Groundwater is stored in aquifers, which are layers of sand, gravel or bedrock filled with water. The bedrock geology of Dakota County consists of alternating layers of limestone, dolomite, sandstone and shale. In general, the deeper the aquifer, the older the groundwater and less 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, households and farms. The most common human-caused contaminants in the county are nitrate from agriculture and septic systems and chloride from de-icing salt, water softeners and fertilizers.
There are also geologically sourced contaminants in the rocks and soil underground that dissolve into the groundwater. These include arsenic and manganese.
To learn more about Dakota County aquifers and common groundwater contaminants, see the Groundwater Quality Story Map.