A 10,365-ft deep test hole drilled at the INEL (Idaho National Engineering Laboratory) in southeastern Idaho provided hydraulic information for rock units underlying the Snake River Plain aquifer. Four aquifer tests showed that the hydraulic conductivity decreased with depth--from an average of 0.03 ft/day for the interval from 1,511 to 2,206 ft below land surface to an average of 0.002 ft/day for the interval from 4 ,210 to 10,365 ft. In contrast the hydraulic conductivity of the Snake River Plain aquifer ranges from 1 to 100 ft/day. The hydraulic head increased with depth; the head at depth was about 115 ft greater than that for the Snake River Plain aquifer. Water temperature in the test hole increased from 26 C at 600 ft below land surface to 146 C at 9,985 ft. The gradient was nearly linear and averaged about 1.3 C/100 ft of depth. Water from the Snake River Plain aquifer contained 381 mg/L of dissolved solids and had a calcium bicarbonate chemical composition. The dissolved solids concentration in underlying rock units ranged from 350 to 1,020 mg/L and the water had a sodium bicarbonate composition. Hydrologic data for the test hole suggest that the effective base of the Snake River Plain aquifer near the test hole is between 840 and 1,220 ft below land surface. The upward vertical movement of water into the Snake River Plain aquifer from underlying rock units could be on the order of 15,000 acre-ft/year at INEL. (Author 's abstract)