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Classifying Drinking Water Contaminants for Regulatory Consideration
for public and other stakeholder input and undergo scientific review. The committee also makes the following related recommendations:
The assessment of severity should be based, when feasible, on plausible exposures via drinking water. The committee also recommends that EPA give consideration to different severity metrics such as a ranking through use of either quality adjusted or disability adjusted life-years lost due to exposure to a contaminant.
Regarding the assessment of contaminant prevalence, in some cases (particularly where contaminants have been included on a PCCL on the basis of potential rather than demonstrated occurrence), information will often be insufficient to directly assess temporal or spatial prevalence (or both). Thus, EPA should consider the possibility of including information on temporal and regional occurrence to help determine (score PCCL) contaminant prevalence. When prevalence cannot be assessed, this attribute must then go unscored and the attribute of persistence-mobility used in its stead. The issue of changing (or incorporating) “thresholds” for contaminant detection, rather than relying on continually decreasing detection limits, is one that needs explicit attention and discussion by EPA and stakeholders.
Existing and readily available databases may not be sufficient to rapidly and consistently score health effect and occurrence attributes for individual PCCL contaminants for promotion to a CCL. As recommended in Chapter 3, all information from existing or created databases or lists used in the development of a CCL and PCCL, should be compiled in a consolidated database that would provide a consistent mechanism for recording and retrieving information on the PCCL contaminants under consideration. As a starting point and as recommended in Chapter 3, EPA should review its developing EDPSD database to determine if it can be expanded and used (or serve as a model for the development of) such a consolidated database and to help develop future PCCLs and CCLs.
Contaminant databases used in support of the development of future CCLs should report summary statistics on all data collected, not only the quantifiable observations. In this regard, EPA should formalize a process for reporting means and/or medians from data with large numbers of nondetect observations. In addition, EPA may want to consider providing other measures of concentration in water supplies such as the 95th percentile of contaminant concentration.