GREENVILLE (AP) — Uranium commonly is found in geological formations here, but experts say the levels of radon found in Greenville County test wells are unusually high.

"There's radon everywhere," said Dwight Underhill, a professor in the University of South Carolina's school of public health. "But I'm shocked by how high it is in the water. It just stuns me."

Federal environmental officials said last week that concentrations of radon exceeded the recommended limit in all 17 wells tested in the Simpsonville area after elevated levels of uranium were found in the urine of residents there.

When uranium decays in the earth it creates radon, which has been linked to an increased risk for lung cancer.

Finding radon in this region is not a surprise, given the geology, said Tom Temples, a geologist with the University of South Carolina.

"There's a trend of uranium-bearing rock that runs up and down the Appalachians," he said.

The uranium deposits could be the result of faults that crisscross the region, he said.

"Water containing minerals can move up the fault plain and when conditions change," Temples said, "the minerals will precipitate out."

They also could be associated with the type of rock in the region.

"Granite types tend to have uranium," he said, "and there's a fair amount of that along the Eastern province."

Dark shales and sedimentary rocks containing phosphate also are known to have higher than normal uranium content, according to the United States Geological Survey.

But while high concentrations of uranium can mean high levels of radon, Temples said the amount found in the Greenville County was "fairly significant."

The federal Agency for Toxic Substances and Disease Registry (ATSDR) says radon in the water exceeded the limit of 300 picocuries in all 17 wells. The highest amount found was 195,000 picocuries per liter, according to the report.

"I don't know of any that high anywhere near here," Temples said.

EPA officials estimate that radon in drinking water causes about 168 cancer deaths per year nationwide, 89 percent from lung cancer by inhaling radon released from water, and 11 percent from stomach cancer caused by drinking water containing radon.