HYDROGEOLOGY OF UNDERGROUND MINES IN THE UPPER FREEPORT COAL SEAM, NORTHERN APPALACHIAN COAL BASIN

The Upper Freeport coal seam (Pennsylvanian, Allegheny Group) of West Virginia, Pennsylvania, and Maryland is largely mined-out with many closed, above-drainage mines that are discharging acid mine water. Active and passive remediation methods in the Cheat, Blackwater, and Potomac basins are actively being implemented, yet generally lack a firm hydrogeological basis for planning and design of water treatment. The purpose of this study is to develop the hydrogeological framework for these closed mines and to relate this to observed discharges and water chemistry in the basin. Geographic information system (GIS) technologies were utilized to map coal bed structure and outcrop, to spatially reference scanned mine maps, and to visually map and illustrate flooding levels within abandoned mines. A general understanding and protocol for mapping the hydrology of underground above-drainage mining is the primary result.

Field data required for mapping discharges included GPS locations, measurement of flow rate and screening-level water chemistry (pH and specific conductance). Areas of potential discharge were identified using topographic maps, coal bed structure and high-resolution digital aerial photography. Specific discharges were verified by walking stream channels to identify tributary inflows. Discharge locations were linked with individual mines mapped by GIS methods, including both surface and underground mines. Discharge elevations were also used to estimate flooding levels assuming little head loss during flow through these transmissive mine-collapse deposits.

Mine discharges are generally found along the coal outcrop in close proximity to a tributary. Surface contour mines are on the order of 10-30 acres and typically generate numerous low flow discharges that are independent of coal bed structure. Shallow underground mines range from about 80 to >300 acres and have fewer discharges with higher, more perennial flow rates. The magnitude of the acid mine drainage problem in the study area has resulted in one of the most intensive reclamation efforts in the Appalachian Coal Basin.