A multi-agency testing of 34 private wells in southwest Wisconsin in August 2019 found that 73% contained microbes indicating the presence of fecal material.

A recent round of water testing in southwestern Wisconsin confirms that humans and livestock manure have contaminated wells, some of which contain pathogens capable of causing disease.

Of 34 private wells that previously tested positive for contamination, 25 — or 73% — contained microbes indicating the presence of human, bovine or porcine fecal material. Meanwhile, 19 of the wells contained pathogens, such as norovirus, rotavirus and salmonella.

“Almost all the pathogens that we detected are capable of infecting people and cattle,” said Joel Stokdyk, a biologist with U.S. Geological Survey, one of the agencies overseeing a groundwater quality study.


Staff in Grant, Iowa and Lafayette counties — where testing is being conducted — along with scientists from the U.S. Department of Agriculture and Wisconsin Geological and Natural History Survey are assisting with the water quality study.

The wells are a subset of 840 in the counties that were randomly selected for testing.

Samples indicated that 42% of 301 wells tested in November 2018 were contaminated with coliform bacteria or nitrates in excess of federal standards. An April sample of 539 wells found that 27% were contaminated.

To ascertain potential sources, researchers returned to the contaminated wells for further analysis. One sampling indicated that 91% of wells were contaminated with waste of multiple origins.

The latest results confirm the findings.

“The longstanding purpose of this was to help determine what the sources of contamination are — to determine that it’s just not one thing,” said State Geologist Ken Bradbury.

Because the wells are among those that already tested positive for coliform bacteria or high nitrates, the rates of contamination cannot be generalized to the region at large.

A press release issued by the counties stated, “It’s too soon to assess which contamination source is more prevalent since they can vary seasonally” and the “percentage of wells that test positive is also expected to differ as weather and land use change over time.”

The data also do not quantify the health risks posed by the pathogens, which vary depending on the amount of pathogen present, the amount of contaminated water consumed and the health of the animal or human drinking the water, according to Stokdyk.

The data release follows a controversial proposal in which Lafayette County officials — frustrated with recent reporting of study findings — threatened to prosecute journalists who reported on findings without quoting county news releases verbatim. The county’s board of supervisors accused media outlets, including the Associated Press and Milwaukee Journal Sentinel, of reporting 91% of the entire region’s wells were contaminated.

Amid ensuing criticism, the board declined to act on the measure.

Two more rounds of well sampling are scheduled through the spring. A final report is expected for release by the end of 2020.