Reports
Hydrologic and mining data from an area of undergound coal mining in Garrett County, Maryland
1988, Hiortdahl, S.N.
Report of Investigations 41A
Abstract
This report is the second in a series of reports describing the hydrologic conditions in an area of underground coal mining in southwestern Garrett County, Maryland. Hydrologic and mining data collected during the second study phase (October 1981 to September 1984) are presented, and changes in mining activity and hydrologic conditions between the first and second study phases are briefly noted.
Three adjacent permit areas were mined using the room-and-pillar method. Coal extraction within the three permit areas was about 50 percent complete by the end of 1984. The cumulative area undermined increased from about 650 acres in July 1981 to about 1,650 acres by July 1984. Total annual pumpage of mine-drainage water increased from 410 to 660 million gallons per year during the same period.
Water levels in several observation wells above the mines have declined from tens to hundreds of feet. Water-level declines ranging from about 400 to 450 feet occurred in two undermined wells open to a confined zone immediately above the mine. Long-term water-level declines occurred in two wells that are open to a confined zone below the mines.
Discharges of treated acid-mine drainage raised the specific conductance in South Fork Sand Run and contributed about 19 to 44 percent of the daily flow at the gage. The effect was less obvious in Laurel Run, because the volume of treated acid-mine drainage discharged there comprised only about 3 to 4 percent of the daily flow at the gage.
Several main-channel segments of Laurel Run lost streamflow to the local ground-water system. Periodic streamflow-seepage measurements conducted between 1980 and 1984 indicate that the location and magnitude of the stream-channel seepage losses varied from year to year.
