BOULDER -- A government study found elevated levels of uranium in a sample of Jefferson County wells, according to a report released at Tuesday's county commission meeting.

The U.S. Geological Survey found that five wells, or 12 percent, of the 40 sample wells tested in Jefferson County had uranium concentrations exceeding U.S. drinking water standards.

And 16 wells showed radon concentrations exceeding proposed drinking water standards.

The USGS reported any water quality problems they found to the well owners.

Most of the problem wells were within the Boulder Batholith, a geological formation that extends under 30 percent of Jefferson County. The formation contains igneous rocks known to contain uranium.

The USGS cooperated with the county and Jefferson Valley Conservation District to conduct the five-month, $50,000 study that tested the sample wells, which were dispersed across the county.

It was the first such USGS county study of uranium in groundwater in Montana, said USGS scientist Rod Caldwell.

A lifetime exposure to elevated levels of radioactive elements in drinking water can increase the risk of cancer and cause kidney damage, according to the US Environmental Protection Agency.

Radon and uranium in water are generally colorless, odorless and tasteless, according to the USGS report. However, radioactive elements can be detected by water-quality tests for heavy metals.

The intent of the study is to raise public awareness of potential water-quality problems, Caldwell said.

Homeowners can have their wells independently tested for heavy metals.

Effective treatments are available to reduce concentrations of uranium and other radioactive elements in private wells, he said. Residents should consider treatment options before digging another well.

For more information about testing well water, Jefferson County residents can call the county sanitarian at 442-4126 or the Montana Department of Public Health and Human Services Environmental Laboratory at 444-2642 or a private laboratory.

Information on EPA drinking water standards and water quality is available at the Safe Drinking Water Hotline 1-800-426-4791.

Groundwater is the sole source of drinking water in the study area, Caldwell said. Over 3,000 domestic wells supply water to more than half the county's population.

Thirty of the sample wells were randomly chosen and 10 were in areas known to have had previous uranium concentration problems.

Caldwell urged additional study.

"We have just scratched the surface," he said. "Our focus was uranium."

However, test results indicate that other radioactive elements are also present in the groundwater.

Reporter Marga Lincoln: 447-4074 or marga.lincoln@helenair.com