The proposal allows states to focus on radon -in indoor air – seen as incurring the greatest public health risks – while also reducing the risks from radon in drinking water.

Radon is a naturally occurring radioactive breakdown product of uranium that can dissolve and accumulate in ground water. However, the primary source of human exposure to radon is breathing radon in indoor air of homes. Radon can enter indoor air from soil under foundations. Nearly 90 percent of the risk from radon in drinking water comes from breathing radon released to indoor air from household water uses. Radon is the second leading cause of lung cancer in the United States, after smoking.

The EPA’s proposal would provide two options to states and water systems for reducing public health risks from radon in both drinking water and indoor air.

Under the first option, states can develop programmes to address radon in indoor air in conjunction with individual water systems meeting a drinking water standard of 4,000 picoCuries per liter of water (pCi/L, a standard unit of radiation).

EPA is encouraging states to adopt this more cost-effective approach, which would address radon in indoor air while requiring individual water systems to reduce the higher levels of radon in drinking water. If a state does not elect this option, individual water systems in that state would either reduce radon in their system’s drinking water to 300 pCi/L or develop individual indoor air radon programmes and reduce levels in drinking water to 4,000 pCi/L. Water systems already at or below the 300 pCi/L standard will not be required to treat their water for radon.

EPA estimates the costs to states and community water systems of the more cost-effective approach, i.e., reducing radon in indoor air while implementing the 4,000 pCi/L drinking water standard, to be approximately $86 million a year. Treating drinking water from all community ground water sources to 300 pCi/L would cost states and systems about $407 million a year.

The proposed drinking water standards would apply only to community water systems that regularly serve 25 or more people or have at least 15 year-round service connections and that use ground water as a drinking water source. EPA does not regulate private wells. Aeration of water to promote the release of radon is very effective and one of the more affordable water treatment technologies available.

The 1996 Safe Drinking Water Act Amendments required EPA to establish several new health-based drinking water regulations. The first of these, announced by President Clinton in December 1998, was for cryptosporidium and other disease-causing microbes and for potentially harmful byproducts of the water treatment process. The proposal for radon is the second of these new regulations. EPA will be developing new drinking water regulations for arsenic early next year.

EPA is soliciting formal comment by publishing the proposed regulations in the Federal Register for review for 60 days. The regulations are scheduled to be finalised in August 2000.

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