Prepared by:
Robert Leker
Extension Radon Specialist

Published by: North Carolina Cooperative Extension Service

Publication Number: HE-396

Last Electronic Revision: March 1996 (JWM)

Radon is a naturally occurring radioactive element found in most groundwater in North Carolina.

In water, radon is measured in picocuries per liter (pCi/L). Ten thousand pCi/L in water translates to about 1 pCi/L in air. The current "action level" for airborne radon is 4 pCi/L. The U.S. Environmental Protection Agency (EPA) recommends that action be taken to lower airborne radon if it exceeds 4 pCi/L in your home. While there are no EPA standards for radon in water now, a maximum contaminant level (MCL) of 300 pCi/L for public water supplies is being considered.

Based on an EPA pilot study, the average waterborne radon level in public groundwater supplies is 353 pCi/L. This same study showed the average for North Carolina groundwater was 545 pCi/L, somewhat above the national average.

Although these averages seem high compared to the EPA's proposed standard of 300 pCi/L, the average of 545 pCi/L reflects the fact that there were some water supplies with high radon levels, which made this average higher than most of the public groundwater radon levels sampled in North Carolina. If the data were written on paper, ranked from lowest to highest, the tested radon level in the center would be 48 pCi/l. This is called the "geometric mean," which is different than the average that is usually used with most data.

Radon
(Radon 222) is a naturally occurring radioactive element measured in picocuries per liter (pCi/L). Radon is produced during the radioactive decay process of uranium that has been in the earth's crust since the earth was formed. In water, radon is measured in picocuries per liter (pCi/L). A picocurie is 0.037 radioactive disintegrations per second. The EPA estimates that 10,000 pCi/L in water translates to about 1 pCi/L in air.

Concentrations vary widely in North Carolina groundwater. Public groundwater supplies seem to have the highest radon levels where the water moves through granites in the piedmont. The highest readings there have been over 10,000 pCi/L. The lowest concentrations occur in the coastal plain region, where many readings are below 100 pCi/L. Concentrations from about 500 to 10,000 pCi/L occur in groundwater water samples drawn from metamorphic rocks, such as the gneisses and schists found in the piedmont and mountain regions.

A high concentration of radon in the groundwater in your area does not necessarily mean that there will be a high concentration of radon in your drinking water. Radon escapes harmlessly into the air when water is being treated for use in a municipal system. Also, radon decays into other substances over time while the water is being stored. Municipal systems that use surface water—a lake or a river—instead of groundwater will probably have low waterborne radon levels.

High levels of waterborne radon tend to occur in homes on an individual well or a community well system (serving up to about 100 homes) if the groundwater has a high level of radon.

The largest releases of waterborne radon in your home come from those activities and appliances that spray or agitate water, such as taking showers and washing dishes or clothes.

Drinking water that contains radon is not believed to cause a significant health risk, but a high airborne radon level is linked to increased risk of lung cancer.

Approximately one out of every 10 homes in North Carolina has an airborne radon level above 4 pCi/L. Radon in water contributes to the airborne radon level in some of these homes, adding to the airborne radon that enters the house as a soil gas. Over a long period, airborne levels of radon above 4 pCi/L may increase your family's risk of lung cancer.

Test your home for radon. Test the air level first. If the level is above 4 pCi/L and you get your water from a private well system, you may want to test your water for radon.

To test for radon, draw a water sample from an indoor faucet after the removing the aerator. Collect the sample in a special vial supplied by the testing lab. Take the sample after running the cold water at a slow but steady rate. Then send the sample to the lab for analysis.

If initial tests indicate a problem, use follow- up tests to verify the results. If follow-up tests show that a substantial portion of the radon in your home comes from your household water supply, consider taking some action to lower radon levels in your water supply.

Good ventilation of bathroom, laundry, and kitchen areas may be enough to prevent the buildup of airborne radon coming from water.

If this is not effective, consider a granular activated carbon filtration system or an aeration system.

Granular activated carbon (GAC) filter systems have been very effective at lowering water- borne radon levels, but the radioactivity that builds up in the filter bed may be of some concern. Install GAC systems only outside of your home.

Aeration systems are also effective and do not accumulate radioactivity. Aeration systems mix the water with air in an outside-vented chamber. After aeration, the water is piped into the house free of radon. Aeration systems require periodic cleaning to remove particulates that come from minerals in the water.

Since 10,000 pCi/L in water translates to about 1 pCi/L in air, relatively few people have to worry about the health risks posed by water- borne radon.

Everyone should test for airborne radon levels in their homes. The test is inexpensive and you can do it yourself. If you do find that you have a level higher than 4 pCi/L, and your water comes from a private well, you may want to test that water for radon. If radon levels in your water are 40,000 pCi/L or greater, action may be taken to lower the waterborne radon levels.

Contact the extension center in your county or the North Carolina Division of Radiation Protection in Raleigh for more information on radon testing and removal systems.

Loomis, Dana P. 1987. "Radon-222 Concentration and Aquifer Lithology in North Carolina," 1987. Groundwater Monitoring Review, Volume 7, pp. 33- 39.

Nationwide Occurrence of Radon and Other Natural Radioactivity in Public Water Supplies. 1985. USEPA 520/5-85-008. U.S. Environmental Protection Agency, Washington, D.C. Radon Reduction Techniques for Detached Houses: Technical Guidance. 1988. USEPA/625/5-87/019. U.S. Environmental Protection Agency, Washing- ton, D.C.

Sasser, M. Kent and Watson, J.E. Jr. 1977. "An Evaluation of the Radon Concentration in North Carolina Groundwater Supplies." Health Physics, Volume 34, pp. 667-671.

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

HE-396