HELENA — Radioactive elements have been detected in all of the 128 residential wells that were tested in a recent seven-county study in south-central Montana, with 49 wells -- 29 percent of those sampled -- exceeding drinking water standards.
All the wells tested in Lewis and Clark, Silver Bow, Powell, Madison, Deer Lodge and Broadwater counties were sampled for uranium, with 18 showing results above the maximum contaminant levels (MCL) for municipal drinking water of 30 micrograms per liter (ug/L). The highest concentration was 1,130 ug/L.
Of 127 wells sampled for radon, 34 were above the 50 ug/L MCL, with the highest concentration at 45,000. Other radioactive constituents, including alpha and beta radioactivity, were found at various levels.
According to the Environmental Protection Agency, a lifetime exposure to elevated levels of radioactive elements in drinking water can increase the risk of cancer and cause kidney damage. Both radon and uranium in water are generally colorless, odorless and tasteless.
"If you drink water with 30 parts per billion of uranium, (the MCL) at 2 liters per day for 70 years, you may have a one in 10,000 chance of developing cancer from that source," Rod Caldwell, a USGS scientist, said on Tuesday. "But the question is if you're drinking water with everything in it that's below the drinking water standards, but they have all of those (radioactive constituents) in it, what does that mean?"
The wells were tested by the U.S. Geological Survey after rumors circulated in 2007 of elevated levels of uranium in a north Jefferson County residential well. When that well's water showed uranium at 2,000 parts per billion, the USGS and the county decided that the testing should be expanded.
"(The original well users) were drinking 60 times the drinking water standard and didn't find out for 20 years. They had some health issues," Caldwell said. "My gut reaction was to wonder how widespread this is and whether there are other wells with this kind of concentration."
Additional sampling of 40 more wells in Jefferson County that year found that five wells, or 12 percent, had uranium concentrations exceeding U.S. drinking water standards. Sixteen wells showed radon concentrations exceeding drinking water standards.
"Our 2007 study lead to more questions, like whether concentrations vary over time; can we determine where we are more likely to find elevated concentrations; and if you have this, what can be done about it?" Caldwell said.
That led them to expand the sampling in 2009 and 2010 in the seven counties. The preliminary results of the study were presented to the Jefferson County Commission on Tuesday.
"We want to make sure the public is aware of the numbers," Caldwell said, adding that a final report, including interpretation of the results, will be available in about a year. Individual homeowners were made aware of their well water sampling results.
The radioactive elements, also known as radionuclides, are unstable trace elements that naturally occur in rocks, soil and groundwater. In particular, the Boulder Batholith granitic formation is well-known for its uranium, with some mining of the element there in the 1950s.
Caldwell said that as uranium breaks down over billions of years, it emits radioactive constituents including alpha and beta particles, radon, and radium 226 and 228, all of which decay at various rates to a stable form of lead. The constituents are measured in picocuries, with the standards being presented as a picocurie per liter format.
According to the study, 38 out of 58 wells tested in the Boulder Batholith had elevated levels of the radioactive constituents that were greater than drinking water standards. In addition, 11 out of 70 tested in other rock formations also were elevated.
Caldwell said there didn't seem to be any particular clusters of contaminated water. He added that it could be more widespread, since testing the radionuclides is a fairly new procedure.
Megan Bullock with the Jefferson County Environmental Health division said that sampling is available through the state and costs about $225.
She added that the good news is that simple reverse osmosis water filters, which were tested as part of the study, seem to remove the radioactive constituents.
"You can pretty much go to any home improvement store, buy a reverse osmosis system and put it on," Bullock said. "It was remarkable how well the units performed.
Costs for those systems range in price from $147 to $3,000, and while she didn't want to endorse any particular brand, she noted that the mid-range models seemed to work best.