Citizen Groundwater Monitoring Program


St. Croix County’s population is nearing 90,000 people and groundwater is the sole source of residential drinking water supply. Approximately 50% of the population in St. Croix County relies on private wells for drinking water, and private well owners are responsible for drinking water testing and treatment. The Citizen Groundwater Monitoring Program (CGMP) is a 5-year groundwater study that began in the fall of 2019. The program aims to understand long-term trends in groundwater nitrate contamination throughout the County through annual sampling of the same wells for the program duration, and provides participants with five years of free water testing. The program also aims to gain a better understanding of St. Croix County groundwater aquifer health and determine the primary factors that contribute to a private drinking water well’s susceptibility to contamination in St. Croix County. The program samples private wells on a voluntary basis across the county and would not be possible without citizen participation.

Research has identified nitrate as one of the primary groundwater contaminants of concern in the Midwest. Groundwater nitrate occurs naturally at low levels (generally less than 1 mg/L), however concentrations greater than 1 or 2 mg/L indicate input from human activity. A variety of human activities can result in groundwater nitrate contamination, including the application of commercial fertilizer or manure to cropland, certain types of industrial activity, and domestic practices such as use of lawn fertilizer, improper disposal of pet waste, and septic systems.

Preliminary Results

Analysis of the first year data included 178 private well water samples, of which 23 samples (13%) exceeded the 10 mg/L drinking water standard for nitrate. Statistical analysis also indicates that a private well’s susceptibility to nitrate contamination is predominantly correlated to the well’s casing depth and the surrounding land use. To learn more about the CGMP, please visit the Citizen Groundwater Monitoring Program Web Experience for details regarding the project background, groundwater basics, and an expanded discussion of the first year preliminary data analysis. As the program continues, yearly data analysis will be completed and will include trend analysis as sufficient data becomes available.

Citizen Groundwater Monitoring Program (CGMP) Year 5 Report

Additional Information

To learn more about the purpose of this program, please view the Prioritized Recommendations from the Ground & Surface Water Quality Study report.