Correlating bedrock folds and fractures to arsenic detection in drinking water, southeast Wisconsin

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  • Eric Stewart, UW-Madison
  • Esther Stewart, UW-Madison

Arsenic release mechanisms into groundwater wells and bedrock sources of arsenic have been well studied in Outagamie and Winnebago counties in northeastern Wisconsin. A thorough understanding of arsenic release and arsenic source led to special well construction guidelines that have helped mitigate well water contamination in those counties. However, the structural setting for Paleozoic bedrock aquifers changes to the south, and this may impact the distribution of bedrock arsenic sources and the probability of detecting arsenic in groundwater wells. In Fond du Lac, Dodge, and Jefferson counties, broad, low-amplitude folds and fracture networks become more common compared to the betterstudied Outagamie and Winnebago counties to the north. Preliminary analysis of publicly available WDNR groundwater samples from wells drawing from the St. Peter aquifer near the newly mapped Beaver Dam Anticline, Dodge County, suggests the probability of detecting arsenic in well water close to the fold axis is statistically higher than away from the fold axis. This project proposes to test for potential structural and stratigraphic reasons for the increased risk near the Beaver Dam Anticline, and map and test additional folds for a similar relationship. Specifically, this project will expand the structural mapping and bedrock arsenic source characterization by identifying new folds in Paleozoic bedrock, determining macro, meso, and micro scale changes in bedrock arsenic sources, and use existing water quality data to determine if changes in bedrock arsenic sources leads to changes in the probability of detecting arsenic.

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