GROUNDWATER LEVELS, SPRING DISCHARGE, WATER QUALITY MONITORING, AND WELL PERMITTING IN THE YELLOWSTONE CONTROLLED GROUNDWATER AREA, MONTANA

In 1994 the State of Montana and the National Park Service (NPS) signed a Water-Rights Compact that established reserved water rights for NPS lands in Montana, adjacent to Yellowstone National Park (Park). The Compact included establishment of the Yellowstone Controlled Groundwater Area (YCGA), encompassing 1,170 mi² of land in Montana adjacent to the Park. The Montana Department of Natural Resources and Conservation (DNRC) administers the YCGA and requires a permit for any wells drilled since 1994, with the permitting requirements including reporting the groundwater temperature. The Compact also required establishment of a groundwater monitoring program, which is administered by the Montana Bureau of Mines and Geology (MBMG). The NPS provides funding support to DNRC and MBMG to support the Compact requirements.

In 2005 MBMG established the groundwater monitoring program, with monitoring focused around developed areas in the YCGA, including Cooke City, Silver Gate, Gardiner, and West Yellowstone, Montana. Currently the monitoring network consists of 36 sites that are a mix of hot- (>25° C), warm- (15° to 25° C) and cold-water wells and springs. The data collected includes groundwater levels, spring discharge, water temperature, and inorganic water chemistry.

The MBMG has compiled data on groundwater levels, spring discharge, water temperature and water quality, and defined baseline conditions within the YCGA. Water quality varies significantly among the sites, depending on the geology and groundwater temperature. Cold water sites tend to produce calcium-bicarbonate or magnesium-bicarbonate type waters with low concentrations of major ions and trace elements, while hot water sites tend to have sodium-calcium-sulfate type waters with high concentrations of major ions and trace elements. Total dissolved solids (TDS) concentrations at the cold-water sites generally range from 70 to 300 mg/L, while hot-water sites have concentrations that range from 1,300 to 2,400 mg/L. All of the groundwater level, spring discharge, water temperature, and inorganic water chemistry data are available through the Groundwater Information Center at http://mbmggwic.mtech.edu.