Identification and characterization of hydrologic properties of fractured tuff using hydraulic and tracer tests, test well USW H-4, Yucca Mountain, Nye County, Nevada
Test well USW H-4, located on the eastern edge of Yucca Mountain, Nye County, Nevada, penetrates volcanic tuffs through which water moves primarily along fractures. Data, collected from hydrologic and tracer tests and an acoustic-televiewer log, were used to quantify intrawell-bore flow directions and rates, permeability distribution, fracture porosity, and orientations of the hydraulic-conductivity ellipsoid for the test well. Borehole temperature data collected during a pumping test were used to identify 33 locations at which water was entering the hole. These results correlated well with results from radioactive-tracer surveys and packer tests of isolated intervals. Iodine-131 was used as a tracer under nonpumping conditions to study flow within the borehole, and to identify fractures that produced or accepted water. Water within the borehole was moving down from above and up from below toward the interval between 2500 and 3070 feet. Inflow and outflow were detected in the two most permeable zones in the borehole; however, the nondetection of it in the other test intervals may have resulted from monitoring periods that were too short. In the uppermost permeable zone, water moved down from above 2365 feet and exited the borehole between 2365 to 2375 feet; freshwater entered the borehole between 2380 and 2385 feet and moved downward. The probable shape and orientation of the hydraulic-conductivity ellipsoid were calculated from fracture frequency and orientation data. The plane containing the two larger principal axes of the ellipsoid strikes approximately north 23{sup 0} east and is nearly vertical. These two axes are approximately the same magnitude and are five to seven times larger than the smallest axis. Fracture porosity is about 10{sup -4} to 10{sup -3}, as estimated from the cubic law for hydraulic conductivity of fractures. 13 refs., 7 figs., 4 tabs.
- Research Organization:
- US Geological Survey, Denver, CO (United States)
- DOE Contract Number:
- AI08-78ET44802
- OSTI ID:
- 59708
- Report Number(s):
- USGS/WRI-85-4066; ON: DE85902212
- Resource Relation:
- Other Information: PBD: 1985
- Country of Publication:
- United States
- Language:
- English
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