Conceptual hydrologic model of flow in the unsaturated zone, Yucca Mountain, Nevada

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Authors:Montazer, Parviz; Wilson, William E.
Author Affiliations:Primary:
U. S. Geol. Surv., Lakewood, CO, United States
Source:Reston, VA [Water-Resources Investigations - U. S. Geological Survey, No.WRI84-4345, 55p. Publisher: U. S. Geological Survey,], United States. ISSN: 0092-332X
Publication Date:1984
Note:In English. 41 refs.
Summary:Yucca Mountain consists of a series of north-trending fault-block ridges composed of volcanic rocks that have an eastward tilt of about 5 to 30 degrees. Thickness of the unsaturated zone is about 500 to 750 meters. Three formations of ash-flow tuff occur beneath the alluvium: Paintbrush Tuff, tuffaceous beds of Calico Hills, and Crater Flat Tuff. Based on physical properties, the rocks in the unsaturated zone are grouped for the purpose of this report into five informal hydrogeologic units: Tiva Canyon welded unit, Paintbrush nonwelded unit, Topopah Spring welded unit, Calico Hills nonwelded unit, and Crater Flat unit. Welded units have a mean fracture density of 8 to 40 fractures per cubic meter, mean matrix porosities of 12 to 23 percent, matrix hydraulic conductivities with geometric means ranging from 2 × 10-6 to 3 × 10-6 meter per day, and bulk hydraulic conductivities of 0.1 to 10 meters per day. The nonwelded units have a mean fracture density of 1 to 3 fractures per cubic meter, matrix porosities of 31 to 46 percent, and variable hydraulic conductivities, with geometric means ranging from 8 × 10-6 to 9 × 10-3 meter per day. The central block (the primary repository area being evaluated by the U.S. Department of Energy) is bounded by steeply dipping faults or by fault zones. The central block is relatively intact and is transected by a few normal faults. A hypothetical model is proposed for flow through porous layers intercalated with double-porosity layers. In this model, flow through fractures can occur at almost all stages of saturation, but the flux magnitude in fractures is largely a factor of the contrast between the matrix and fracture hydraulic properties and the magnitude of the perturbation of flux at the flow boundaries. Modified author abstract.
Subjects:Cenozoic; Crater Flat Tuff; Engineering geology; Faults; Ground water; High-level waste; Host rocks; Hydraulic conductivity; Igneous rocks; Miocene; Movement; Neogene; Normal faults; Paintbrush Tuff; Physical properties; Pyroclastics; Radioactive waste; Site exploration; Surveys; Tertiary; Tuff; Underground storage; Unsaturated zone; USGS; Volcanic rocks; Waste disposal; Welded tuff; Nevada; Nevada Test Site; Nye County Nevada; United States; Yucca Mountain; Calico Hills Tuff
Coordinates:N365000 N365500 W1162000 W1163000
Record ID:1985063660
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute.
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