M.S. (Master of Science)
Department of Geology
Aquifers--Illinois--Mount Carmel Region; Hydrogeology--Illinois--Mount Carmel Region; Longwall mining--Illinois--Mount Carmel Region; Sandstone--Illinois--Mount Carmel Region
The physical hydrogeology of the Mt. Carmel Sandstone Aquifer overlying and surrounding portions of a high extraction coal mine was investigated during this study. Subsidence of the Mt. Carmel Sandstone and adjacent strata overlying the mine has occurred approximately four years prior to this study. After subsidence, it was hypothesized that the confined Mt. Carmel Sandstone aquifer had become an unconfined, leaky-confined, layered, double porosity, or bounded aquifer. Five pumping tests were performed to test each of these aquifer models. A composite section of two permeable units within the Mt. Carmel Sandstone was pumped during the first three tests. The lower permeable portion of the Mt. Carmel Sandstone was pumped discretely during the remaining two tests. Analysis of static and dynamic heads indicated that the two sandstone units comprised distinct hydrogeologic units. These units were informally designated the upper and lower Mt. Carmel Sandstones during this study. Drawdown data were evaluated for double porosity behavior and the effect of linear discontinuities using published analytical solutions. This analysis indicated linear discontinuities were responsible for the characteristic drawdown response. Numerical modeling was performed to test this conclusion. A transient, two-dimensional numerical model of the lower Mt. Carmel Sandstone was developed and calibrated against pumping test data. The model simulated the aquifer as three homogeneous zones separated by two linear discontinuities. The first zone represented the area overlying the interior of the mined panel and was characterized by moderately (i.e.? 1 to 2 orders of magnitude) increased permeability and storativitv relative to the pre-subsidence condition. The second zone represented the portion of the aquifer over the margin of the panel and was characterized by significantly (i.e., 3 to 4 orders of magnitude) increased permeability and storativity relative to the pre-subsidence condition. The third zone represented aquifer away from the subsidence area. The results of the model support the linear discontinuity conceptual model of the effects of subsidence on the Mt. Carmel Sandstone. Development of linear discontinuities may occur in other hydrogeologic settings as a result of anthropogenic factors (e.g., subsidence) or natural factors (e.g., faults and lithologic changes).
Miller, Joseph D., "Hydrogeologic characterization of a heterogeneous sandstone aquifer overlying a high extraction longwall coal mine" (1996). Graduate Research Theses & Dissertations. 3429.
xv, 205 pages
Northern Illinois University
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