Chemicals in California drinking water: source contaminants, risk assessment, risk management, and regulatory standards

Monitoring studies from 1983 to 1992 of water supply and drinking water wells in the state for organic contaminants indicated that more than 80 chemicals were present in ground water. Most of the chemicals detected occurred infrequently and at levels below the current water quality criteria (maximum contaminant level, MCL, or action level, AL). Drinking water wells with levels exceeding these criteria were either closed or had remedial actions taken. Dibromochloropropane (DBCP), simazine, diuron, atrazine, tetrachloroethylene (PCE), and trichloroethylene (TCE) were some of the chemicals detected most frequently in these studies. DBCP, simazine, diuron, and atrazine are agricultural pesticides and are either no longer registered or restricted for use as active ingredients. Special chemical contaminants of concern in ground water are nitrate, arsenic, fluoride, and radon. Surface water from rain and snow runoffs from the Sierra Nevada provides drinking water for most of the San Francisco Bay Area. This water is considered pristine and requires only treatment against disease-causing microorganisms. Most of Southern California depends on surface water from the Sacramento-San Joaquin River Delta and the Colorado River. The quality of water in the Delta is affected by discharges of pollutants into the watersheds of the Sacramento and San Joaquin Rivers and the intrusion of seawater from the San Francisco Bay. The major concern of most water utilities with regard to the use of Delta water for drinking is the formation of trihalomethanes (THMs) and other disinfection by-products. California can promulgate its own regulations which are frequently more stringent than the federal regulations. Standards have also been established for many water contaminants that are uniquely found in California. This report presents the state and federal drinking water standards for 19 inorganic, 66 organic, and 10 other chemicals, mainly radionuclides.