Water resources of the Descanso Area, San Diego County, California

Hydrologic information was collected during water year 1988 (October 1987 to September 1988) to evaluate the effects of current pumping on groundwater levels in the Descanso area in south-central San Diego County. Water year 1988 was a period of near-normal precipitation and runoff. The groundwater system in the area consists of aquifers in the metamorphic and granitic bedrock and in the overlying regolith (weathered bedrock). Most wells penetrate both aquifers, but the regolith is the source of most water pumped from wells. Groundwater storage in 1988 was estimated to be 800 to 2,000 acre-ft in the regolith and 300 to 3,000 acre-ft in bedrock. Recharge to the groundwater system from infiltration of precipitation and streamflow was estimated to be about 1,000 acre-ft. Pumpage, which was estimated to be 170 acre-ft, had little effect on groundwater storage. Water levels in wells were nearly the same at the end of the water year as at the beginning. Groundwater quality generally was suitable for domestic uses. Concentrations of iron and manganese , although nontoxic, exceeded California maximum contaminant levels for domestic drinking water in some wells. (USGS)