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HELENA (AP) - Trace amounts of nearly two dozen contaminants _ including antibiotics, herbicides and sunscreen _ were found in a sampling of 38 Helena Valley water wells by state and local officials.

The study, believed to be the first of its kind in Montana, was a cooperative effort between the state Department of Environmental Quality, the Montana Bureau of Mines and Geology, and the City-County Health Department.

A range of pharmaceuticals and personal care products were found in the wells between the North Hills and Montana City. Using data collected last year, antibiotics, bug spray, caffeine, ibuprofen, steroids and lotion also were found in all but three of the public and private wells tested.

The study's authors couldn't be reached for comment Friday, but City-County Health Department watershed expert Jim Wilbur said the contaminants were found at very low concentrations and shouldn't cause undue alarm.

The results do, however, demonstrate people's impact on the water they use, he said.

"These chemicals are pervasive in our society," Wilbur said. "What we flush down our septic systems … does not disappear. To us, it's confirmation that humans are having an impact on our groundwater."

The report comes during an ongoing debate about extending city wastewater services to the Helena Valley.

County Administrator Ron Alles said Friday the county won't likely be able to build a proposed four-mile, $4 million sewer extension to Sierra Road, but can help existing neighborhoods hook up with city approval. The line was proposed to replace some aging wastewater systems.

Some wells in the water study were chosen randomly, while others were picked due to suspected contamination. The well locations were roughly concentrated north of East Helena, west of Helena and in the central and north Helena Valley areas, a map in the study shows.

"Every time someone gets in the shower and washes off sunscreen, it makes its way into the groundwater," said Kathy Moore, administrator of the Lewis and Clark County Water Quality Protection District. "When thousands of people are using sunscreen every day, and then washing it off into the groundwater, the impact adds up quickly."

Pharmaceuticals and personal care products have likely been in the groundwater for some time, she said, but the county hadn't had the equipment to test for them.