Lee Bergquist | Milwaukee Journal Sentinel

This story from Aug. 1 has been updated to clarify that the wells in this study were randomly selected from previously tested wells that were found to be contaminated.

As worries grow over contamination of rural drinking water, a new study of private wells in southwestern Wisconsin — those previously flagged as tainted — found the overwhelming majority were contaminated with fecal matter.

Results from the independent study released on Thursday showed that 32 of 35 wells — or 91% — contained fecal matter from humans or livestock.

Also detected in some of the wells in April during testing were illness-causing pathogens such as salmonella, rotavirus and cryptosporidium.

The 35 wells were randomly selected from wells that in earlier rounds of testing were found to be contaminated with coliform bacteria or nitrate that exceeded the acceptable limit in drinking water.

The results from Grant, Iowa and Lafayette counties are the latest in a series of tests showing an array of problems with well water in the three counties.

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These findings, and test results elsewhere, highlight the potential vulnerability of Wisconsin groundwater from agricultural practices and defective septic systems.

About one-quarter of the state’s residents get their water from more than 800,000 private wells, according to state figures.

“As a researcher of groundwater for 25 years now, I continue to be amazed by the level of fecal contamination in Wisconsin groundwater,” said Mark Borchardt, a research microbiologist for the U.S. Agricultural Research Service.

The work was conducted by Borchardt, others in his agency and the Wisconsin Geological and Natural History Survey. Financial support came from the counties, the agencies and local groups. More testing in the counties is expected, with the next round in early August.

Groundwater attracts attention

On Wednesday, Democratic Gov. Tony Evers proposed new regulations aimed at farmers and their use of manure and fertilizer. The regulations would target regions that are susceptible to nitrates — another source of groundwater pollution.

Those measures will need approval by the Republican-controlled Legislature.

In the meantime, underscoring the heightened attention to groundwater, Assembly Speaker Robin Vos, R-Rochester, created a water quality task force in February and has been holding hearings across the state.

Vos formed the legislative task force after Borchardt’s group released the results from an initial round of testing in the three counties.

In that first round, 42% of 301 wells had evidence of total coliform or nitrate that exceeded the state's health standard. In a second round of 539 wells, 27% turned up total coliform or nitrate above the state standard.

The region draws groundwater from fractured dolomite, a type of limestone, which can lead to contaminants seeping into water-bearing rock.

In the latest study, tests found contamination from human waste and septic systems in 30 of the 35 wells.

Contamination in 17 of the wells was from cattle and five from swine. In some wells, the researchers found a mix of human and animal waste.

In addition, 13 of the wells were found to have pathogenic organisms that could make people sick. The results were sent to homeowners this week.

“I would say that there is widespread fecal contamination in the counties, but concentrations tend to be on the low side,” Borchardt said.

The wells containing pathogens that could sicken people are worrisome, he said. But overall, the results “are a cause for concern, but not a cause for alarm.”

While more contamination came from defective septic systems than from livestock, Borchardt said he expected proportions to change in future rounds of testing.

Another study by Borchardt in cattle-intensive Kewaunee County in the northeast in 2016 and 2017 also showed widespread well contamination. The sources came from cattle — especially during wet conditions when water was flowing into aquifers — and from ineffective septic systems.

The results in southwestern Wisconsin show that “what we are currently doing is not working,” said Lynda Schweikert, director of conservation, sanitation and zoning in Grant County.

“We can’t point fingers at just farmers or just septics — we know all of it is having an impact.”

Scott Laeser, director of water programs for Clean Wisconsin, an environmental group, agreed.

“What we shouldn’t do is get bogged down in finger-pointing,” Laeser said. “We need to start focusing on what we are going to do about it.”

Jamie Mara, a spokesman for the Wisconsin Dairy Business Association, said that “these latest findings in southwestern Wisconsin confirm again what research elsewhere has shown — there are multiple sources of contamination.

“That’s why achieving long-lasting solutions is going to require a comprehensive approach.”