Aquifers in General

Before the first glaciers came into Illinois, bedrock formed much of the landscape. Ancient rivers cut valleys into the bedrock surface. These valleys were subsequently filled with layers of geologic materials (sand, gravel, silt, and clay) that were deposited by successive advances and retreats of glaciers. Later glacial advances deposited material on top of that left by earlier advances. With each successive glaciation, new layers were deposited until today we have as much as 400 to 500 feet of these materials between the current land surface and bedrock.

Below the water table (generally 5 to 50 feet below land surface) these layers are saturated with ground water. Water exists in the pore space between the soil particles. Layers of geologic material that can provide a useable, sustainable supply of water to a well are called aquifers. Aquifer materials usually consist of porous sand and gravel in glacially deposited materials and generally either sandstones or fractured rock in bedrock. Other materials, like clay, silt, and shale (a type of bedrock), are not aquifers because water moves so slowly through them that a useable quantity of water cannot be withdrawn from a well.

The Mahomet Aquifer

The Mahomet aquifer is one of the largest groundwater resources in the state. Below are described the features of the Mahomet aquifer, its geology, its ground-water flow system, ground-water use in the region, other specific information about the system, and projected use in the future.


• History
  (under development)
• Geology
  The ISGS and USGS recently completed mapping the Quaternary sediments (the sediments from the ground surface to the top of the bedrock) in east-central Illinois. These maps cover 4,000 square miles and include all or portions of Champaign, DeWitt, Ford, Iroquois, Logan, Macon, McLean, Piatt, Sangamon, Tazewell & Vermilion Counties. To view these maps, see USGS Map I-2669.
  
  These maps cover a large portion but not all of the area overlying the Mahomet aquifer.
  
  
• Ground-Water Flow
  (under development)
• Ground-Water Withdrawals
  (under development)
• Ground-Water Chemistry
  (under development)
• Potential Future
  (under development)
• Other Useful Information
  (under development)

The Role of Aquifers Above the Mahomet Aquifer

(under development)

The Role of Bedrock Aquifers

(under development)

Last Updated: September 29, 2000
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