Groundwater study finds nitrate hotspots in Barron County’s sandy outwash areas; 11% of tested wells exceeded 10 ppm

Tyler Gritzmacher, Barron County conservationist, presented results from a multi-year groundwater monitoring study coordinated with the University of Wisconsin–Stevens Point Groundwater Center.

The study sampled private wells in 2022–23 with follow-up fill-in testing. Gritzmacher said the study identified a clear pattern: higher nitrate concentrations where agricultural land sits on well-drained, sandy outwash soils. He reported that about 11% of sampled wells exceeded 10 parts per million (ppm) nitrate, a common threshold for public-health concern. “We had a 30,” Gritzmacher said when asked about the highest nitrate value observed; he added that some publicly reported samples in the database registered in the 40s and 60s in isolated locations.

Why this matters: Nitrate in drinking water is primarily a human-health concern for infants and pregnant women at higher concentrations. The county presentation included maps showing predicted higher-nitrate areas east of Cameron, small pockets east of Rice Lake and east of Chetek, and concentration along the sandy corridor running roughly Rice Lake to Chippewa Falls.

Details and guidance: Gritzmacher said the distribution of high values correlates with two factors: an increased percentage of agricultural land cover within 500 meters of a well and sandier, better-drained soils that allow rapid recharge. He reported that 36% of wells tested were below 1 mg/L (natural background) and that public dashboards and individual results were available through the county Soil and Water Conservation Department. The presenter said the county did not test for PFAS as part of this study and noted that PFAS testing uses parts-per-trillion methods and targeted sampling.

Questions and county response: Supervisors asked whether contaminants correlated with abandoned manure pits, highway salt use, or septic systems. Gritzmacher said he saw no clear link to abandoned pits and noted salt and sodium are a separate concern tied to road density; he recommended household water testing and water-treatment systems for affected homeowners, explaining that drilling a new well is not guaranteed to find better water.

Outcome and next steps: The presentation provided a county baseline. Gritzmacher said homeowners who participated received individual test reports and that the county may pursue targeted follow-up testing for nitrates or pesticide metabolites in identified high-nitrate areas. No formal board action was taken on the study at the meeting.