstone. The upper uraniferous unit is composed of interfingering beds of very fine-, fine-, and coarse-grained sandstone and mudstone. The uranium deposits on Long Mountain and in the area to the west are most numerous in a northeast-trending zone about a mile wide between two normal faults. The deposits between these faults are in two groups of different trend; the northern group has been incompletely explored. The sedimentary structures of the upper and lower mineralized sandstone between the faults have controlled the deposition of uranium and vanadium.

South Dakota↗
USGS1953

Uranium deposits at Shinarump Mesa and some adjacent areas in the Temple Mountain district, Emery County, Utah

Deposits of uraniferous hydrocarbons are associated with carnotite in the Shinarump conglomerate of Triassic age at Shinarump Mesa and adjacent areas of the Temple Mountain district in the San Rafael Swell of Emery County, Utah. The irregular ore bodies of carnotite-bearing sandstone are genetically related to lenticular uraniferous ore bodies containing disseminated asphaltitic and humic hydrocarbon in permeable sandstones and were localized indirectly by sedimentary controls. Nearly non-uraniferous bitumen commonly permeates the sandstones in the Shinarump conglomerate and the underlying Moekopi formation in the area. The ore deposits at Temple Mountain have been altered locally by hydrothermal solutions, and in other deposits throughout the area carnotite has been transported by ground and surface water. Uraniferous asphaltite is thought to be the non-volatile residue of an original weakly uraniferous crude oil that migrated into the San Rafael anticline; the ore metals concentrated in the asphaltite as the oil was devolatilized and polymerized. Carnotite is thought to have formed from the asphaltite by ground water leaching. It is concluded that additional study of the genesis of the asphaltitic uranium ores in the San Rafael Swell, of the processes by which the hydrocarbons interact and are modified (such as heat, polymerization, and hydrogenation under the influence of alpha-ray bombardment), of petroleum source beds, and of volcanic intrusive rocks of Tertiary age are of fundamental importance in the continuing study of the uranium deposits on the Colorado Plateau.

Utah↗
USGS1956

The physical behavior and geologic control of radon in mountain streams

Radon measurement were made in several small, turbulent mountain streams in the Wasatch Mountains near Salt Lake City and Ogden, Utah, to determine the relationship between the distribution of radon and its geologic environment. In this area, the distribution of radon in streams can be sued to locate points where relatively large amounts of radon-bearing ground water enter the stream, although other evidence of spring activity may be lacking. These points of influence ground water are marked by abrupt increases (as much as two orders of magnitude within a distance of 50 feet) in the radon content of the stream waters. The excess radon in the stream water is then rapidly lost to the atmosphere through stream turbulence. The rate of radon dissipation is an exponential function, of different slopes, with respect to distance of streamflow, and depend upon the rate and volume of streamflow, and the gradient and nature of the stream channel. The higher radon concentration can be generally related to specific stratigraphic horizons in several different drainage area. Thus, lithologic units which act as the primary aquifers can be identifies. In one area, thrust faults were found to control he influx of ground water into the stream. Estimates, based on radon concentration in stream and related spring waters, can also be made of the major increments of addition of ground water to streamflow where conventional methods such as stream gaging are not practical. The radon in the waters studied was found to be almost completely unsupported by radium in solution.

Utah↗
USGS2003

Explosive-residue compounds resulting from snow avalanche control in the Wasatch Mountains of Utah

A snow avalanche is a powerful force of nature that can play a significant role in developing mountain landscapes (Perla and Martinelli, 1975). More importantly, loss of life can occur when people are caught in the path of snow avalanches (Grossman, 1999). Increasing winter recreation, including skiing, snowboarding, snowmobiling, snowshoeing, and climbing in mountainous areas, has increased the likelihood of people encountering snow avalanches (fig. 1). Explosives are used by most ski areas and State highway departments throughout the Western United States to control the release of snow avalanches, thus minimizing the loss of human life during winter recreation and highway travel (fig. 2). Common explosives used for snow avalanche control include trinitrotoluene (TNT), pentaerythritoltetranitrate (PETN), cyclotrimethylenetrinitramine (RDX), tetrytol, ammonium nitrate, and nitroglycerin (Perla and Martinelli, 1975). During and after snowfall or wind loading of potential avalanche slopes, ski patrollers and Utah Department of Transportation personnel deliver explosive charges onto predetermined targets to artificially release snow avalanches, thereby rendering the slope safer for winter activities. Explosives can be thrown by hand onto target zones or shot from cannons for more remote delivery of explosive charges. Hand-delivered charges typically contain about 2 pounds of TNT or its equivalent (Perla and Martinelli, 1975). Depending on the size of the ski area, acreage of potential avalanche terrain, and weather conditions, the annual quantity of explosives used during a season of snow avalanche control can be substantial. For example, the three ski areas of Alta, Snowbird, and Brighton, plus the Utah Department of Transportation, may use as many as 11,200 hand charges per year (Wasatch Powderbird Guides, unpub. data, 1999) for snow avalanche control in Big and Little Cottonwood Canyons (fig. 3). If each charge is assumed to weigh 2 pounds, this equates to about 22,400 pounds of explosive hand charges per year. In addition, 2,240 to 3,160 Avalauncher rounds and 626 to 958 military artillery rounds (explosive mass not specified) are used each year by the three ski areas and the Utah Department of Transportation for snow avalanche control in Big and Little Cottonwood Canyons (Wasatch Powderbird Guides, unpub. data, 1999). The other ski area in Big Cottonwood Canyon, Brighton, uses about 2,000 pounds of explosives per year for snow avalanche control (Michele Weidner, Cirrus Ecological Solutions consultant, written commun., 2001).

Water-Resources Investigations Report↗
USGS2003

Hydrology and water-quality characteristics of Muddy Creek and Wolford Mountain Reservoir near Kremmling, Colorado, 1990 through 2001

A water-quality monitoring program was begun in March 1985 on Muddy Creek in anticipation of the construction of a reservoir water-storage project. Wolford Mountain Reservoir was constructed by the Colorado River Water Conservation District during 1992-94. The reservoir began to be filled in 1995. Water quality generally was good in Muddy Creek and Wolford Mountain Reservoir throughout the period of record (collectively, 1990 through 2001), with low concentrations of nutrients (median total nitrogen less than 0.6 and median total phosphorus less than 0.05 milligrams per liter) and trace elements (median dissolved copper less than 2, median dissolved lead less than 1, and median dissolved zinc less than 20 micrograms per liter). Specific conductance ranged from 99 to 1,720 microsiemens per centimeter. Cation compositions at Muddy Creek sites were mixed calcium-magnesium-sodium. Anion compositions were primarily bicarbonate and sulfate. Suspended-sediment concentrations ranged from less than 50 milligrams per liter during low-flow periods to hundreds of milligrams per liter during snowmelt. Turbidity in prereservoir Muddy Creek generally was measured at less than 10 nephelometric turbidity units during low-flow periods and ranged to more than 360 nephelometric turbidity units during snowmelt. Compared to prereservoir conditions, turbidity in Muddy Creek downstream from the reservoir was substantially reduced because the reservoir acted as a sediment trap. During most years, peak flows were slightly reduced by the reservoir or similar to peaks upstream from the reservoir. The upper first to fifteenth percentiles of flows were decreased by operation of the reservoir compared to prereservoir flows. Generally, the fifteenth to one-hundredth percentiles of flow were increased by operation of the reservoir outflow compared to prereservoir flows. Nutrient transport in the inflow is proportional to the amount of inflow-water discharge in a given year. Some nitrogen was stored in the water column and gain/loss patterns for total nitrogen were somewhat related to reservoir storage. Nitrogen tended to move through the reservoir, whereas phosphorus was mostly trapped within the reservoir in bottom sediments. The reservoir gained phosphorus every year (1996- 2001) and, as a percentage, more phosphorus was retained than nitrogen in years when both were retained in the reservoir due to stronger phosphorus tendencies for adsorption, coprecipitation, and settling. Only small amounts of phosphorus were available in the water column at the outflow, and reservoir water-column storage did not influence phosphorus outflowloading patterns as much as settling further upstream in the reservoir. From 1990 to 2001, upstream from the reservoir, concentrations and values of dissolved solids, turbidity, some major ions, and dissolved iron increased (p-value less than 0.10), and acid-neutralizing capacity decreased. From 1990 to 2001, there were no significant (p-value less than 0.10) trends in nutrient concentrations upstream from the reservoir. From 1990 to 2001, downstream from the reservoir, trends in concentrations and values of dissolved solids, turbidity, major ions, total ammonia plus organic nitrogen, dissolved and total-recoverable iron, and total-recoverable manganese were downward. Upstream and downstream water-quality constituents for the prereservoir (1990 to 1995) period were compared. Concentrations and values of dissolved solids, major ions, turbidity, and manganese were greater (p-value less than 0.10) at the downstream site. From 1995 to 2001 (postconstruction), upstream and downstream water-quality constituents also were compared. Concentrations of specific conductance and major ions increased at the downstream site when compared to the upstream site (p-value less than 0.10), except for acid-neutralizing capacity and silica, which decreased. Turbidity, concentrations of total-recoverable and dissolved manganese, and

Water-Resources Investigations Report↗
USGS2004

Secondary Mineral Deposits and Evidence of Past Seismicity and Heating of the Proposed Repository Horizon at Yucca Mountain, Nevada

The Drift Degradation Analysis (DDA) (BSC, 2003) for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada, describes model simulations of the effects of pre- and post-closure seismicity and waste-induced heating on emplacement drifts. Based on probabilistic seismic hazard analyses of the intensity and frequency of future seismic events in the region (CRWMS M&O, 1998), the DDA concludes that future seismicity will lead to substantial damage to emplacement drifts, particularly those in the lithophysal tuffs, where some simulations predict complete collapse of the drift walls. Secondary mineral studies conducted by the U.S. Geological Survey since 1995 indicate that secondary calcite and silica have been deposited in some fractures and lithophysal cavities in the unsaturated zone (UZ) at Yucca Mountain during at least the past 10 million years (m.y.), and probably since the tuffs cooled to less than 100?C. Tuff fragments, likely generated by past seismic activity, have commonly been incorporated into the secondary mineral depositional sequences. Preliminary observations indicate that seismic activity has generated few, if any, tuff fragments during the last 2 to 4 m.y., which may be inconsistent with the predictions of drift-wall collapse described in the DDA. Whether or not seismicity-induced tuff fragmentation occurring at centimeter to decimeter scales in the fracture and cavity openings relates directly to failure of tuff walls in the 5.5-m-diameter waste emplacement drifts, the deposits do provide a potential record of the spatial and temporal distribution of tuff fragments in the UZ. In addition, the preservation of weakly attached coatings and (or) delicate, upright blades of calcite in the secondary mineral deposits provides an upper limit for ground motion during the late stage of deposition that might be used as input to future DDA simulations. Finally, bleaching and alteration at a few of the secondary mineral sites indicate that they were subjected to heated gases at approximately the temperatures expected from waste emplacement. These deposits provide at least limited textural and mineralogic analogs for waste-induced, high-humidity thermal alteration of emplacement drift wall rocks.

Water-Resources Investigations Report↗
USGS2002

Results of Hydraulic Tests in Miocene Tuffaceous Rocks at the C-Hole Complex, 1995 to 1997, Yucca Mountain, Nye County, Nevada

Four hydraulic tests were conducted by the U.S. Geological Survey at the C-hole complex at Yucca Mountain, Nevada, between May 1995 and November 1997. These tests were conducted as part of ongoing investigations to determine the hydrologic and geologic suitability of Yucca Mountain as a potential site for permanent underground storage of high-level nuclear waste. The C-hole complex consists of three 900-meter-deep boreholes that are 30.4 to 76.6 meters apart. The C-holes are completed in fractured, variably welded tuffaceous rocks of Miocene age. Six hydrogeologic intervals occur within the saturated zone in these boreholes - the Calico Hills, Prow Pass, Upper Bullfrog, Lower Bullfrog, Upper Tram, and Lower Tram intervals. The Lower Bullfrog and Upper Tram intervals contributed about 90 percent of the flow during hydraulic tests. The four hydraulic tests conducted from 1995 to 1997 lasted 4 to 553 days. Discharge from the pumping well, UE-25 c #3, ranged from 8.49 to 22.5 liters per second in different tests. Two to seven observation wells, 30 to 3,526 meters from the pumping well, were used in different tests. Observation wells included UE-25 c #1, UE-25 c #2, UE-25 ONC-1, USW H-4, UE-25 WT #14, and UE-25 WT #3 in the tuffaceous rocks and UE-25 p #1 in Paleozoic carbonate rocks. In all hydraulic tests, drawdown in the pumping well was rapid and large (2.9-11 meters). Attributable mostly to frictional head loss and borehole-skin effects, this drawdown could not be used to analyze hydraulic properties. Drawdown and recovery in intervals of UE-25 c #1 and UE-25 c #2 and in other observation wells typically was less than 51 centimeters. These data were analyzed. Hydrogeologic intervals in the C-holes have layered heterogeneity related to faults and fracture zones. Transmissivity, hydraulic conductivity, and storativity generally increase downhole. Transmissivity ranges from 4 to 1,600 meters squared per day; hydraulic conductivity ranges from 0.1 to 50 meters per day; and storativity ranges from 0.00002 to 0.002. Transmissivity in the Miocene tuffaceous rocks decreases from 2,600 to 700 meters squared per day northwesterly across the 21-square-kilometer area affected by hydraulic tests at the C-hole complex. The average transmissivity of the tuffaceous rocks in this area, as determined from plots of drawdown in most or all observation wells as functions of time or distance from the pumping well, is 2,100 to 2,600 meters squared per day. Average storativity determined from these plot ranges is 0.0005 to 0.002. Hydraulic conductivity ranges from less than 2 to more than 10 meters per day; it is largest where prominent northerly trending faults are closely spaced or intersected by northwesterly trending faults. During hydraulic tests, the Miocene tuffaceous rocks functioned as a single aquifer. Drawdown occurred in all monitored intervals of the C-holes and other observation wells, regardless of the hydrogeologic interval being pumped. This hydraulic connection across geologic and lithostratigraphic contacts is believed to result from interconnected faults, fractures, and intervals with large matrix permeability. Samples of UE-25 c #3 water, analyzed from 1995 to 1997, seem to indicate that changes in the quality of the water pumped from that well are probably due solely to lateral variations in water quality within the tuffaceous rocks.

Water-Resources Investigations Report↗
USGS1984

Geohydrology of volcanic tuff penetrated by test well UE-25b#1, Yucca Mountain, Nye County, Nevada

Test well UE-25bNo1, located on the east side of Yucca Mountain in the southwestern part of the Nevada Test Site, was drilled to a total depth of 1,220 meters and hydraulically tested as part of a program to evaluate the suitability of Yucca Mountain as a nuclear-waste repository. The well penetrated almost 46 meters of alluvium and 1,174 meters of Tertiary volcanic tuffs. The composite hydraulic head for aquifers penetrated by the well was 728.9 meters above sea level (471.4 meters below land surface) with a slight decrease in loss of hydraulic head with depth. Average hydraulic conductivities for stratigraphic units determined from pumping tests, borehole-flow surveys, and packer-injection tests ranged from less than 0.001 meter per day for the Tram Member of the Crater Flat Tuff to 1.1 meters per day for the Bullfrog Member of the Crater Flat Tuff. The small values represented matrix permeability of unfractured rock; the large values probably resulted from fracture permeability. Chemical analyses indicated that the water is a soft sodium bicarbonate type, slightly alkaline, with large concentrations of dissolved silica and sulfate. Uncorrected carbon-14 age dates of the water were 14,100 and 13,400 years. (USGS)

Water-Resources Investigations Report↗
USGS1984

Finite-element simulation of ground-water flow in the vicinity of Yucca Mountain, Nevada-California

A finite-element model of the groundwater flow system in the vicinity of Yucca Mountain at the Nevada Test Site was developed using parameter estimation techniques. The model simulated steady-state ground-water flow occurring in tuffaceous, volcanic , and carbonate rocks, and alluvial aquifers. Hydraulic gradients in the modeled area range from 0.00001 for carbonate aquifers to 0.19 for barriers in tuffaceous rocks. Three model parameters were used in estimating transmissivity in six zones. Simulated hydraulic-head values range from about 1,200 m near Timber Mountain to about 300 m near Furnace Creek Ranch. Model residuals for simulated versus measured hydraulic heads range from -28.6 to 21.4 m; most are less than +/-7 m, indicating an acceptable representation of the hydrologic system by the model. Sensitivity analyses of the model 's flux boundary condition variables were performed to assess the effect of varying boundary fluxes on the calculation of estimated model transmissivities. Varying the flux variables representing discharge at Franklin Lake and Furnace Creek Ranch has greater effect than varying other flux variables.

California, Nevada↗
USGS1987

Geologic structure and altitude of the top of the Minnelusa Formation, northern Black Hills, South Dakota and Wyoming, and Bear Lodge Mountains, Wyoming

Beginning in 1981, a 3-yr project was conducted to determine the availability and quality of groundwater in the sedimentary bedrock aquifers in the Black Hills of South Dakota and Wyoming. The project was limited to three bedrock units in order of increasing age: the Cretaceous Inyan kara Group, Permian and Pennsylvanian Minnelusa Formation, and Mississippian Madison (or Pahasapa) Limestone. This map shows the altitude of the top of the Minnelusa Formation in the northern Black Hills, and shows the configuration of the structural features in the northern part of the Black Hills and the eastern part of the Bear Lodge Mountains. In general, the Minnelusa Formation dips away from the Black Hills uplift, either to the northeast and the Williston Basin or, south of the Bear Lodge Mountains, to the southwest and the Powder River basin, which is outside the map area. In the map area, the upper beds of the Minnelusa Formation are an aquifer and the lower beds are a confining or semi-confining unit. The upper part of the Minnelusa Formation has a greater percentage of coarse-grained sandstone beds than the lower part. Furthermore, solution and removal of anhydrite, brecciation, and solution of cement binding the sandstone grains may have increased the permeability of the upper part of the Minnelusa Formation in the Black Hills. Wells completed in the upper part of the Minnelusa have yields that exceed 100 gal/min in some areas and at least one large diameter well is reported to flow 1,000 gal/min in some areas and at least one large diameter well is reported to flow 1,000 gal/min. Flowing wells have been completed in the Minnelusa aquifer in most of the study area in South Dakota and in about the northern one-half of Crook County, Wyoming. (Lantz-PTT)

Water-Resources Investigations Report↗
USGS1987

Sediment discharge in Muddy Creek and the effect of sedimentation rate on the proposed Wolford Mountain reservoir near Kremmling, Colorado

Stream-discharge data collected from May 1982 through October 1985 and sediment data collected from March 1985 through October 1985 at stream flow-gaging station 09041500 Muddy Creek at Kremmling, Colorado, were used to determine total-sediment discharge into the proposed Wolford Mountain Reservoir. The data were divided on a seasonal basis, and statistical relations between suspended-sediment discharge and stream discharge were determined for the rising stage, falling stage, and base-flow period. One statistical relation between bedload discharge and stream discharge was determined from all collected data. These relations were used with 3 years of daily stream-discharge data to estimate total-sediment discharge. Total-sediment discharge was largest prior to the annual peak stream discharge during the study period and decreased thereafter. At least 97% of the total-sediment discharge was suspended sediment. Mean annual total-sediment discharge in Muddy Creek near Kremmling was estimated to be 83,000 tons per year for the 1983 through 1985 water years. Water-storage capacity of the proposed Wolford Mountain Reservoir at site C would decrease 10% after 100 years at this rate of mean annual total-sediment discharge. (USGS)

Water-Resources Investigations Report↗
USGS1993

Preliminary hydrogeologic assessment of boreholes UE-25c #1, UE-25c #2, and UE-25c #3, Yucca Mountain, Nye County, Nevada

Boreholes UE-25c #1, UE-25c #2, and UE-25c #3 (collectively called the C-holes) each were drilled to a depth of 914.4 meters at Yucca Mountain, on the Nevada Test Site, in 1983 and 1984 for the purpose of conducting aquifer and tracer tests. Each of the boreholes penetrated the Paintbrush Tuff and the tuffs and lavas of Calico Hills and bottomed in the Crater Flat Tuff. The geologic units penetrated consist of devitrified to vitrophyric, nonwelded to densely welded, ash-flow tuff, tuff breccia, ash-fall tuff, and bedded tuff. Below the water table, which is at an average depth of 401.6 meters below land surface, the rocks are argillic and zeolitic. The geologic units at the C-hole complex strike N. 2° W. and dip 15° to 21° NE. They are cut by several faults, including the Paintbrush Canyon Fault, a prominent normal fault oriented S. 9° W., 52.2° NW. The rocks at the C-hole complex are fractured extensively, with most fractures oriented approximately perpendicular to the direction of regional least horizontal principal stress. In the Crater Flat Tuff and the tuffs and lavas of Calico Hills, fractures strike predominantly between S. 20° E. and S. 20° W. and secondarily between S. 20° E. and S. 60° E. In the Topopah Spring Member of the Paintbrush Tuff, however, southeasterly striking fractures predominate. Most fractures are steeply dipping, although shallowly dipping fractures occur in nonwelded and reworked tuff intervals of the Crater Flat Tuff. Mineral-filled fractures are common in the tuff breccia zone of the Tram Member of the Crater Flat Tuff, and, also, in the welded tuff zone of the Bullfrog Member of the Crater Flat Tuff. The fracture density of geologic units in the C-holes was estimated to range from 1.3 to 7.6 fractures per cubic meter. Most of these estimates appear to be the correct order of magnitude when compared to transect measurements and core data from other boreholes 1.3 orders of magnitude too low. Geophysical data and laboratory analyses were used to determine matrix hydrologic properties of the tuffs and lavas of Calico Hills and the Crater Flat Tuff in the C-holes. The porosity ranged from 12 to 43 percent and, on the average, was larger in nonwelded to partially welded, ash-flow tuff, ashfall tuff, and reworked tuff than in moderately to densely welded ash-flow tuff. The pore-scale horizontal permeability of nine samples ranged from 5.7x10 -3 to 2.9 millidarcies, and the pore-scale vertical permeability of these samples ranged from 3.7x10 -3 to 1.5 millidarcies. Ratios of pore-scale horizontal to vertical permeability generally ranged from 0.7 to 2. Although the number of samples was small, values of pore-scale permeability determined were consistent with samples from other boreholes at Yucca Mountain. The specific storage of nonwelded to partially welded ash-flow tuff, ash-fall tuff, and reworked tuff was estimated from porosity and elasticity to be 2x10 -6 per meter, twice the specific storage of moderately to densely welded ash-flow tuff and tuff breccia. The storativity of geologic units, based on their average thickness (corrected for bedding dip) and specific storage, was estimated to range from 1x10 -5 to 2x10 -4 .

Nevada↗
USGS1992

Seasonal changes in ground-water quality and ground-water levels and directions of ground-water movement in southern Elmore County, southwestern Idaho, including Mountain Home Air Force Base, 1990-91

The study area is located in southern Elmore County, southwestern Idaho, and includes the Mountain Home Air Force Base located approximately 10 mi southwest of the city of Mountain Home. Chemical analyzes have been made periodically since the late 1940's on water samples from supply wells on the Air Force Base. These analyses indicate increases in specific conductance and in concentrations of nitrogen compounds, chloride, and sulfate. The purposes of this report, which was prepared in cooperation with the Department of the Air Force, are to describe the seasonal changes in water quality and water levels and to depict the directions of ground-water movement in the regional aquifer system and perched-water zones. Although data presented in this report are from both the regional ground-water system and perched-water zones, the focus is on the regional system. A previous study by the U.S. Geological Survey (Parliman and Young, 1990) describes the areal changes in water quality and water levels during the fall of 1989. During March, July, and October 1990, 141 wells were inventoried and depth to water was measured. Continuous water-level recorders were installed on 5 of the wells and monthly measurements of depth to water were made in 17 of the wells during March 1990 through February 1991. Water samples from 33 wells and 1 spring were collected during the spring and fall of 1990 for chemical analyses. Samples also were collected monthly from 11 of those wells during April to September 1990 (table 1). Selected well-construction and water-use data and measurements of depth to water for 141 wells are given in table 2 (separated sheets in envelope). Directions of ground-water movement and selected hydrographs showing seasonal fluctuations of water levels in the regional ground-water system and perched-water zones are shown on sheet 2. Changes in water levels in the regional ground-water system during March to October 1990 are shown on sheet 2.

Idaho↗
USGS1998

Characterization of hydrogeologic units using matrix properties, Yucca Mountain, Nevada

Determination of the suitability of Yucca Mountain, in southern Nevada, as a geologic repository for high-level radioactive waste requires the use of numerical flow and transport models. Input for these models includes parameters that describe hydrologic properties and the initial and boundary conditions for all rock materials within the unsaturated zone, as well as some of the upper rocks in the saturated zone. There are 30 hydrogeologic units in the unsaturated zone, and each unit is defined by limited ranges where a discrete volume of rock contains similar hydrogeologic properties. These hydrogeologic units can be easily located in space by using three-dimensional lithostratigraphic models based on relation- ships of the properties with the lithostratigraphy. Physical properties of bulk density, porosity, and particle density; flow properties of saturated hydraulic conductivity and moisture-retention characteristics; and the state variables (variables describing the current state of field conditions) of saturation and water potential were determined for each unit. Units were defined using (1) a data base developed from 4,892 rock samples collected from the coring of 23 shallow and 8 deep boreholes, (2) described lithostratigraphic boundaries and corresponding relations to porosity, (3) recognition of transition zones with pronounced changes in properties over short vertical distances, (4) characterization of the influence of mineral alteration on hydrologic properties such as permeability and moisture-retention characteristics, and (5) a statistical analysis to evaluate where boundaries should be adjusted to minimize the variance within layers. This study describes the correlation of hydrologic properties to porosity, a property that is well related to the lithostratigraphy and depositional and cooling history of the volcanic deposits and can, therefore, be modeled to be distributed laterally. Parameters of the hydrogeologic units developed in this study and the relation of flow properties to porosity that are described can be used to produce detailed and accurate representations of the core-scale hydrologic processes ongoing at Yucca Mountain.

Nevada↗
USGS1961

Exploratory drilling for ground water in the Mountain Iron-Virginia area, St. Louis County, Minnesota

The Mountain Iron-Virginia area is a broad, southwest-trending valley in the central part of the Mesabi Range. The valley, which heads in the Laurentian Divide, and covers about 120 square miles, coincides approximately with a bedrock valley filled with as much as 150 feet of glacial deposits. A complex sequence of glacioaqueous sediments made up of clay, silt, sand, and gravel was delineated from test holes drilled at 238 sites. These sediments range in thickness from 0 to 125 feet and can be considered a hydrologic unit, bounded below by sandy till or bedrock and above by as much as 60 feet of clayey till. The piezometric surface ranges from 0 to about 70 feet below land surface, thus, the glacioaqueous deposits are not everywhere completely saturated. In places, however, the water is under artesian pressure. Within the Mountain Iron-Virginia area about 50 square miles are underlain by deposits 20 feet or more in thickness of silt, sand, or gravel that constitute an aquifer that is a large potential source for additional water supplies. Except for iron and manganese, which are present in excessive amounts in some wells, the water meets U.S. Public Health Service standards for municipal supplies. Pumping tests of wells in the permeable sand or gravel deposits at five sites indicate that yields of several hundred gallons per minute and possibly as much as 2,000 gpm (gallons per minute) can be expected.

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