Eastern radon ranked by region.

Taking a tip from modern mail-sorting methods, two geologists are zipping along in their assessment of radon levels along the Eastern Seaboard, first in indoor air and most recently in drinking water.

George W. Mushrush and Douglas G. Mose of George Mason University in Fairfax, Va., compiled 71,000 indoor radon measurements gathered by five private testing companies. Then, using zip codes, they plotted the measurements by geologic province to show the level of radon risk, Mose says.

The densely populated Piedmont province, with its 500-million-year-old rock, and the Highlands province, with billion-year-old granites and gneisses, generate the most radon, especially where glacial deposits do not cover the bedrock, the team reports. These provinces include New York's Dutchess County and the New Jersey counties of Hunterdon, Morris and Warren. There, indoor radon concentrations averaged about four times higher than the level above which the Environmental Protection Agency recommends corrective action (4 picocuries per liter), says Mose. Coastal provinces had the lowest radon levels in the survey, he adds.

To gauge the risks of water-borne radon, Mose and Mushrush sent health questionnaires to Virginia and Maryland residents who had participated in previous studies of radon in indoor air. They also collected water samples from the roughly 250 homes with private wells in this group.

In 234 of the 250 well-water samples they detected radon levels exceeding 2,500 picocuries per liter. On the questionnaires, 5 percent of the participants living in these homes reported cancer diagnoses, compared with 2 percent of those whose well water had low radon levels, Mose says.

In July, EPA proposed setting a maximum acceptable level of 300 picocuries per liter for radon in wter supplies. The agency is seeking public comment on the recommendation through mid-October.