Fort Peck Dam creates the country’s sixth-largest reservoir. This and at least 800 other dams hold back billions of gallons of surface water for farmers, ranchers, and city folks.

Montana’s underground aquifers store billions of gallons more. Groundwater wells punched into that aquifer has fueled much of the state’s residential growth. As a consequence, studies show groundwater levels in a few areas may be falling.

Declining well levels since 1980. (Dataset includes MBMG data in NYTimes.com graphic)

The Water Policy Interim Committee of the Montana Legislature is studying ways to increase water storage. Much of the committee’s discussion has revolved around repairing existing surface water infrastructure and expanding the use of underground storage and natural storage.

Montanans are already adding to underground water storage–although perhaps inadvertently. The Montana Bureau of Mines and Geology presented evidence to the WPIC that leaky irrigation ditches and canals are, in fact, doing more than delivering water to users. These ditches and canals are recharging in the aquifer.

MBMG experts say this “agricultural managed aquifer storage” (Ag MAR) may be the most immediate and cheapest way to increase below-ground water storage. But adverse impacts from Ag MAR projects may include sediment loading in rivers, soil leaching, low oxygen conditions, and lower soil fertility. To find out where Ag MAR projects might be most beneficial, MBMG scientists are developing a state-wide suitability map for release perhaps this year on the bureau’s web portal.