GRANT, IOWA AND LAFAYETTE COUNTIES - The Southwest Wisconsin Groundwater and Geology Study (SWIGG) for Grant, Iowa, and Lafayette counties completed its fourth and final round of private well sampling to identify fecal sources of contamination in drinking water. This concludes the second phase of the three-part study of well water quality in Grant, Iowa and Lafayette counties.
Three phases of studyPhase One:sampling of 840 randomly selected wells in the three counties for coliform bacteria and nitrate (Nov. 2018 and Apr. 2019).
Phase Two:resampling of some wells found to be contaminated with coliform bacteria or nitrate in Phase One four times in the course of a 12-month period: spring, summer fall of 2019, and winter of 2020.Phase Three:The study team will also look for correlations between water quality, land use, geology, and well construction. The study’s final report should be complete in early 2021.
Phase Two complete
The final round of microbial source testing in the second phase of the SWIGG Study is now complete with the announcement last week of the Winter 2020microbial source testing results.
In March 2020, scientists randomly selected 35 private wells after earlier sampling found they were contaminated with coliform bacteria or nitrate levels above the drinking water standard. The latest phase of the study found fecal contamination in 17 of those 35 wells (49 percent).
In this round of sampling, eight of 35 wells showed fecal contamination or pathogens from a human source (23 percent); two of 35 wells from a cattle source (six percent); and four of 35 wells from a swine source (11 percent).
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 can cause illness. Scientists found evidence of human, cattle, and swine contamination sources.
In 17 of the 35 sampled wells (49 percent), the scientists found pathogens associated with gastrointestinal illness in humans. However, researchers have not calculated the health risk for these results, which depends on the specific pathogen, its concentration, and the health of the person who drinks the water.
Thanks and cautions
The three County Conservation Departments are grateful to area residents for their participation.
“We want to thank all the well owners that made this study possible,” said Katie Abbott, County Conservationist with the Iowa County Land Conservation Department. “We look forward to working with stakeholders further once the study is complete.”
The researchers emphasize it is too soon to draw study conclusions. Although the well sampling is completed, comprehensive data analysis is still ongoing.
Researchers also emphasize that the percentage of contaminated wells from this final phase two round of sampling do not represent the entire region because they were chosen from wells already shown in phase one of the study to be contaminated.
Phase Two: first three source test samplings
Spring 2019: In this first of four seasonal samplings, 13 of 35 wells tested (37 percent) contained detected pathogens. Regarding the microbial source of the pathogens, 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).
Summer 2019:In this sampling, 19 of 34 wells tested showed the presence of pathogens (56 percent). Regarding sources of pathogens, 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).
Fall 2019:This sampling found fecal contamination or pathogens in 27 of the 34 private wells sampled (80 percent). According to the researchers, 12 of 34 wells 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).
First phase results
The study began in late 2018 to assess private well water quality in southwest Wisconsin and determine probable sources of any contamination found. The study’s goal is to test 500 wells randomly selected throughout the three counties. It is estimated that there are 2,199 private wells in Grant County; 5,829 in Iowa County; and 3,000 in Lafayette County. This means that a sample of 500 will represent five percent of the total approximately 11,000 private wells.
The first samples (301) were taken on Friday, Nov. 9, and the second round of samples (539) were taken in April of 2019.The first phase of testing in the SWIGG Study employed a much less expensive and technically difficult testing method. Well owners who participated received information about levels of coliform bacteria and nitrate in their wells.
The November 2018 results were released in January of 2019. Those results showed that 42 percent of the randomly selected wells exceeded federal health standards for coliform, E.coli or nitrates.
Overall, 27 percent of the 539 wells tested in April of 2019, did not meet health standards for total coliform, E. coli, or nitrate. This is less than the 42 percent that tested positive in November 2018.
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.
Approximately 44 percent of the population in the three counties relies on private groundwater wells for their drinking water. Together these residents are served by over 18,000 known wells with construction records, in addition to wells without records available.
Private wells are not monitored or regulated by federal, state or local government. Instead, homeowners are responsible for the maintenance and testing of their private well, including any treatment or corrective action to address contamination. Contamination of private wells is commonly assessed using tests for nitrate and indicator bacteria (total coliform and E. coli).
Existing data from the online CWSE well water quality viewer show that across the three counties, 13 percent of 4,283 samples exceeded the nitrate drinking water standard of 10 mg/L, and 29 percent and three percent respectively of 1,747 samples were positive for total coliform bacteria and E. coli.
Samples collected for these measurements are voluntary and therefore may not reflect the true extent of contamination as certain geographic areas or geologic settings may be over- or under-represented. And even when the tests show up positive, they still don’t identify the source of the pollution.
Private well contamination can be related to the vulnerability of specific wells or general groundwater contamination by sources on the landscape. Elevated nitrate in groundwater can result from both inorganic fertilizers and fecal sources, while indicator bacteria typically originate from fecal sources.
Given the mix of land uses in rural areas, fecal contamination can originate from agricultural operations through land application of manure, and from homes with septic systems that discharge wastewater through drainfields (e.g. mound systems). Therefore, both agricultural and residential fecal sources can contribute to nitrate and bacteria contamination of private wells, and hydrogeological factors influence the vulnerability of groundwater to these contaminants.
Grant, Iowa and Lafayette counties are in the Driftless Area of southwest Wisconsin. Unlike much of northern and eastern Wisconsin, these counties were not covered by glaciers, so the landscape is much older than the glacially-modified landscapes found in other parts of the state.
The uppermost bedrock in the region is mostly dolomite and limestone of the Ordovician-age Sinnipee and Prairie du Chien groups. These carbonate rocks contain fractures and karst features such as sinkholes, conduits, and small caves. Generally in the three counties, these rocks are within 50 feet of the surface, qualifying as shallow soil-to-bedrock areas.
Much of the uplands in the three counties are covered with a silty-clay material known as the Rountree Formation, named after exposures along Rountree Creek in the city of Platteville. This soil type is a mix of weathered carbonate bedrock and loess or windblown silt deposited during the Pleistocene age. Over the three counties, the thickness of this soil layer ranges from absent to several feet thick.
Groundwater can occur in any of the rock formations in the three counties, depending on the elevation of the water table. All of these sandstone layers form interconnected aquifers. Deep wells in this area receive most of their water from the Cambrian sandstone aquifer, but locally shallower wells are finished in the rocks of the Sinnipe or Prairie du Chien groups or in the St. Peter Sandstone. Along major river valleys sand-and-gravel aquifers supply water to wells.
Water well construction characteristics can govern the susceptibility of wells to contamination. Although not mandated by the current Wisconsin well code, it is recommended that water wells be cased (a steel casing pipe cemented into the well) to below the water table. Otherwise, an uncased hole provides a direct conduit for potentially contaminated water to move from near the land surface into the well and into deep aquifers.The study was initiated by Grant, Iowa, and Lafayette Counties in collaboration with researchers from the U.S. Department of Agriculture, the Wisconsin Geological and Natural History Survey-University of Wisconsin-Madison Division of Extension, 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.