Migration of mineralized water from abandoned subsurface coal mines in Monitor and Williams Townships was thought by many residents to have affected the quality of domestic ground-water supplies in the area. To investigate the possibility, wells were installed to obtain geologic data and water samples for chemical analysis; analysis also was made of concurrent related data collected by other agencies.
The principal rock units are glacial deposits and the Saginaw Formation. Glacial deposits, 75 to 175 feet thick, are primarily clay underlain in places by sand and gravel. This sand and gravel is the primary source of ground water. Underlying the glacial deposits is the Saginaw Formation--a unit that is mostly shale and silty shale containing beds of siltstone, sandstone, and coal.
Specific conductance of water from wells indicate that dissolved-solids concentration increases with depth. About 50 percent of specific conductance values of water from wells more than 100 feet deep were equal to or greater than 5,000 microsiemens, whereas only 13 percent of the values of water from wells less than 100 feet deep were equal to or greater than 5,000 microsiemens.
Results of chemical analyses indicate no apparent correlation between concentration and source for most constituents. Plots of chloride/sulfate ratios versus specific conductances indicate that water from the Saginaw Formation is as likely to influence the quality of water in glacial deposits as is water from abandoned mines.
