Details of water-bearing units, including a generalized potentiometric surface, are derived from logs of more than 4,200 wells along 3,500 miles of section lines. Hydrogeologic sections are spaced 6 to 20 miles apart. Aquifer maps are based on information from hydrogeologic sections and from previous studies. Where a type of aquifer was less than 15 square miles in areal extent, it was not mapped because of scale limitations. Types of aquifers depicted in the illustrations include unconsolidated and bedrock aquifers.
Unconsolidated aquifers are the most widely used aquifers in Indiana.
Types of unconsolidated aquifers include surficial, buried, and discontinuous layers of sand and gravel. Most of the surficial sand and gravel is located in large outwash plains in northern Indiana and along the major rivers in the southern two-thirds of the State. Buried sand and gravel aquifers underlie much of the northern two-thirds of Indiana, where they are typically interbedded with till deposits and can be 10 to 400 ft deep. Discontinuous sand and gravel deposits are present as isolated lenses, primarily in glaciated areas. Wells completed in the bedrock aquifers generally have lower yields than wells in most of the sand and gravel aquifers, but the bedrock aquifers are areally widespread and a major source of water for many domestic users and some large users of ground water.