Where are these nitrates coming from?

Previous studies of this aquifer and existing peer-reviewed studies on how nitrates get into groundwater clearly conclude the elevated nitrate concentrations in the aquifer below Seeley Lake could only be the result of pollution from septic systems. Hydrogeologic studies and USGS projections estimate that the natural concentration of nitrates in groundwater in this region would be between 0.6mg/L and 1.0 mg/L. This is significantly lower than the nitrate levels in the Seeley Lake Sewer District monitoring data. This contamination is not caused by natural processes. There are generally four human activities or conditions that could lead to nitrate contamination in groundwater: concentrated and/or confined animal feeding operations; large-scale, fertilized agriculture operations; nitrate/nutrient discharge from industrial operations; and discharge from septic systems. There are no animal feeding operations, no large-scale fertilized agriculture operations and no industrial discharge sources in the Seeley Lake area, but there are many septic systems.

In 2023, the Sewer District hired a third-party consultant to analyze samples from several wells to determine if the cause of the contamination was from human waste, or some other source. Those results were released in 2024, and every sampled well showed that the contamination was linked to human sewage.