A study of contaminated wells in three southwestern Wisconsin counties has found human waste is more often the cause than animal manure.
Researchers with the Southwest Wisconsin Groundwater and Geology Study — or SWIGG — recently completed a fourth round of tests on private wells in Grant, Iowa and Lafayette counties that had shown previous signs of contamination.
Of the 138 wells tested, three-quarters had some sort of fecal microbes: 46% had viruses or bacteria associated with human waste and 33% had material from cow or pig manure. Some had both human and animal material.
“We are looking into possible reasons for this but do not have an explanation at this point,” said state geologist Ken Bradbury, one of the researchers leading the study.
Just under half the wells tested positive for pathogens associated with stomach illness.
The results differ slightly from a similar study done in Kewaunee County, where contamination from human and animal waste was roughly equal, said Mark Borchardt, a research microbiologist with the U.S. Department of Agriculture.
Results of the four rounds of sampling show contamination levels were highest in April and November, which Borschardt said correlates with seasonal manure spreading and natural groundwater recharge.
Researchers have identified a number of potential factors, including differences in agricultural practices or soil types, that will be explored in the final report, which is due to be published next year, but Borchardt warns they will not be able to say definitively.
They have not calculated the health risks, which they say depend on multiple factors, including the specific pathogen, its concentration and the health of someone drinking the water.
The wells were randomly selected from a pool of wells that were previously shown to have coliform bacteria or nitrate levels above the drinking water standard.
Like other parts of Wisconsin, the southwestern part of the state has areas where porous bedrock means manure spread on farm fields and human waste from private septic systems can seep into the aquifers tapped for drinking water.
Nitrate — from fertilizer, animal and human waste — is the most common contaminant in Wisconsin groundwater and can be especially hazardous to pregnant women and infants.
In Grant, Iowa and Lafayette counties, some 44% of people get their water from private wells. Across the state, some 25% of residents rely on tap water that comes from private wells.
SWIGG researchers are now studying the data to find connections between water quality, geology and well construction to guide public policy decisions on things like the density of septic systems in an area or how far livestock facilities should be from a property line.
“You could get a nice paper just with this,” Borschardt said. “We want to take it a step further and identify these risk factors, which is the same thing in my mind as identifying potential solutions.”
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