Diluting radon's water risk.
The Environmental Protection Agency ordinarily suggests homeowners consider taking corrective action when indoor radon levels exceed 4 pCi/l. Most of the radioactive gas, estimated to cause up to 20,000 U.S. lung-cancer deaths annually, seeps into homes from the soil. But where soil-radon levels are low or groundwater radon levels are exceptionally high, the offgassing of radon from residential water use can represent a family's major background-radiation threst.
That's the case in some Maine homes, where private well-water supplies carry up to 2 million pCi/l radon -- the highest levels recorded in North America. C. Tom Hess at the University of Maine in Orono has just completed a study of water use, ventilation rates and home size to determine how high levels affect whole-house indoor radon concentrations. The results of his 100-home study show that under average conditions, groundwater-radon levels will be diluted 30,000-fold by indoor air.
What's average? A home with 2,000 square feet of floor space, 8-foot ceilings, 250 gallons of water use per day and a total venting of indoor air about once every 1.2 hours. If the house were much lower, the dilution factor might be only 10,000 to 1. Under the opposite extremes, he found dilutions of 100,000 to 1 were possible.
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|Date:||Oct 15, 1988|
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