SOUTHWEST WISCONSIN - 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 began in late 2018 with the goal of assessing the quality of drinking water sources from private wells in southwest Wisconsin and determining the probable sources of any contamination found.

The latest phase of the study found fecal contamination in 27 of the 34 private wells sampled. In November 2019, these 34 wells were selected at random after earlier sampling in this study found them to be contaminated with coliform bacteria or with levels of nitrate above the drinking water standard.

According to the researchers, 12 of 34 wells in the Fall 2019 sampling showed fecal contamination or pathogens from a human source (35 percent); seven of 34 from a cattle source (21 percent); and three from a swine source (nine percent). In addition, 16 of 34 wells tested showed the presence of pathogens (47 percent).

Compare to previous

This compares to the results of the Spring 2019 and Summer 2019 samplings.

In Spring 2019, 30 of 35 wells showed fecal contamination or pathogens from a human source (86 percent); 17 of 34 from a cattle source (49 percent); and five from a swine source (14 percent). In addition, 13 of 35 wells tested showed the presence of pathogens (37 percent).

In Summer 2019, 14 of 34 wells showed fecal contamination or pathogens from a human source (41 percent); four of 34 from a cattle source (12 percent); and one from a swine source (0.3 percent). In addition, 19 of 34 wells tested showed the presence of pathogens (56 percent).

The three County Conservation Departments are thankful for the continued participation of the area residents in the study.  “Without their permission to access their wells, we wouldn’t be able to continue collecting valuable data for the SWIGG Study,” said Grant County Conservation, Sanitation, and Zoning Administrator Lynda Schweikert.

Scientist’s analysis

The SWIGG scientists analyzed the samples for specific viruses and bacteria that indicate fecal contamination from human wastewater or livestock manure. Not all of these viruses and bacteria are capable of causing illness.

They found evidence of both human and livestock sources for the contamination, including manure from cattle and swine. In 16 of the 34 sampled wells the scientists found pathogens associated with gastrointestinal illness in humans. However, researchers have not calculated the health risk for these results, which vary based on the specific pathogen, its concentration, and the health of the person that drinks the water.

The SWIGG study has been designed to sample water in all four seasons of the year since contaminant abundance can vary seasonally. The percentage of wells that test positive is also expected to differ as weather and land use change over time.

They also emphasize that the percentage of contaminated wells from this sampling event do not 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 they will release the results when they are available. 

Phase three

The study team will also look for correlations between water quality, geology, and well construction. The study’s final report should be complete in early 2021. Iowa County Conservationist Katie Abbott described how the third and final phase of the study would be approached by the researchers.

“The researchers are compiling data for the various risk factors (e.g., land use, well construction, groundwater depth), and the statistical modeling requires the well water data, so it will begin when the sample analyses are complete,” Abbott explained. “The final report will likely be ready in early 2021.” 

Abbott said the team had originally planned to complete the study in late 2020, but the COVID-19 pandemic, according to her, has caused some delays.