A Comparative Risk Analysis of Drinking Water Contaminants in California. P. R. D. Williams and P. J. Sheehan, Exponent
The California Department of Health Services (CDHS) maintains a drinking water monitoring database for large and small systems in the State. The CHDS database currently contains about 9.5 million drinking water records and sample data for over 450 chemicals. Information is also provided for sample date, source and system name, county, chemical concentration or detection limit (if a non-detect sample), type of water source (groundwater or surface water), operation status of well (e.g., abandoned, inactive, active, etc.), and population served by each water system. The purpose of this paper is to evaluate the detection frequencies and average concentrations of a range of contaminants in California drinking water, particularly those that co-occur in the same drinking water source. Detected chemical concentrations are compared to various regulatory standards in California, including enforceable Maximum Contaminant Levels (MCLs), health-based Primary MCLs, and aesthetic-based Secondary MCLs. Potential human exposures from the consumption of contaminated drinking water, and related health risks, are also assessed. The comparative risk analysis includes more than 10 chemicals that are detected frequently in drinking water and are classified by the U.S. Environmental Protection Agency as "known" or "potential" human carcinogens, such as benzene, bromoform, carbon tetrachloride, chloroform, dichloroethylene, tetrachlorethane, and trichloroethylene. Although not formally classified as a human carcinogen, methyl tertiary butyl ether (MTBE) is also included in the analysis, given the recent controversy over this chemical in California’s drinking water. The results of this analysis will provide useful information on the incidence and relative risks of different drinking water contaminants in California, which can be used to prioritize public health hazards and aid in the development of appropriate risk mitigation efforts.
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