INTERRUPTION OF FLOODING TO DEWATER UNDERGROUND MINES OVER THE FLOODED PITTSBURGH COAL: SOUTHEASTERN MONONGAHELA BASIN

Coal mining in the Upper Pennsylvanian Monongahela Group of the southeastern Monongahela basin (from Waynesburg, PA south to Clarksburg, WV) is mainly in the Pittsburgh coal but also in the Sewickley coal seam. The Pittsburgh coal is the most extensive and productive in the Monongahela Basin. Although not as extensive, the Sewickley coal approximately 30 m above the Pittsburgh is intensively mined in the Morgantown, WV area. Most of the shallow portions of the Pittsburgh coal have been mined out and current mining is in the deeper central portion of the basin. Mining in the Sewickley continues in several deep as well as surface operations. Nearly all Pittsburgh mines ceased water extraction within the last 15 years or earlier and their works flooded to near equilibrium resaturation by 2003. The flooded mines in this district either discharge to surface waters (pre-SMCRA) or are pumped to treatment plants to maintain mine water levels below surface water elevations. In response to renewed mining in the Sewickley seam in 2003-06, previously-flooding Pittsburgh workings were pumped to dewater overlying Sewickley mines. Mine water is in several locations pumped from one mine to another across an intact barrier to divert water to distant treatment plants. Lowered potentiometric levels resulting from this pumping allow reentry to previously-flooded Sewickley workings. Monitoring of mine-water elevations during pumping across barriers has yielded information on the hydrogeologic properties of the coal mine aquifer, including heterogeneity in hydraulic conductivity and local artesian storativity. This pumping has reversed an earlier “natural” trend of resaturation of closed workings and underscores that mine-water reservoirs are productive aquifers that may be manipulated using large-scale pumping.