The discharge of 3 acre-feet (4 x 10-3 cubic hectometres) per year of Class-I wastes in the Haystack Butte area of Edwards Air Force Base, Calif., has been proposed by the Air Force. Evaporation in this arid basin exceeds the 4 inches (100 millimetres) of annual precipitation. Fifteen test holes, ranging in depth from 40 to 240 feet (12 to 73 metres) below land surface, indicate that ground water occurs mostly in Tertiary volcanic and sedimentary rocks overlying pre-Tertiary quartz monzonite. Depth to water averages about 100 feet (30 metres) below land surface. Hydraulic conductivity of cores of Tertiary rock taken from a test hole at depths of 9 to 88 feet (2.7 to 27 metres) below land surface suggests values of 6.9 x 10-5 to 4.9 x 10-3 feet per day (2.1 x 10-5 to 1.5 x 10-3 metres per day). Petrographic analyses of these cores indicate a material consisting mostly of weathered volcanic rocks with a moderate concentration of montmorillonite clay.
The water-level gradient averages about 4 feet per mile (0.76 metre per kilometre). Ground-water discharge through a narrow gap in the southeastern part of the basin is calculated to be 3.8 x 10-4 acre-feet (4.7 x 10-7 cubic hectometres) per year. After leaving the basin, the underflow becomes part of a regional flow system discharging into Harper Lake playa.
An increase in the underflow from 3.8 x 10-4 acre-feet (4.7 x 10-7 cubic hectometres) per year to 3 acre-feet (4 x 10-3 cubic hectometres) per year may result in an undesirable surface-water flow by increasing the saturated thickness of the aquifer near the narrow gap in the southeastern part of the basin. Also, the very low hydraulic-conductivity values suggest that some difficulties may exist in percolating 3 acre-feet (4 x 10-3 cubic hectometres) per year of wastes resulting in possible saturation of the ground surface outside the boundaries of the potential Class-I site. Because the rate of evaporation is very high (116 inches or 294.6 millimetres per year) in the study area, many of the problems associated with the percolation of the waste water and the subsequent changes in ground-water movement could be minimized by evaporating the wastes to complete dryness.
The quality of the ground water in the basin is generally unsuitable for domestic, industrial, and irrigation purposes. The concentration and type of chemical constituents in the ground water suggest slow circulation in a geologic environment with soluble minerals.
Hydrologic evaluation of the Haystack Butte area : with emphasis on possible discharge of class-I wastes, Edwards Air Force Base, California