Groundwater supplies 75 percent of Minnesota's drinking water. Here in Dakota County, groundwater supplies more than 90 percent of the drinking water.
Groundwater and the water cycle
Groundwater is a key part of the hydrologic (water) cycle. The water cycle is the continuous movement of water in the air, on the land, and below Earth's surface.
Precipitation
The cycle begins when water falls to the ground as rain and snow.
Runoff or infiltration
After precipitation lands on the ground, it does one of two things:
- Runs off the land into lakes, rivers and wetlands.
- Soaks into the soil, a process called infiltration
Plants and transpiration
Some water that infiltrates is taken up by plants. Plants release this water back to the air through a process called transpiration.
Recharging groundwater
The remaining water continues to move downward, slowing filling in the spaces between sediment and rocks underground. This is how groundwater is created and replenished or recharged. How fast water soaks into the ground depends on the type of soil, vegetation and other factors.
Movement of groundwater
Groundwater moves from higher elevation to lower elevation, flowing slowly through the ground until it reaches a place where it comes back to the surface – such as a lake, stream, wetland or ocean. In Dakota County, our groundwater either flows towards the Minnesota River or the Mississippi River.
Once groundwater becomes surface water, it can infiltrate downward again to recharge the groundwater. It can also evaporate into the air, forming water vapor, where it forms clouds and falls as precipitation again.
Wells
We use groundwater for drinking water by pumping it from underground using wells. A well works like a straw. Like a straw pulls liquid out from spaces between ice cubes in a cup a well pulls water from spaces between soil, sand and rocks.
A pump brings the groundwater up to the surface. There, it can be used in houses, on farms, or in city water systems for drinking, washing, irrigation and many other purposes.
Learn more about the basics of groundwater and find resources for classrooms, at these websites:
Groundwater quality
Groundwater is stored in aquifers, which are layers of sand, gravel or bedrock filled with water. In Dakota County, the bedrock is made up of layers of limestone, dolomite, sandstone and shale. Usually the deeper the aquifer, the older the groundwater and less likely to have human-caused contaminants.
Groundwater contamination in Dakota County is dependent upon land use and soil types. Most soil types in the county are sensitive to groundwater contamination, meaning that surface pollution can reach the groundwater within a few hours.
Contamination can come from several different sources, including industries, homes, and farms. The most common human-caused contaminants in the county are:
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Nitrate from agriculture and septic systems
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Chloride from road salt, water softeners and some fertilizers.
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Industrial contaminants from landfills, improper waste disposal, and former dry-cleaning sites. You can learn more about these sources and locations in the
Minnesota Groundwater Contamination Atlas.
Some contaminants occur naturally in the rocks and soil underground – called geogenic contaminants. As water moves through these materials, substances like arsenic and manganese can dissolve into the groundwater. To learn more about Dakota County aquifers and common groundwater contaminants, see the Groundwater Quality Story Map.
Current groundwater levels
Rainfall varies from year to year, impacting the surface water and groundwater levels in Dakota County. Too much rainfall over a short period of time can result in floods. Too little rainfall over an extended time can result in a drought.
Find out more about current water conditions in Dakota County:
Dakota County weather stations