ciently defensible, transparent, or available for public comment. In particular, several major policy decisions were made during the process that lacked sufficient explanation and justification. By identifying and thoroughly discussing these limitations, the committee aims to illustrate how important it is to arrive at a more systematic CCL development mechanism that directly addresses these and other sociopolitical issues. The committee notes that its second report (NRC, 1999b) also describes (albeit summarily) some limitations of the first CCL development process.

A major policy decision made during the development of the first CCL was to use completely separate approaches to evaluate potential chemical and microbiological drinking water contaminants. The committee believes that the justification given by EPA (EPA, 1997a) for conducting two independent assessments was not adequate and perpetuates the long-established and often unnecessary regulatory practice of treating chemical and microbial drinking water contaminants separately and differently. As reviewed in the committee’s first report (NRC, 1999a) and in more detail in Chapter 6 of this report, rather than regulating each type of microorganism to a specific concentration as done for chemicals, regulators historically have established a “zero-tolerance” goal for microbiological contaminants. Indicator organisms, particularly fecal coliforms, are then used to show the possible presence of microbial contamination resulting from human waste. While this approach has served well for indicating widespread sewage contamination of surface waters and for controlling diseases such as cholera and typhoid fever, several deficiencies in this approach have come to light in recent decades. For example, some bacteria and many viruses and protozoa show greater resistance to conventional treatment methods than do fecal coliforms. This approach has also led to a deficiency of occurrence databases for microbial contaminants. The committee continues to believe that the time is rapidly approaching when the same risk assessment principles should be applied to the management of microbial contaminants as are applied to chemical contaminants. Indeed, as described in Chapter 1 and elsewhere in this report, the committee recommends a two-step approach for the development of future CCLs that will similarly assess chemical, microbial, and other types of potential drinking water contaminants.

Second, all potential chemical drinking water contaminants that were considered initially for inclusion on the CCL were taken directly from existing databases and lists of chemicals produced by various regulatory programs within EPA and by stakeholder groups (see Table 1–1; EPA, 1997a). Although this was useful for developing a CCL in a short time

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