Karst Aquifers: Madison Aquifer

The Madison aquifer underlies eight states in the U.S. and Canada: Montana, North Dakota, Wyoming, South Dakota, Nebraska, Alberta, Saskatchewan, and Manitoba. It is an important water resource in the northern plains states where surface water supplies are limited and population is increasing. Several of the larger communities and national parks in western South Dakota and Wyoming rely on water from the Madison aquifer. These include Rapid City, Spearfish, Hot Springs, and Wind Cave National Park in South Dakota and Gillette, Douglas, Sheridan, Buffalo, Devils Tower National Park, and the Wind River Indian Reservation in Wyoming. A growing population in western Montana may soon result in development of the Madison aquifer as a water supply. Declining water levels are a major issue for many of these communities. The response of Madison aquifer storage to changes in recharge rates is a critical issue because decreases in storage related to current drought conditions will continue if long-term climate change results in extended drought.

The Madison aquifer is part of a major aquifer system located in the northern Great Plains. During the U.S. Geological Survey investigations in this area, five major subdivisions of the aquifer system were recognized - the Cambrian-Ordovician, Madison, Pennsylvanian, Lower Cretaceous, and Upper Cretaceous aquifers. Each of these is an aggregate of permeable horizons and low-permeability, semiconfining material; each has been identified as an aquifer, primarily because vertical hydraulic-head differences within the unit tend to be smaller than those between it and the adjacent unit. To some extent, the division is arbitrary and was made to assist in analysis and discussion. Together, these five major aquifers comprise one of the largest confined aquifer systems in the United States.

Featured Studies and Datasets

Aquifer-scale studies and the datasets they produce are a key component to understanding how karst aquifers behave, and the quality of water within them.

• Source-water determination using water chemistry, near Wind Cave Nat. Park — A study to better understand groundwater flow through the Madison aquifer using end-member mixing models.
• Madison Aquifer Study in the Rapid City Area — A long-term group of hydrologic investigations to better understand the complex system that supplies water to Rapid City and the surrounding area.

Additional Information

The following websites are additional sources of information about this aquifer:

• Madison Aquifer Study in the Rapid City Area
• The Madison Room: A virtual field trip (by Rod Benson)
• Lewis & Clark Caverns State Park, Montana
• Giant Springs State Park, Montana
• Black Hills Hydrology Study