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Addressing Risk-Balancing Considerations for Six-Year Review of Drinking Water Standards

Risk-balancing is applicable only to the microbial and disinifection byproducts (MDBP) rules, which were promulgated to address balancing between microbial and DBP requirements, and among differing types of DBPs. This effort was based on the SDWA requirement that EPA “minimize the overall risk of adverse health effects by balancing the risk from the contaminant and the risk from other contaminants the concentration of which may be affected by the use of a treatment techniqueHelptreatment techniqueA required process intended to reduce the level of a contaminant in drinking water. or process that would be employed to attain the maximum contaminant levelHelpmaximum contaminant levelThe highest level of a contaminant that is allowed in drinking water as delineated by the National Primary Drinking Water Regulations. These levels are based on consideration of health risks, technical feasibility of treatment, and cost-benefit analysis. or levels."

Risk-balancing is conducted to address whether a change to an MCLHelpMCLThe highest level of a contaminant that is allowed in drinking water as delineated by the National Primary Drinking Water Regulations. These levels are based on consideration of health risks, technical feasibility of treatment, and cost-benefit analysis. and/or treatment technique will affect the risk from one or more other contaminants, and, if so, to consider revisions that will balance these overall risks. This approach was used in the development of several rules, such as those for the Long-Term 2 Enhanced Surface Water Treatment Rule and the Stage 2 Disinfectants and Disinfection Byproducts Rule, promulgated in January 2006.

It considers whether a change to a National Primary Drinking Water Regulation (NPDWR) could affect the risk from one or more contaminants, and, if so, whether the change will increase the risks of adverse health effects from that contaminant. 

The output is a determination of whether additional revisions to the MCL and/or treatment technique are needed to help balance the overall risks from potential changes.