California ground-water quality

Abstract

Nearly 18 million people, about 69 percent of the population of California (fig. 1) rely on groundwater supplies. Ground water in principal aquifers (fig. 2) may not be suitable for all public-supply, domestic, agricultural, and industrial uses because of dissolved minerals or temperature but may support selected uses consistent with the quality of the water. The California State Water Resources Control Board (SWRCB) made a groundwater-quality assessment from 1984 to 1985 based on designated water use in 139 of 461 groundwater basins in the State identified by the California Department of Water Resources (DWR). The 139 basins comprise 79 percent of the surface area of all basins and include the top-priority basins based on population, use, and water-quality problems. Groundwater quality in the 139 basins is generally good, based on criteria established by SWRCB. Seventy-six percent of the groundwater basins assessed support designated water uses; whereas, 14 percent partially support uses. Water quality is unknown in about 8 percent of the basins assessed. Ground water of poor quality was found in parts or all of 21 basins (California State Water Resources Control Board, 1986). At 71 hazardous-waste sites (fig. 3), monitoring and evaluation of groundwater quality is required by the Federal Resource Conservation and Recovery Act (RCRA) of 1976. In addition to the RCRA sites, 34 other sites are included by the U.S. Environmental Protection Agency (EPA) in the National Priorities List (NPL) of hazardous-waste sites (U.S. Environmental Protection Agency, 1986c) under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) of 1980. Groundwater contamination from organic solvents, pesticides, acids, and trace metals has been detected at 26 of the 34 CERCLA sites. The California Department of Health Services (DOHS) has about 120 additional sites on a State toxic substances priority list where monitoring and evaluation are in progress. Twenty-three sites on 12 military installations were recommended for cleanup in phase IV of the U.S. Department of Defense (DOD) Installation Restoration Program (IRP), and remedial action has been completed at 11 sites as of September 1985. Numerous groundwater quality monitoring programs are conducted by other Federal, State, and local agencies. The DWR and cooperating agencies, including the U.S. Geological Survey, collect and analyze B Figure 1. Selected geographic features and 1985 population distribution in California. A.