Introduction • Location of Study Area • Regional Geology • Regional Groundwater Hydrology • Hydrostratigraphic Units • Groundwater in the Younger Tertiary Tuff and Lava Flows Hydrostratigraphic Unit • Hydraulic Tests • Well Completion and Instrumentation • Flow Distribution in Boreholes • Earth Tides and Barometric Effects • Analytical Methods • Constant-Rate Pumping, Injection, and Airlift Tests • Slug-Injection and Swabbing Recovery Tests • Analytical Uncertainty • Effects of Test Scale on Determination of Hydraulic Properties • Hydraulic Properties • The C-holes Complex • Pumping Test in UE-25 c#3, May 22 to June 1, 1995 • Miscellaneous Hydraulic Tests at the C-holes Complex, 1984–1998 • Pumping Test in UE-25 c#3, May 8, 1996, to November 12, 1997 • Drill Hole Wash • Frenchman Flat • Well Cluster ER-20-6, Western Pahute Mesa • Knickerbocker Site, Western Pahute Mesa • Distribution of Hydraulic Conductivity • Relation of Lithology to Hydraulic Conductivity • Hydraulic Conductivity Distribution at Yucca Mountain • Hydraulic Conductivity Distribution at Pahute Mesa • Summary and Conclusions • Appendix A • Appendix B • References Cited