Gallatin County Groundwater Nitrate and Water Levels

Gallatin County, Montana has been experiencing rapid residential development with extensive reliance on onsite (septic) wastewater systems. Groundwater in the alluvial valley of the county surrounding the Gallatin River and tributaries is relatively shallow and vulnerable to increasing concentrations of nitrate and potentially other contaminants from anthropogenic sources. This data resource includes groundwater nitrate concentrations from three different sources combined and made publicly available for the first time. The resource includes tabulated nitrate concentration point data as well as a geospatial component including the mapped concentrations and spatially interpolated nitrate concentrations. The resource also includes static water levels measured at the time of new well drilling and spatially interpolated depth to groundwater based on those data. Groundwater nitrate data continues to become available through new testing and curation of past records, so parallel future data resources will include more information.
The purpose of the spatially interpolated nitrate concentration map is to identify locations where nitrate concentrations are elevated over a relatively continuous area, where multiple proximal sample locations show concentrations above 3 mg/L. Nitrate concentrations can be highly variable across space and depth within aquifers. The identified areas are not the only places in the Gallatin Valley where nitrate concentrations are above 3 mg/L, nor are all groundwaters within the designated areas above 3 mg/L. These results are a simplified summary of nitrate data compiled as of July 25th, 2024 and this analysis will continue to be refined over time.