Regional Groundwater and Aquifers

Groundwater is the water that fills the cracks and pores of rocks and sediments that lie beneath the surface of the earth — much the way water saturates a sponge. In the Twin Cities metro area, groundwater is an abundant but finite and vulnerable resource.

Groundwater is the source of drinking water for 75% of the people in the metro area. Groundwater is stored in the pore spaces of rock formations, called aquifers. The amount of water and how quickly it moves underground depends on the rock formation and pore space size.

The groundwater used in the metro area is pumped from one of four aquifers under the surface of the region: the Quaternary aquifer, the Prairie Du Chien-Jordan aquifer, the Tunnel City-Wonewoc aquifer, or the Mt. Simon-Hinckley aquifer.

The aquifers of the Twin Cities Metropolitan Area

Quaternary Aquifer

Extent: Variable across the metro
Geologic material: Discontinuous
and complex bodies of silt, sand,
and gravel
Yield: Moderate to high. Reported pumping capacity of metropolitan area municipal wells: 100 to 3,800 gallons per minute (average of 1,185)

Management concerns:

Challenging to identify the location of the most productive sand and gravel layers
First aquifer to be recharged
Vulnerable to contamination
Water quantity and quality varies

Prairie Du Chien-Jordan Aquifer

Extent: Not present across entire metro
Geologic material: Carbonate rocks and sandstone
Yield: High. Reported pumping capacity of metropolitan area municipal wells: 120 to 4,100 gallons per minute (average of 1,270)

Management concerns:

Not available to some growing communities
As the most heavily used aquifer in parts of the region, greater likelihood of water use conflict
Connected to some protected surface waters
Vulnerable to contamination, particularly where fractures exist and where bedrock above it has been eroded

Tunnel City-Wonewoc Aquifer

(formerly known as the Franconia-

Ironton- Galesville Aquifer)

Extent: Not present across entire metro
Geologic material: Sandstone and carbonate
Yield: Moderate to low. Reported pumping capacity of metropolitan area municipal wells: 115 to 1,600 gallons per minute (average of 700)

Management concerns:

Productivity varies greatly across the region and is highest where it is fractured or weathered
Connected to some protected surface waters
Vulnerable to contamination where fractured and where bedrock above it has been eroded

MT. Simon-Hinckley Aquifer

Extent: Throughout metro

Geologic material: Sandstone
Yield: High to moderate. Reported pumping capacity of metropolitan area municipal wells: 230 to 2,300 gallons per minute (average of 930)

Management concerns:

Use restricted by Minnesota law
Very slow recharge rate
Significant groundwater mining has occurred historically, creating a regional cone of depression
Relatively low vulnerability to contamination

For more information about groundwater, see the Groundwater Digest (PDF).