Quantitative microbial risk assessment for contaminated private wells in the fractured dolomite aquifer of Kewaunee County, Wisconsin

Authors: Burch, Tucker; STOKDYK, JOEL - Us Geological Survey (USGS); Spencer, Susan; KIEKE, BURNEY - Marshfield Clinic Research; FIRNSTAHL, AARON - Us Geological Survey (USGS); MULDOON, MAUREEN - Wisconsin Geological And Natural History Survey; Borchardt, Mark

Submitted to: Environmental Health Perspectives
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2021
Publication Date: 6/23/2021
Citation: Burch, T.R., Stokdyk, J.P., Spencer, S.K., Kieke, B.A., Firnstahl, A.D., Muldoon, M.A., Borchardt, M.A. 2021. Quantitative microbial risk assessment for contaminated private wells in the fractured dolomite aquifer of Kewaunee County, Wisconsin. Environmental Health Perspectives. https://doi.org/10.1289/EHP7815.
DOI: https://doi.org/10.1289/EHP7815

Interpretive Summary: As in many other areas of the nation, private wells in Kewaunee County are an important source of drinking water, and they are vulnerable to contamination by fecal waste from livestock (associated with intensifying livestock production in the region) and humans (associated with exurban housing developments). This fecal waste carries pathogenic microorganisms that can cause acute gastrointestinal illness (AGI) when consumed in water, but the extent of AGI cases caused by drinking water from contaminated private wells in Kewaunee County is currently unknown. This study used quantitative microbial risk assessment (QMRA) and a county-wide pathogen occurrence study to predict the number of AGI cases per year in the county due to contaminated private wells. The results suggest that several hundred AGI cases per year are caused by consuming contaminated private well water in Kewaunee County, and that more than half of these cases are potentially associated with bovine fecal material in contaminated wells. Furthermore, results are useful for prioritizing potential policy interventions in Kewaunee County and are also informative with regard to the impact of livestock agriculture on water resources in other similar areas of the nation.

Technical Abstract: Private wells are an important source of drinking water in Kewaunee County, Wisconsin. Due to the region’s fractured dolomite aquifer, these wells are vulnerable to contamination by human and zoonotic gastrointestinal pathogens originating from land-applied cattle manure and private septic systems. However, the magnitude of the health burden associated with this contamination is unknown. This study combined quantitative microbial risk assessment (QMRA) with a year-long county-wide pathogen occurrence study in order to predict total cases of acute gastrointestinal illness (AGI) caused by private well contamination in the county. It also used microbial source tracking to associate predicted cases with bovine, human, or unknown fecal sources. Results suggest that private well contamination could be responsible for as many as 301 AGI cases yr-1 in Kewaunee County, and that 230 cases yr-1 were associated with a bovine fecal source (human: 12 cases yr-1, unknown: 59 cases yr-1). Furthermore, Cryptosporidium parvum was predicted to cause 190 cases yr-1, the most out of all 8 pathogens included in the QMRA. These results have important implications for land use and water resource management in Kewaunee County and inform the public health impacts of consuming drinking water produced in other similarly vulnerable hydrogeological settings.