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The first phase of the Southwest Wisconsin Groundwater and Geology Study of Grant, Iowa and Lafayette counties was recently completed. The study’s researchers reached their first objective – to assess the extent of well contamination in the three counties.

The second and final round of groundwater sampling was collected in mid-April. Samples were collected from 539 randomly selected private wells, a different group than the first round of sampling that occurred in November 2018.

Of wells tested in April 27 percent didn’t meet health standards for total coliform, Escherichia coli or nitrate. Of the samples 16 percent were positive for total coliform and 2 percent were positive for E. coli.

Fifteen percent of samples exceeded the 10-parts-per-million health threshold for nitrate-nitrogen. The most significant sample result was 67 parts per million; the median was 3 parts per million.

The percentage of wells positive for total coliform is less than the November 2018 sampling event, when 34 percent of wells tested positive. Nitrate and E. coli results are similar to November, when 16 percent of samples exceeded the threshold for nitrate and 4 percent were positive for E. coli.

“Finding fewer coliform detections in wells tested in early spring is consistent with other statewide surveys,” said Ken Bradbury, director of the Wisconsin Geological and Natural History Survey and state geologist. “This may be because bacteria die during winter. There also are fewer contamination sources on the land surface in winter.”

Mark Borchardt, a microbiologist with the U.S. Department of Agriculture’s Agricultural Research Service, said, “We now have a solid assessment of private-well contamination in southwest Wisconsin based on a large representative sample of wells.”

Wells were randomly selected to minimize bias. Of private wells in the three counties 8 percent were tested. The “snapshot” approach of collecting all samples at about the same time gave researchers greater capability to identify factors related to well contamination.

“We can no longer say we don’t know the extent of the problem,” said Lynda Schweikert, administrator of the Grant County Conservation, Sanitation and Zoning Department. “Now we’re asking about the causes of contamination.”

The next research steps will be biological testing of selected wells to distinguish human versus livestock microorganisms in well water. The researchers also will conduct geologic studies and analyze well-construction practices in the three-county region. They plan to determine correlations between water quality, geology and well construction.

Private-well owners are advised to test wells annually. Residents can contact county-health departments in Iowa, Grant or Lafayette counties for information on testing, costs and certified laboratories. The Wisconsin DNR also provides information and advice for well owners.

The study was initiated by Grant, Iowa and Lafayette counties in collaboration with researchers from the USDA, the Wisconsin Geological and Natural History Survey, the University of Wisconsin-Extension and the U.S. Geology Survey. The study is supported by the counties and agencies involved as well as other organizations such as the Lafayette Agricultural Stewardship Alliance and the Iowa County Uplands Farmer-led Watershed Group.

Visit dnr.wi.gov/topic/Wells for more information.

The article was written by the University of Wisconsin-Madison Division of Extension with input from Ken Bradbury of the Wisconsin Geological and Natural History Survey, and Mark Borchardt of the U.S. Department of Agriculture’s Agricultural Research Service.