Radon can be found in ground water sources of drinking water (rather than surface waters, such as rivers, lakes and streams) in some parts of the United States. 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. Most of the risk from radon in drinking water (nearly 90 percent) comes from breathing radon released to indoor air from household water uses.
Compared to radon entering the home through soil, radon entering the home through water will in most cases be a small source of risk. radon gas can enter the home through well water. It can be released into the air you breathe when water is used for showering and other household uses.
Radon problems in water can be readily fixed. The most effective treatment is to remove radon from the water before it enters the home. This is called point-of- entry treatment. Treatment at your water tap is called point- of-use treatment. Unfortunately, point-of-use treatment will not reduce most of the inhalation risk from most of the inhalation risk from radon.
The EPA published draft regulations for a radon standard in drinking water in October 1999. The proposed regulation would provide two options to states and water systems for reducing public health risks from radon in both drinking water and indoor air, a unique multimedia framework authorized and outlined in the l996 amendments to the Safe Drinking Water Act.
Under the first option, states can choose to develop enhanced state programs addressing 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 programs 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.
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 EPA has missed Congress's deadline of October 2000 to finalize the proposed drinking water standard. See EPA's web site for additional information http://www.epa.gov/iaq/radon/rnwater.html
Currently there are no laboratories certified to perform radon in water analysis and no standard for radon in water, whether private wells or community water systems.
In Virginia only a few water systems have been tested for radon in water, and there have been systems reported to have exceeded the proposed EPA standard.
In general 10,000 pCi/L of radon in water will raise the radon levels in air by 1 pCi/L. This called a transfer coefficient and is 10,000:1 for radon. Inhalation of radon is the primary route of radiation exposure to humans.
Radiological Health Program | James Madison Building, 7th Floor | 109 Governor Street, Room 730 | Richmond, VA 23219 | Telephone (804) 864-8150 | Fax: (804) 864-8155