A study to map radioactivity in groundwater may start this month with geologists returning to the Simpsonville, S.C., area where traces of uranium and radium were found in well water in 2001.
Later testing found trace radioactivity in public wells near lakes Keowee and Jocassee.
The Department of Health and Environmental Control discovered traces of radium in wells in Lexington County earlier this summer.
The naturally occurring elements are slightly above background levels.
The U.S. Environmental Protection Agency says levels are probably not an immediate health threat, but they may slightly elevate a person's risk of some cancers over a lifetime of drinking the affected water.
The agency is helping to pay for a testing and mapping project led by University of South Carolina geologist Tom Temples.
"Very few people in the Upstate and even the Lowcountry are on a public water supply," Temples said. "They don't know, unless they've gotten it tested, what's in (their well water)."