Porosity and permeability of tuffs from the unsaturated zone at Yucca Mountain, Nevada

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5862510

Soeder, D J; Dishart, J E ^[1]

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1. Geological Survey, Mercury, NV (United States)

An investigation of the intrinsic flow properties of the rock matrix in the unsaturated zone at Yucca Mountain, Nevada, was carried out by performing single-phase water or air permeability measurements on about 150 selected samples representing all of the different rock units in the unsaturated zone. Pores were studied by examining thin sections of samples impregnated with fluorescent-dyed epoxy. Yucca Mountain is made up of volcanic tuff, which occurs in three distinct textures: welded, nonwelded, and bedded. Welded tuffs occur in two thick, rhyolitic, pyroclastic flow units. In thin sections, the typical welded-tuff pore structure appears to consist of isolated voids interconnected by microfractures. Porosities average about 10 percent, and matrix permeabilities are generally 1 microdarcy or less. The nonwelded tuffs occur in several thin pyroclastic flows between and below the two main welded units. Porosities average about 20 to 30%, and permeabilities are in the microdarcy to millidarcy range. The nonwelded tuffs appear in thin sections to have an open, well-interconnected pore system with significant intragranular porosity in pumice and lithic grains. These tuffs often contain various amounts of secondary clay and zeolite minerals in the pores, which may account for the wide range in permeabilities. The bedded tuffs consist of friable, low-density volcanic ash with porosities of 50% or more and permeabilities often above 1 darcy. These tuffs are the most porous and permeable rock units in the unsaturated zone, and contain large intergranular pores and significant intragranular porosity in frothy pumice clasts. Results of this investigation will help improve the understanding of groundwater movement through the unsaturated zone.

• OSTI ID: 5862510
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

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DEVELOPED COUNTRIES
GROUND WATER
HYDROGEN COMPOUNDS
HYDROLOGY
MICROSTRUCTURE
MOUNTAINS
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PORE STRUCTURE
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YUCCA MOUNTAIN