Introduction: The U.S. Geological Survey began a study in 1980 of the quality of water in the 14 principal aquifers in Minnesota. The U.S. Environmental Protection Agency funded the study as part of the Underground Injection Control Program, which deals with disposal of liquid wastes beneath land surface. The initial report designated the 14 aquifers and provided general information about their geologic, hydrologic, and water-quality characteristics (Adolphson and others, 1981). This report, one in a series that describes individual aquifers in more detail, concerns the Upper Carbonate aquifer.