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The Southwest Wisconsin Groundwater and Geology Study of Grant, Iowa and Lafayette counties is halfway through its second phase to identify fecal sources of contamination in private wells. The study’s latest phase found fecal contamination in 27 of the 34 private wells sampled.

The 34 wells were selected at random in November 2019 after earlier sampling in the study found them to be contaminated with coliform bacteria or with levels of nitrate exceeding the drinking-water standard. Samples for specific viruses and bacteria indicate fecal contamination from human wastewater or livestock manure. Not all of the viruses and bacteria are capable of causing illness.

The scientists found evidence of both human and livestock sources for the contamination. In 16 of the 34 wells the scientists found pathogens associated with gastrointestinal illness in humans. But the scientists haven’t calculated the health risk for the results, which vary based on the specific pathogen, its concentration and the health of the person who drinks the water.

The study has been designed for sampling water in all four seasons since contaminant abundance can vary seasonally. The percentage of wells that test positive is also expected to differ because weather and land use change through time. The percentage of contaminated wells from the sampling event doesn't represent the entire region because they were chosen from wells already shown earlier in the study to be contaminated.

The researchers will randomly select different wells for future sampling rounds and will release results when they’re available. The study team will also look for correlations between water quality, geology and well construction. The study’s final report is planned to be complete in early 2021.

The study began in late 2018 with the goal of assessing the quality of drinking-water sources from private wells in southwest Wisconsin and determining probable sources of contamination found. The study was initiated by Grant, Iowa and Lafayette counties in collaboration with researchers from the U.S. Department of Agriculture, the University of Wisconsin-Division of Extension-Wisconsin Geological and Natural History Survey, and the U.S. Geological Survey. Support for the study comes from the counties and agencies involved, the Lafayette Ag Stewardship Alliance, the Iowa County Uplands Watershed Group and donations from Lafayette County citizens. Visit wgnhs.wisc.edu for more information.