PREDICTING THE LOCATION OF DISCHARGE OF FLOODING ABANDONED MINES

Most underground Pittsburgh mines are down-dip, meaning that mining is generally advanced from shallow to deep, and below regional drainage elevations. Prior to 1990, a large number of underground mines in the basin had already been abandoned nearly all of which have been confirmed to be "flooded." Since 1990, several more mines have been abandoned and show water levels that are thought to still be rising.

It would be beneficial both environmentally and economically to know where and when discharges from flooded abandoned mines will occur. It would also be beneficial to know what the water quality and quantity will be.

Approximately 10 underground coal mines within Pittsburgh coal (Pennsylvanian) of northern WV-southwestern PA, from 800-2200 hectares in area, are in the process of flooding following mine abandonment between 1986-1995. The flooding history of two mines within this group between 1988-2001 is compared to examine hydrogeologic factors influencing flooding rate and ultimate discharge location. Both mines are similar in area, depth, size, age, and mining methods employed. Both outcrop along the Monongahela River and extend down-dip for approximately 12 km. Both have narrow slope main entries close to the outcrop, which pose a special risk during flooding because they might accelerate the rate of water level rise. The first mine (Mine A) is bounded by a flooded mine to the south that is held at constant head by pumping; on the north by a nearly dry mine just beginning to flood. It flooded from 1994-2000 without pumping. However, as groundwater approached the mine opening, the flooding declined in rate and gradually halted, reaching a steady state water level. Mine B, bounded by flooding mines to both north and south, has been gradually flooding since 1988; as of 2001 it is about 60% flooded. The major contrasts between the 2 mines are (a) flooding rate--Mine A flooded much faster and (b) ultimate location of discharge--Mine A stabilized without external control while Mine B did not and continues to flood. These results indicate the importance of regional hydrogeological context on the flooding history of individual mines. The behavior of Mine A may be extrapolated to Mine B, which is expected to discharge to an abutting mine at some time before 2005 and to discharge to the surface through that mine.