The data from a study of well contamination in Kewaunee County seems to show relationships between depth of soil and the likelihood of contaminated groundwater, especially when manure is applied to farm fields during periods when the water table is recharging.

That conclusion is among the takeaways from a Wednesday night presentation by two of the lead scientists in the two-year study for a crowd of about 200 people at the Kewaunee County Fairgrounds in Luxemburg.

Maueen Muldoon

UW-Oshkosh geologist Maureen Muldoon explains how contaminants can seep quickly through fractures in karst bedrock into groundwater.

Maureen Muldoon, geologist with the University of Wisconsin-Oshkosh, gave an overview of the shallow soil over the fractured karst topography of northern Kewaunee County and Door County, which are part of the western edge of the Niagara Escarpment.

Mark Borchardt of the USDA’s Agricultural Research Service then presented data from the random sampling of 621 private wells in the county. About 208 of those wells showed contamination from bacteria or high nitrate levels, and a review of the pathogens in the contaminated wells showed levels well above the state average. There was evidence of both bovine and human waste in the affected wells.

The levels were especially high in areas with 5 feet or less of soil over bedrock, and to only a slightly lesser extent when the depth to bedrock was 5-20 feet.

Mark Borchardt

USDA researcher Mark Borchardt said levels of coliform, E. coli and nitrates in some Kewaunee County wells raised concerns.

The spring and fall, where manure spreading on farm fields is most prevalent, is also a time when groundwater levels are rising, or recharging, because of snow melt and rain, and the contamination was especially dramatic during those times of year in the shallowest soil.

“What we think happens is that during recharge after manure’s applied, that’s when the groundwater contamination with bovine manure goes up; it goes down again in the summer … and then in the fall after manure’s applied again, it probably goes up again,” Borchardt said. “This is our hypothesis; this is our working model of what we think is happening.”

The next step is to analyze the data to determine the association between fecal sources, pathogen types and pathogen concentrations and well construction, hydrologeological and environmental variables.

The research will eventually be published in at least three articles for technical scientific journals.

Below is the information from two key slides in the scientific team’s PowerPoint presentation.

Muldoon and Borchardt

Mark Borchardt and Maureen Muldoon, at the microphone, answer questions from a crowd who came to hear the results of their Kewaunee County well contamination study.

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The bullet point conclusions of an ongoing study of well contamination in Kewaunee County:

+ On a countywide basis 26% to 28% of private wells are positive for total coliforms, E. coli or nitrate.

+ At depths to bedrock less than 20 feet, contamination rates generally exceed statewide averages.

+ Well contamination results from both human and bovine fecal sources.

+ The primary source of fecal contamination, bovine or human, appears to vary with groundwater recharge and the timing of manure application.

+ Wells are contaminated with pathogens of significant concern: Salmonella, EHEC, Cryptosporidium, rotavirus.

+ We estimate contaminated private wells are responsible each year in Kewaunee County for 140 people and 1,700 calves infected with Cryptosporidium parvum.


Researchers studying the issue recommended several steps for county residents to counter the possibility of contamination:

+ Water treatment by reverse osmosis or ultraviolet light.

+ Maintain water treatment equipment.

+ Be aware of heavy rainfall and snowmelt as times when wells are most vulnerable to contamination.

+ Monitor the U.S. Geological Survey monitoring well in Kewaunee County for groundwater recharge.

+ Be careful to avoid contaminated drinking water exposure to young children, elderly, and people with altered immune systems.

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