Tracking Montana’s Groundwater

In Montana, more than 200,000 wells withdraw about 285 million gallons of groundwater per day. Most wells (93%) provide domestic or stock water, but account for only 12 percent of groundwater withdrawals; irrigation, public water supply, and industrial wells—7 percent of all wells—account for 88 percent of withdrawals.

Since 1993, the Montana Ground Water Assessment Program has been monitoring groundwater levels in the state’s major aquifers. The monitoring network consists of more than 900 wells, from less than 10 to more than 3,600 feet deep, that provide data for unconfined alluvial, deep basin-fill, and deep confined bedrock aquifers. Some of these wells have been consistently monitored since the 1950s.

Groundwater levels vary seasonally and from year to year in response to changing climatic conditions, nearby groundwater withdrawals, and changing land use. Data from the long-term monitoring network have helped document the effects of: (1) climatic variability on the Madison Limestone aquifer near Great Falls, (2) groundwater development on the Fox Hills–Hell Creek aquifer in eastern Montana, (3) land use impacts on the alluvial aquifers in southwest Montana, and (4) the dynamic adjustment of water-level fluctuations in response to groundwater development in the deep aquifer of the Kalispell valley in northwest Montana.

These examples highlight the importance of long-term, systematic groundwater-level monitoring to: (1) develop a comprehensive understanding of how aquifers respond to different stresses, and (2) develop meaningful evaluations of the groundwater supply.