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Statement of Need: Radon in drinking water increases risk to public health, both from inhalation of radon discharged through normal water use, such as showering, and from ingestion of water.

Summary of the Legal Basis: Pursuant to the Safe Drinking Water Act, as amended in 1996 [sec. 1412 (b)(13)], EPA is required to: (1) Withdraw the 1991 proposed radon in drinking water rule; (2) Work with the National Academy of Sciences to conduct a risk assessment for radon in drinking water, and an assessment of the health risk reduction benefits associated with various mitigation methods of reducing radon in indoor air; (3) Publish a radon health risk reduction and cost analysis for possible radon Maximum Contaminant Levels (MCLs) for public comment, by February, 1999; (4) Propose a Maximum Contaminant Level Goal (MCLG) and National Primary Drinking Water Regulation (NPDWR) for radon by August, 1999; and (5) Publish an MCLG and Final NPDWR one year after proposal. In addition, if EPA promulgates an MCL more stringent than necessary to reduce the contribution of radon in indoor air from drinking water to a concentration that is equivalent to the national average concentration of radon in outdoor air, the Agency must establish an alternative MCL (AMCL). The AMCL is to be set at a level which would result in a contribution of radon from drinking water to radon levels in indoor air equivalent to the national average concentration of radon in outdoor air. If an alternative MCL is established, EPA must publish criteria for States to develop multimedia radon mitigation programs. EPA shall approve State multimedia mitigation programs if they are expected to achieve equal or greater health risk reduction benefits than would be achieved through compliance with the MCL. If EPA approves a State multimedia mitigation program, public water supply systems within the State may comply with the AMCL. If a State does not have an approved multimedia mitigation program, any public water system may submit a program for approval by EPA according to the same criteria, conditions, and approval process that would apply to a State program. EPA shall evaluate multimedia mitigation programs every 5 years.

Alternatives: EPA considered a range of MCL options for radon in drinking water in the Health Risk Reduction and Cost Analysis (HRRCA) (published in February 1999). The primary alternative is for a State or public water system to develop a multimedia mitigation program in order for it to comply with the AMCL. The National Academy of Sciences provided information on key factors (the water to air transfer factor and the national average outdoor radon level) that EPA used in setting the proposed AMCL.

Anticipated Costs and Benefits: The total annual costs of compliance with the MCL of 300 pCi/l for radon in drinking water and the associated information collection and reporting requirements is estimated at $341-408 million. In complying with 300 pCi/l, an estimated 62.0 fatal and 3 non-fatal cancer cases are avoided each year. Because EPA expects that most States and systems will choose to comply with the alternative maximum contaminant level (AMCL) of 4,000 pCi/l and implement a Multi-Media Mitigation (MMM) program, EPA expects the total annual costs of compliance with the radon rule to be significantly less than $408 million. If most States and systems comply with the AMCL and implement a MMM program, the total annual costs of compliance are estimated at approximately $86 million. The quantifiable benefits of the health risk reduction are estimated to be $360 million for either implementation scenario. EPA expects compliance with the AMCL and implementation of a MMM program to achieve equal or greater risk reduction than is expected with strict compliance with the MCL.

Risks: Radon is a naturally occurring volatile gas formed from the normal radioactive decay of uranium. It is colorless, odorless, tasteless, chemically inert, and radioactive. Exposure to radon and its progeny is believed to be associated with increased risks of several kinds of cancer. When radon or its progeny are inhaled, lung cancer accounts for most of the total incremental cancer risk. Ingestion of radon in water is suspected of being associated with increased risk of tumors of several internal organs, primarily the stomach. As required by the SDWA, as amended, EPA arranged for the National Academy of Sciences (NAS) to assess the health risks of radon in drinking water. The NAS Report represents a comprehensive assessment of scientific data gathered to date on radon in drinking water. The report, in general, confirms earlier EPA scientific conclusions and analyses of radon in drinking water. The NAS Report is one of the most important inputs used by EPA in its regulatory impact analysis. EPA has used the NAS?s assessment of the cancer risks from radon in drinking water to estimate both the health risks posed by existing levels of radon in drinking water and also the cancer deaths prevented by reducing radon levels.