Results of 2020 Green Lake County Drinking Water Study

In the fall of 2019, the Green Lake County Health Department (GLHD) secured an Environmental Health Tracking Grant from the Wisconsin Department of Health Services to “protect and enhance the groundwater in Green Lake County.” Sampling was completed in early March of 2020. Several parameters were tested for including bacteria, nitrate, and pH. Due to the overwhelming requests for participation in the project, the GLSD funded the 111 samples taken within the Green Lake watershed. By doing so, the GLSD would not only help ensure the health of residents within the District, we would also gain critical information regarding possible
high nitrate levels impacting the lake.

Nitrate is a nutrient commonly found in agricultural and lawn fertilizer as well as septic system effluent. The drinking water standard for nitrate-nitrogen is 10 mg/L. Water with greater than 10 mg/L of nitrate-nitrogen should not be consumed by infants less than 6 months of age, pregnant women, and women who are trying to become pregnant. Some studies suggest that high nitrate water may be linked to birth defects, miscarriages, and several types of cancer. The WI Dept. of Public Health recommends people of all ages avoid long-term consumption of water with nitrate concentrations greater than 10 mg/L.

In total, the study sampled 263 wells throughout the county. Specific to nitrate, 48 out of the 263 samples (18%) showed levels of nitrate above the health standard of 10 mg/L. Within the watershed, 17 out of 111 samples (15%) showed levels above 10 mg/L. These sites correlated strongly to areas of intensive agriculture with additional factors of sandy soils or shallow bedrock possibly being a contributing factor. Approximately 20 samples taken within the watershed were adjacent to Green Lake itself. Of these shoreland samples, only one (taken in the Terrace area) showed nitrate levels over the health standard. While this property is located very close to agricultural lands that could be impacting local groundwater nitrate levels, samples taken from other properties in the terrace did not show high nitrate levels. Overall, the study results indicate that nitrate is entering the lake through groundwater, but at levels below the current health standard. The GLSD and the lake management team are working hard to reduce nutrient levels entering the lake from agricultural runoff, aging septic systems, construction site erosion, and other known sources.