GROUNDWATER MONITORING IN THE YELLOWSTONE CONTROLLED GROUNDWATER AREA, MONTANA

The 1994 compact between the State of Montana and the National Park Service created the Yellowstone Controlled Groundwater Area (YCGWA) to protect geothermal resources in Yellowstone National Park. In accordance with the compact the Montana Bureau of Mines and Geology developed a Long-Term Monitoring Program using a network of wells and springs to establish baseline water quality and water temperature conditions.

Monitoring began in 2005, and is focused around developed areas, including Cooke City along Soda Butte Creek, Gardiner along the Yellowstone River, Big Sky along the Gallatin River and West Yellowstone along the Madison River. The monitoring network consists of 28 sites, including 17 wells and 11 springs. The sites include 4 hot water sites (>25° C), 10 warm water sites (15° to 25° C) and 14 cold water sites (<15° C). Groundwater levels, spring discharge, temperature and water quality are measured.

Data show annual fluctuations in groundwater levels, spring discharge and water temperature. Water quality varies significantly among the sites. Geology and water temperature are important controls on water quality. Cold water sites tend to have calcium-bicarbonate or magnesium-bicarbonate type waters with low concentrations of major ions and trace metals; TDS concentrations range from 70 to 300 mg/l. Hot water sites tend to have sodium-calcium-sulfate type waters with higher concentrations of major ions and trace metals; TDS concentrations range from 1,300 to 2,400 mg/l. Warm water sites show the most variability in water quality. All data are available through the Groundwater Information Center at http://mbmggwic.mtech.edu.