Minnesota Profile: Groundwater

Appearance

The water Minnesotans draw from wells is groundwater-freshwater from underground. Groundwater and surface water are connected. Groundwater feeds streams, lakes, and wetlands. Surface waters, in turn, help recharge groundwater. Natural pressure can force groundwater to the surface, creating seeps and springs. Springs feed streams and lakes.

Source

About 97 percent of Earth's liquid freshwater is below ground. Groundwater begins as precipitation. Rain or snowmelt spills into cracks in the earth, soaks into pores between soil or rock particles, and slides into sinkholes. In southeastern Minnesota, groundwater travels like a river through underground caves and channels in limestone bedrock. But groundwater usually moves through soil at a rate of only a few inches per year. Over millennia, water has saturated all of the spaces in geological formations known as aquifers (Latin for that which carries water). The top of the saturated zone in the aquifer is the water table.

Range

Most areas of Minnesota have deposits of water-bearing rock or sand and gravel. The map (right) shows the availability of groundwater.

Human use

About 75 percent of Minnesotans tap into aquifers for drinking water. We pump more than 120 billion gallons per year for homes, industries, and businesses. Public water supplies and irrigation use the most.

Management issues

Adequate groundwater levels sustain stream flow and lake levels, especially during drought. Pumping diverts groundwater, changing surface-water levels, flow, and even temperature. For instance, pumping for irrigation wells draws cold groundwater away from the Straight River and thus boosts stream temperature.

To sustain underground levels, as well as surface-water levels, the volume and rate of water withdrawal must be less than recharge. Pavement, buildings, and other impermeable surfaces reduce the amount of water that percolates down to recharge aquifers.

The Pollution Control Agency monitors water quality. Contaminants from highways, lawns, landfills, industries, and agriculture can reach aquifers. But because infiltration occurs slowly, contamination can go unnoticed for decades.

The DNR maps aquifers and issues water-use permits to balance competing demands and to protect natural resources.

You can help protect groundwater by conserving it, properly disposing of hazardous waste, and reducing use of fertilizers and other chemicals.

Kathleen Weflen