Radon is a radioactive gas that is formed by the decay of uranium in rocks and soil. As water passes through rock and soil, radon is dissolved into ground water. Radon is naturally found at varying concentrations in wells used for drinking water. Radon gas from rock and soil can enter homes through cracks in concrete walls and floors. Radon can also enter indoor air of homes from drinking water during showering, dish washing, etc. Radon in drinking water transfers to air at a conversion rate of 10,000 to 1. Thus, 10,000 picocuries/liter of radon in water will create an indoor-air radon concentration of 1 picocurie/liter. Picocuries are a measure of radioactivity. The international unit of radioactivity, becquerel, is equal to approximately 27 picocuries. There is concern about cancer and other health effects from inhaling or ingesting high concentrations of radon.

A recent National Research Council (NRC) study, commissioned by Congress, concluded that radon in household water poses few risks to health. The NRC study found that soil underneath homes was a much more significant source of radon. According to the study, the background concentration (outside air) of radon is 0.4 picocuries/liter (pCi/l) of air. Radon gas can accumulate at much higher levels inside homes. The Environmental Protection Agency recommends that actions be taken to reduce radon when the airborne concentration exceeds 4 pCi/l. The NRC study also reported that smokers have a greatly increased risk of lung cancer when exposed to radon gas.

The National Research Council and the American Water Works Association have urged the EPA to set a maximum contaminant level (MCL) of 4000 pico curies of radon per liter ( approximately 150 becquerel per liter ) in drinking water. In 1991, the EPA proposed a radon MCL of 300 picocuries per liter (pCi/l) but this was not passed into law. The EPA will propose a new MCL by August, 1999. The EPA will also set an alternative MCL, possibly at 4000 pCi/l, that would be accompanied by programs to decrease radon in indoor air. Water treatment methods for reducing radon /include aeration and granular activated carbon.

The average radon levels for Dayton’s water are 100 pCi/liter (4 becquerel) for the Ottawa Water Treatment Plant and 105 pCi/liter for the Miami Water Treatment Plant. The average for samples collected in the distribution system is less than 70 pCi/liter. Across the United States the concentration of radon in municipal well water ranges from less than 100 to greater than 4000 pCi/l.

The E.P.A. has established maximum contaminant levels for other radioactive substances in drinking water; radium 224, radium 226, uranium, alpha emitters and beta particles. These substances are usually not detected in Dayton’s water. Alpha Emitters, from the erosion of natural geological deposits, were detected at 4.3 pCi/l in 1998. The MCL (highest level allowed) is 15 pCi/l.

For more information, contact the City of Dayton Division of Water Supply and Treatment between 7 a.m. and 3:30 p.m. at 3330-6030. Martha Schwendeman is the manager of this division.