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Classifying Drinking Water Contaminants for Regulatory Consideration
plies utilized by interstate carriers such as buses, trains, airplanes, and ships (NRC, 1997). The reader should refer to the 1997 National Research Council (NRC) report Safe Water from Every Tap: Improving Water Service to Small Communities (NRC, 1997) for an abbreviated review of the historical development of drinking water supply regulations in the United States. Alternatively, Pontius and Clark (1999) provide an extensive overview and discussion of this topic, especially as related to the SDWA and its subsequent amendments.
The purpose of the original SDWA was to ensure that public water systems (PWSs)1 meet national primary drinking water regulations2 for contaminants to protect public health. The SDWA also established a joint federal-state system to help administer the nationwide program and ensure compliance with federal standards. It is important to note that the SDWA does not regulate bottled water. Rather, bottled water is regulated at the federal level by the U.S. Food and Drug Administration under authority of the Federal Food, Drug, and Cosmetic Act. This report is concerned principally with requirements newly established in the SDWA Amendments of 1996.
Among other changes, the amended SDWA requires EPA to publish a list of unregulated contaminants and contaminant groups every five years that are known or anticipated to occur in public water systems and which may require regulation. This list, the Drinking Water Contaminant Candidate List—commonly referred to as the CCL—will provide the
Public water systems subject to regulation under the amended SDWA are defined as distribution systems that provide water for human consumption through “constructed conveyances” (e.g., pipe networks, irrigation ditches) to at least 15 service connections or an average of 25 individuals daily for at least 60 days per year (EPA, 1998b).
For chemical contaminants, a national primary drinking water regulation includes a nonenforceable criterion called the maximum contaminant level goal (MCLG) that is used to help set an enforceable standard called the maximum contaminant level (MCL) or treatment techniques (if contaminant monitoring is deemed not feasible). In general, MCLs are set as close to the MCLG as feasible, depending on risk management considerations such as an EPA determination that the cost of a setting an MCL at the MCLG is not justified by the benefits (EPA, 1996a). For microbiological contaminants, the original SDWA philosophically established a zero tolerance for disease-causing organisms as the health goal (i.e., the MCLG is set at zero). In practice, however, treatment performance techniques, rather than specific allowable concentrations of pathogens (such as MCLs), historically have served as the basis for regulating microbial contaminants in drinking water (NRC, 1999a).