A coal deposit in Bay County, Mich., typical of Pennsylvanian-coal deposits in the State, was studied to determine the degree to which hydrologic factors might affect future coal mining. The coal deposit, which averages about 0.5 meters in thickness, lies 50 meters below land surface. It is part of a multi-layered aquifer system that contains sandstone, shale, sand and gravel, and clay units in addition to beds of coal. Hydrologic characteristics (hydraulic conductivity and storage coefficient) of each unit were evaluated by analyses of aquifer tests and a finite-difference groundwater flow model. A model simulating groundwater flow to a hypothetical mine was developed. Results of the study indicate that seepage will probably not be great enough to preclude mining coal. Also, pumping water to keep the mine dry will have little effect on heads in aquifers outside the mine during the first decade of mining.
Although coal was mined in Michigan during 1860-1950, significant reserves remain. These deposits, part of the Saginaw Formation of Pennsylvanian age, are near the industrialized parts of the State. The quantity of pumped water needed to keep mines dry and the effect of pumping on aquifers surrounding the mines is a major factor in determining the feasibility of opening new mines.
