2.5.6 Groundwater

There are a number of springs and seeps in the Mississippi River gorge area, including Camp Coldwater Spring, the largest limestone bedrock spring in the Metro area.    Hydrologic analysis and monitoring completed by the District in 2000/2001 indicating potential construction impacts to the springflow led to a requirement that the Minnesota Department of Transportation modify its design for a new interchange at TH 55 and TH 62.  The District is continuing to monitor the spring to evaluate long-term trends.

Minnehaha Creek flow monitoring indicates that some reaches of the creek may be gaining baseflow from groundwater while other reaches may be losing baseflow, likely from a combination of natural geologic conditions and the artificial creek elevation modifications at the weirs and dams.  The District is expanding its monitoring program to better understand the extent of these areas of infiltration (gain) and exfiltration (loss).

The HHPLS identified the infiltration potential of the upland areas within the subwatershed as high to medium with some areas of variability where the soils are organic in nature (see Figure 16).   Most of the lower subwatershed is classified by the Hennepin County Geologic Atlas as being of high to very high aquifer sensitivity, reflecting the glacial outwash deposits that underlay the soils and the shallow depth to bedrock.  The upper subwatershed, an area of loamy till, is classified as being generally of low to moderate sensitivity to pollution except along the Creek and in the large Grays Bay wetland complex (see Figure 17). 

Large areas of the upper subwatershed have been designated by the Minnesota Department of Health (MDH) as Wellhead Protection Areas, including three in St. Louis Park, four in Minnetonka, and eight in Edina.   The Drinking Water Sensitivity Management Areas (DWSMA) for St. Louis Park wells have been designated by the MDH to be of high risk and vulnerability to contamination of the drinking water supply while the DWSMAs for the other wellhead Protection areas are generally of low vulnerability.  Figure 18 shows the DWSMAs and associated Wellhead Protection Areas.

The County Well Index has records of approximately 975 wells in the subwatershed, mostly shallow (less than 300 feet deep) domestic water supply wells but about 30 wells deeper than 500 feet, mostly municipal supply wells.