Figure 1. Minnesota groundwater provinces.
Minnesota is generally considered to have abundant groundwater. But that resource is not evenly distributed across the state. That uneven distribution can limit the amount of groundwater available to industry and development in some areas. The Minnesota Groundwater Provinces map summarizes aquifer and groundwater resource differences at the regional level.
The occurrence of groundwater in Minnesota is related primarily to local geologic conditions that determine the type and properties of aquifers. Figure 1 shows the six groundwater provinces of the state based on bedrock and glacial geology. Within each province, groundwater sources and the availability of groundwater for drinking water, industrial, and agricultural uses are similar.
The aquifers within these provinces occur in two general geologic settings: bedrock comprising a wide range of rock types and ages, and unconsolidated sediments deposited by glaciers, streams, and lakes. The combination of physical aquifer attributes (thickness, lateral extent, permeability, and porosity type) of the two settings distinguishes the six groundwater provinces within the state.
Figure 2 shows two generalized geologic cross sections that illustrate subsurface conditions along lines A-A' and B-B' on Figure 1.
Figure 3. Bedrock aquifer types.
Bedrock type divides the state into two bedrock aquifer regions (Figure 3). In the southeastern third of Minnesota the bedrock aquifers consist of thick, laterally extensive sequences of sandstone, limestone, and dolostone of sedimentary origin. These layers are shown on the generalized cross sections (Figure 2) as the light blue stippled layers. In these bedrock aquifers, groundwater occurs in granular pore spaces, partings, joints, fractures, and dissolution features. Karst features are common in bedrock in the extreme southeast. Conditions vary locally, but generally these aquifers are capable of yielding sufficient quantities of groundwater for most purposes.
The remainder of the state, as well as the sedimentary bedrock in the southeast part of the state, is underlain by bedrock of hard, and very old, igneous and metamorphic rocks (dark blue layer on cross sections). Groundwater in these rocks occurs mostly in fractures that may not yield useable quantities of water. Above the hard, fractured bedrock in southwestern Minnesota, but also scattered elsewhere in the state, are Cretaceous sandstone aquifers that are interbedded with thick shale. These sandstone aquifers are relatively thin and only locally useful.
Figure 4. Unconsolidated aquifer types.
Layered above bedrock nearly everywhere in the state are unconsolidated sediments deposited by glaciers, streams, and lakes. These sediments are shown in tan and brown on the cross sections (Figure 2). In the unconsolidated sediments setting, aquifers are surficial or buried sand and gravel that usually occur only locally. The state can be divided into three regions based on sediment composition and thickness (Figure 4).
In the northeast and southeast, unconsolidated sediments are generally thin or absent. The major river valleys in these regions are an exception, as these river valleys do contain sufficiently thick sediment for useable unconsolidated aquifers. In central and east-central Minnesota the unconsolidated sediments are relatively sandy and aquifers are more common. In the remainder of the state, sediments are relatively clayey and aquifers are less common.
Figure 5. Groundwater provinces.
Combining the regions of the two general geology settings in Figures 3 (bedrock) and 4 (unconsolidated sediment) creates the groundwater provinces shown in Figure 5.
Provinces 1 and 4 (metro and central, respectively) are characterized by buried sand aquifers and relatively extensive surficial sand plains as part of a thick layer of unconsolidated sediments deposited by glaciers overlying the bedrock. Province 1 is underlain by sedimentary bedrock that has good aquifer properties, but in Province 4 the glacial sediments are thick, sand and gravel aquifers are common, and the deeper fractured bedrock is rarely used as an aquifer.
The unconsolidated glacial sediments of Provinces 2 and 5 (south-central and western, respectively) are typically clayey and may contain limited extent surficial and buried sand aquifers. In Province 2 the sedimentary bedrock aquifers are commonly used, but in Province 5 the fractured bedrock is usually buried deeply beneath glacial sediments and is only locally used as an aquifer.
The unconsolidated sediments in Provinces 3 (southeastern) and 6 (arrowhead) are thin or absent and, therefore, not used or relatively unimportant, except in major river valleys where sediment thickness is greater. However Province 3 is underlain by productive bedrock aquifers, but Province 6 is underlain by hard fractured bedrock that typically has limited groundwater yield.
Each of the provinces has a unique combination of aquifer characteristics that affect water availability. Table 1 shows general groundwater availability by province for different groundwater sources. The table shows that some parts of the state have several groundwater resources to choose from, while other parts of the state may have only limited groundwater resources available. Water resource planners, managers, and users should recognize these differences when evaluating groundwater resources for future use.
- Quaternary Geology - General
- Quaternary Geology - Detailed
- Bedrock Geology - General
- Bedrock Geology - Detailed
- Depth to bedrock
- Digital Elevation Model (DEM)