Ground-water samples were collected from 459 wells located in the Michigan basin as part of a Regional Aquifer-System Analysis. Data on the physical and chemical characteristics of 476 ground-water samples from these wells represent ground-water characteristics in the Berea Sandstone, Coldwater Shale, Marshall Sandstone, Michigan Formation, Bayport Limestone, Saginaw Formation, Grand River Formation, and glacial deposits. Ground-water samples were measured in the Geld for specific conductance, temperature, and alkalinity. Analyses of ground water for concentrations of dissolved oxygen, ferrous iron, total iron, and sulfide were also done in the field. Additional laboratory analysis provided data on eight major and 18 minor inorganic constituents. Twenty-one samples were analyzed for tritium, 140 samples were analyzed for carbon-13, and 19 samples were analyzed for carbon-14. The stable-isotope ratio of deuterium to hydrogen was determined for 408 samples; the ratio of oxygen-18 to oxygen-16 was determined for 433 samples; and the ratio of sulfur-34 to sulfur-32 was determined for 20 samples. Sixteen samples were analyzed for the unstable isotopes of uranium; 13 samples were analyzed for radium-226; and the ratio of radium-228 to radium-226 was determined for 13 samples.
