Quaternary glacial deposits and Pennsylvanian and Mississippian sandstones, -the Saginaw Formation and Marshall Sandstone- are the major aquifers in the Michigan basin. These aquifers supply approximately 188 million gal/day to municipalities in the 29 ,000 sq mi study area. The most significant problems related to groundwater supplies are the identification of potable sources of groundwater in large quantities and the migration of saline groundwater toward pumping centers. Saline water underlies the entire lower Peninsula of Michigan at indeterminate depth in the deeper parts of the Saginaw Formation and Marshall Sandstone in the center of the Michigan basin. In places, saline water is present in glacial deposits. Overdraft has resulted in severe drawdown in the Lansing area and the abandonment of wells near Flint because of saline water encroachment. Increased demand on the groundwater resources of the study area are expected to cause further problems.
In 1985, the U.S. Geological Survey began a 5-yr study to define the geohydrologic framework, describe the geochemistry of groundwater in the glacial and bedrock aquifers, and analyze regional groundwater flow patterns. The scope, plan of study, organization and work elements are described in this report.
