We are blessed with an abundance of ground water in this part of the state. In fact, it is estimated that 70% of Minnesotans use ground water as their source of drinking water. Wise stewardship of this resource is of the utmost importance.
Just like surface water, ground water is affected by point source and non-point source pollution. Point source contamination is traceable to 1 specific site or spill. Non-point source pollutants, such as pesticides and herbicides are also very common and can collectively have a broad impact on our groundwater resources. Poorly functioning septic systems can also contribute excess nitrogen and phosphorus to the soil and groundwater. Contamination due to surface or bedrock geology is also possible.
Crow Wing County recently completed the geologic atlas of the county. It contains a number of detailed maps and charts showing not only the surface and bedrock geology of the area, but also the location and depth of aquifers and the sensitivity of these aquifers to contamination. It also maps the abundance of minerals in Crow Wing County.
The public health and economic development of Crow Wing County are directly dependent on the wise use and management of its land and water resources. Geologic and hydrologic information are essential before decisions are made that affect natural resources.
County atlases, prepared jointly by the Minnesota Geological Survey and the Minnesota Department of Natural Resources, Division of Waters, present detailed geologic and hydrologic information in an interpretive as well as descriptive form. Maps and texts either summarize basic geologic and hydrologic conditions at a county scale, or interpret these conditions in terms of the impacts of possible land and water use decisions.
Crow Wing County's surficial geology (materials expected to be encountered at the land surface beneath the topsoil) is comprised of 3 types of material: till (unsorted sediment deposited by glacial ice), sand and gravel, and lacustrine (old lake bed) sand.
Most groundwater supplies in Crow Wing County are pumped from the surficial sand aquifer and several buried sand aquifers. The surficial sand aquifer has very little protective cover and the water table is generally shallow, so sensitivity to pollution of the surficial aquifer is very high to high. The sensitivity of the buried aquifers depends upon the thickness of till that overlies the aquifer. Chemistry and tritium data indicate that the surficial aquifer and shallow buried sand aquifers that lie below the surficial aquifer are readily recharged. Recharge is slower for buried sand aquifers that lie below till units.
The interaction of lakes and groundwater plays an important role in the variability of lake water elevation over time, and in areas where ground water is flowing into a lake, poor ground-water quality can lead to poor lake-water quality.
The Geologic Atlas of Crow Wing County, Minnesota is comprised of 10 plates, each with maps and text descriptions of a specific component of the Atlas. Several of the most important plates with respect to water quality are highlighted below:
- Plate 1, Data Base Map
- Plate 2, Bedrock Geology
- Plate 3, Surficial Geology
- Plate 4, Quaternary Stratigraphy
- Plate 5, Bedrock Geology
- Plate 6, Mineral Endowment
- Plate 7, Hydrology of the Buried and Surficial Aquifers
- Plate 8, Hydrogeoloci Cross Sections
- Plate 9, Pollution Sensitivity of the Buried and Surficial Aquifers
- Plate 10, Interaction of Lakes and Ground Water