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A. L. Geldon

Publications and source records attributed to A. L. Geldon.

5 recordsLinked to original sources
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↗
USGS1985

Water resources of the Cottonwood Wash Watershed, Ute Mountain Ute Indian Reservation, southwestern Colorado

Cottonwood Wash, near Towaoc, Colorado, is a 16-square-mile watershed with an estimated average annual precipitation influx of 14,600 acre-feet. Most of this water is consumed by evapotranspiration. Except for snowmelt in the spring months and infrequent rain storms, all flow in the wash is from springs issuing from talus, block rubble, alluvium, colluvium, and Mancos Shale. Flow is greatest during the spring months when the ground is saturated from snowmelt and least during the early fall when many springs cease flowing. Most of the water in the wash upstream from Towaoc is diverted to Cottonwood Reservoir. Springs in the wash downstream from Towaoc are distributary. Most of the water from these springs, however, seeps back into the alluvium. One of these springs supplies about 19 acre-feet of water per year to Towaoc. The cumulative flow from 17 springs and diffuse seepage was about 290 acre-feet in the 1982 water year. The quantity of recoverable water in the younger of two pediment deposits is about 2,000 to 4,000 acre-feet, depending on seasonal and yearly variations in precipitation. Estimated underflow from the wash in the 1982 water year was 740 acre-feet; estimated recharge to bedrock was 850 acre-feet. Water from block rubble and talus is suitable for most purposes; water from Mancos Shale and alluvium may contain concentrations of dissolved solids that are unacceptable for domestic use. (USGS)

Water-Resources Investigations Report↗