GEOSTATISTICAL RECONSTRUCTION OF MINING HYDROGEOLOGY IN THE UPPER FREEPORT COAL, WV-MD

The Upper Freeport coal seam (Pennsylvanian, Allegheny Group) forms an extensive mining district in northern West Virginia and western Maryland. Most underground mines are above regional drainage, closed or abandoned, and discharge acid mine drainage to the Cheat, Blackwater and Potomac basins. The purpose of this study was to apply geostatistical tools to create a digital model of coal geology and to use this product to constrain mining hydrogeology. Data from legacy mine maps and field observations were used to (1) reproduce the geologic structure of the coal bed, and (2) delineate mine aquifers, flooded and non-flooded. Underground mines maps were compiled, georeferenced and digitized onto1: 24,000 scale sheets. Coal bed elevation survey data were sampled from these and interpolated by ordinary kriging to produce a structure contour grid at a 3-meter cell size. A coal outcrop polygon was derived from intersection of this structure grid with a 3-meter DEM. The mine maps, structure contours and outcrop were projected using elevation points of mine discharges to delineate mine pool areas. The majority of mines in the study area are free-draining and largely unflooded. Underground mining was focused in large synclines, and the mine pools that do occur are found along their down-dip limbs. Stream geomorphology is strongly influenced by regional structure. Major rivers paralleling synclinal axes are the focus for impacted tributaries transporting AMD in a down-dip direction. Thus the pattern of AMD discharges and stream water contamination is the synthesis of geologic structure, location of streams collinear with synclinal axes, and distribution of underground mines focused on synclinal axes.