|STOKDYK, JOEL - Us Geological Survey (USGS)|
|FIRNSTAHL, AARON - Us Geological Survey (USGS)|
|BRADBURY, KENNETH - Wisconsin Geological And Natural History Survey|
|MULDOON, MAUREEN - Wisconsin Geological And Natural History Survey|
|KIEKE, BURNEY - Marshfield Clinic Research|
Submitted to: Government Publication/Report
Publication Type: Government Publication
Publication Acceptance Date: 5/13/2022
Publication Date: 5/16/2022
Citation: Stokdyk, J., Borchardt, M.A., Firnstahl, A., Bradbury, K., Muldoon, M., Kieke, B. 2022. Assessing private well contamination in Grant, Iowa, and Lafayette counties, Wisconsin: The southwest Wisconsin groundwater and geology study. Government Publication/Report. 2022.
Technical Abstract: Rural residents of Grant, Iowa, and Lafayette Counties in Wisconsin rely on private wells for their water. Contaminants like nitrate and bacteria from septic systems, fertilizer, and manure can contaminate the groundwater that residents use. Groundwater is vulnerable to contamination where the soil layer is thin and the bedrock is fractured, which is the case for much of the study region. This study was designed to assess and understand private well water contamination in the three counties. Overall, 126 (42%) of 301 wells sampled in November 2018 and 145 (27%) of 539 wells sampled in April 2019 were positive for total coliform bacteria and/or had nitrate greater than the Wisconsin and USEPA health standard (10 mg nitrate-nitrogen per liter). Among wells positive for coliform bacteria or with high nitrate, 138 were randomly selected for additional testing. Human wastewater was detected in 64 wells, cattle manure was detected in 33 wells, and pig manure was detected in 13 wells, indicating that both human wastewater and livestock manure contribute to private well contamination. Pathogens were detected in 66 of the 138 wells (48%). Nitrate contamination was generally greater where the geology allows rapid flow of water and contaminants. Microbial contamination was generally greater following periods of rainfall and where bedrock is closer to the surface. Both nitrate and microbial contamination were generally greater for older, shallower wells. Human wastewater contamination was greater for wells closer to septic systems and for wells with more septic systems nearby. Septic systems were not associated with nitrate and total coliforms. Nitrate and total coliform contamination were greater for wells closer to farms or cultivated land for crops. Also, nitrate contamination increased when there was more cultivated land nearby. By identifying multiple sources and factors related to private well contamination, the study may be used when considering potential priorities for groundwater quality. Importantly, the study goes beyond a description of contamination, and it may also be used to inform efforts or actions that address contamination. Together, these two outcomes provide a unique contribution to groundwater science and a detailed characterization of private well drinking water quality for the residents of southwest Wisconsin.