Abstract

A method is demonstrated to employ combined mapping and field techniques to unravel complexities in the hydrogeology of flooded and unflooded underground coal mines of shallow (<120 m, <400 ft) depth. For a study area in the Appalachian coal basin, underground mines, coal outcrop, coal structure, and mine-drainage discharge locations were mapped onto an integrated geographic information system platform. The Upper Freeport coal seam (Allegheny Group) in the study area is relatively shallow (<120 m, <400 ft), with many closed free-draining mines and numerous discharges. The mapping of coal outcrop and structure was accomplished using (1) high-resolution aerial orthophotographs, (2) digital outcrop polylines, and (3) a coal-bottom structure surface created by geospatial interpolation of point data mostly abstracted from original mine maps. Mapping results integrated with field measurements of mine-water discharge allow inference of likely pool locations and potential interconnections between underground workings, which are not apparent from mine maps alone. The results are reconnaissance level in that the interpreted pool locations and depths are unconfirmed by drilling or water level measurement; therefore, any action based on such results should be preceded by fieldwork to confirm hypotheses offered by the reconnaissance analysis. Nonetheless, such a preliminary interpretation of hydrogeological conditions based on little or no subsurface (well) water level information may be highly useful for both interpreting subsurface conditions and for planning future research. The technique is based on a combination of mine mapping, digital analysis of geologic structure, and surface reconnaissance fieldwork. Results are directly applicable to areas of reclamation of shallow coal mining where mine closures have resulted in an uncontrolled discharge of mine drainage.

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