A report out Thursday said 42 percent of 301 random wells in southwest Wisconsin were contaminated.
Some of that can be blamed on farm waste or runoff, while the makeup of soil in rural areas also can make contamination easier.
Cities such as La Crosse, however, have more control over water quality than farm areas do.
The manager of La Crosse’s water utility, Bernie Lenz, said La Crosse tap water is tested 60 times a month and goes through processing to keep it clean.
“We haven’t had a positive bacterial test since 2015 and that was as a result of maintenance work we did on a well,” Lenz said.
In northern areas of La Crosse County, however, a well-water alert was issued two years ago because of excess bacteria and nitrates in some wells.
Lenz looks at the differences between the soil in La Crosse and what might be found in many farm areas.
“Fine soils over bedrock where the contaminant can get through that soil, into the bedrock and directly into the wells,” Lenz said. “We have a 170 feet of sand to the wells, so a lot of that stuff is filtered out, cleaned out in that.”
Assembly Speaker Robin Vos is forming a water-quality task force, following the water quality study.
The contaminated wells were found in Iowa, Grant and Lafayette counties, and exceeded federal standards for bacteria that can come from animal or human waste or for a toxic fertilizer residue.
The survey was conducted in November by the Wisconsin Geological and Natural History Survey, the U.S. Department of Agriculture and the U.S. Geological Survey.