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must be reduced to the MCL or, if there is an approved state plan, the risk to the population served by the water supply can be reduced by activities that reduce radon in air and/or water.
The committee discussed a variety of methods to reduce radon entry into homes and the concentrations in the indoor air and in water. Ventilation systems can be used to reduce radon concentrations in indoor air to acceptable levels. Periodic testing would be needed to ensure the continued successful operation of individual air treatment systems. New homes can be constructed using methods to reduce airborne radon (radon resistant construction). However, there is not enough evidence at the present time to be certain these techniques are effective. Several water-treatment technologies to remove radon from water are very effective, however, they do not address the largest risk to the occupants of the house, namely radon in air.
The EPA mandate is to reduce public risk caused by exposure to radon. For those communities where the public water supply contains radon at concentrations between the MCL and the AMCL, the law will allow individual states to reduce the risk to their population through multimedia measures to mitigate radon levels in indoor air. A state may develop and submit a multimedia program to mitigate radon levels in indoor air for approval by the EPA Administrator. The Administrator shall approve a state program if the health risk reduction benefits expected to be achieved by the program are equal to or greater than the health risk reduction benefits that would be achieved if each public water system in the state complied with the MCL. If the program is approved, public water systems in the state may comply with the alternative maximum contaminant level in lieu of the MCL. State programs may rely on a variety of mitigation measures, including public education, home radon testing, training, technical assistance, remediation grant and loan or other financial incentive programs, or other regulatory or nonregulatory measures. As required by SDWA, EPA is developing guidelines for multimedia mitigation programs. If there is no approved state multimedia mitigation program, any public water system in the state may submit a program for approval by the EPA Administrator, according to the same criteria, conditions and approval process that would apply to a state program. In this scenario, water utilities can minimize the level of risk to their consumers—even if the water they provide is higher than the MCL (but lower than the AMCL)—by reducing airborne radon in some of the community's homes. Because the risk caused by inhaled radon is so much greater than that caused by radon that is swallowed in water, reducing the airborne radon in only a few homes may reduce public risk enough for the water utility to be in compliance with the multimedia program requirements.
With regard to multimedia programs, the committee's report provides discussion of risk-reduction methods at the community level and of ways to evaluate the effectiveness of reducing radon-related risk within a community or region