Occurrence of Nitrate and Indicators of Agricultural and Septic System Contamination in a West Central Wisconsin Sand Aquifer


Fertilizers, manure, and septic effluent are potential sources of nitrate in groundwater. Nitrate can be harmful if ingested above the U.S. Environmental Protection Agency maximum contaminant level of 10 mg/L. In Eau Claire County, located in West Central Wisconsin, approximately one quarter of households rely on private wells. Sources of nitrate in private wells in Eau Claire County have not been researched previously.

A total of 110 private wells in Eau Claire County were tested for seven agricultural and three septic indicators to identify sources of nitrate contamination. Nitrate contamination risk factor data (e.g., well depth, casing depth) were also collected. Average nitrate concentrations were significantly higher in wells with agricultural indicators, suggesting agriculture is a source of nitrate. Wastewater indicators were identified, but septic systems were not a significant source of nitrate. Well casing depth was the only risk factor associated with elevated nitrate. Funds should be allocated to the Eau Claire City–County Health Department to promote and subsidize point-of-use drinking water treatment in homes with nitrate levels ≥10 mg/L. Further, new well casing depths should be >12 m (40 ft) to avoid infiltration of nitrate and other contaminants.


Speaker / Author: 
Laura Suppes, MPH, PhD, REHS, University of Wisconsin–Eau Claire
Ted Johnson, Eau Claire City–County Health Department (Retired)
Shane Sanderson, MS, JD, REHS, Linn County Department of Health Services
Sarah Vitale, PhD, University of Wisconsin–Eau Claire
Audrey Boerner, MS, Eau Claire City–County Health Department
Month Year: 
July 2022
Page #: 
Publication Month: 
July/August 2022
EH Topics: