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GSA Special Paper 381.

Pahute Mesa was the principal site for underground nuclear tests in the United States, and Yucca Mountain is the proposed site for this nation’s first permanent high-level nuclear-waste repository. This paper interprets results of hydraulic tests from 41 sites in the Yucca Mountain–Pahute Mesa area, emphasizing 46 new or revised test analyses. Methods used to analyze data account for the dual fracture and matrix permeability of the tuffaceous rocks and lava flows. Because these rocks are unlike many commonly studied aquifer systems, some conventional analytical methods used for pumping tests in porous media could not be used or had to be used with caution. Hydraulic conductivity obtained from drawdown in a pumped well was observed to be comparable to hydraulic conductivity obtained from slug-injection and swabbing-recovery tests but much smaller than hydraulic conductivity obtained from observation-well data. The length of a pumping test also was found to influence the shape of the drawdown curve and, hence, the determination of hydraulic properties. Many pumping test analyses illustrate conclusions about flow-system dynamics and hydraulic properties presented in the paper.