Rock County residents are at risk of unsafe drinking water as nitrate levels in groundwater continue to rise, said Rick Wietersen, environmental health director at the Rock County Public Health Department.

More than 30 percent of private wells exceed the health advisory level for nitrates, according to the health department.

Nitrate contamination has become a top priority for the county, said Josh Smith, county administrator.

The county formed the Nitrate Work Group in 2016 to plan a multiyear study on contamination, Smith said. The study would identify funding for further action.

Nitrate contamination is one of the county’s public safety issues that would face funding cuts if the town of Beloit incorporates into a village, according to a county board resolution opposing the town’s incorporation.

Rock County would lose $1.08 million annually if the town incorporates, according to the resolution. The county board is scheduled to vote on the resolution Thursday night.

The health department has monitored nitrate levels for about 20 years, Wietersen said. Levels have increased gradually over time, to where the county believes a change in land use needs to be implemented.

Nitrates are found naturally in groundwater from the decay of plant materials, Wietersen said. Natural decay accounts for nitrate levels of less than one part per million.

High nitrate levels are caused by fertilizer and manure run-off into groundwater, Wietersen said.

Nitrate levels are considered hazardous at 10 parts per million, Wietersen said. At 20 parts per million, water is considered undrinkable.

Blue baby syndrome, a result of lack of oxygen in an infant or fetus, is the leading health concern from nitrate-contaminated water, Wietersen said.

Residents with private wells should test their water regularly for nitrate, Wietersen said.

If nitrate levels climb above 10 parts per million, residents should consider installing water treatment systems, Wietersen said.

The Nitrate Work Group is a partnership between the health department, county land conservation department, county planning department, UW Extension and UW-Whitewater, according to the health department.

All residents in Rock County are affected by rising nitrate levels, Wietersen said.

Rural areas of the county present higher risk for nitrate contamination, according to a map from the health department. Rural land between Janesville and Beloit and some areas of western Rock County show the greatest risk.

Land cover and fertilizer use, septic system nitrate leaching, irrigation and soil properties are the risk factors used to determine areas with the highest risks of contaminated groundwater.

Reporter - Milton, Edgerton, Albany, Brodhead, Evansville, Footville, Orfordville, health

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