Quantitative Evaluation of Regulatory Indicators for Brominated Haloacetic Acids in Drinking Water

Drinking water regulations often use indicators to represent risk associated with broader contaminant groups. To evaluate the efficacy of indicators, a quantitative approach is needed that aligns with the regulatory framework, in which a benchmark value represents an unacceptably high level of a contaminant or contaminant class. This policy microsimulation study develops such an approach in the context of potential regulatory revisions to address brominated HAAs, a class of disinfection byproducts. Likely scenarios include a limit on the sum of nine brominated and chlorinated HAAs (HAA9), on bromide, or on the sum of six brominated HAAs (HAA6Br). The probability of each potential regulatory indicator co-occurring with a high level of HAA6Br was quantified using logistic models. The HAA9 and bromide indicators both performed poorly, with no better than a ∼1 in 4 chance of identifying equivalently high levels of HAA6Br. Furthermore, high false positive rates (>75%) would implicate a substantial number of water systems that do not have high HAA6Br levels. This study reveals the trade-off implicit in the use of regulatory indicators, in which precision (fewer false positives) must be sacrificed to achieve greater coverage (more true positives). The methodology and findings have broad implications for evaluating indicator classes in drinking water policy and research.