Maryland Department of Natural Resources


First report on the hydrologic effects of underground coal mining in southern Garrett County, Maryland

1985, Duigon, M.T. and Smigaj, M.J.

Report of Investigations 41


Recent increased demand for coal is expected to increase surface and underground mining activities in the coal basins of western Maryland. This report describes preliminary findings on the hydrogeologic system in southwestern Garrett County, Maryland, where a large underground coal-mining operation had recently begun . A network was established to gather streamflow, water-level, and water-quality data. It is presently planned to continue data collection throughout the period of mining and reclamation.

Shallow (less than about 100 feet deep), intermediate (about 100 to 400 feet deep), and deep (greater than about 400 feet deep) ground-water flow systems are present in the study area, and all are characterized by low, secondary permeability. Hydraulic conductivity (less than 2 feet per day) of the shallow system is about two orders of magnitude greater than the deeper systems. Deep ground-water flow is part of a regional system whose boundaries are miles beyond the study area. The base of the fresh ground-water system was found at one site in the study area at a depth of 940 feet below land surface.

Drainage from earlier mining activities was found to contribute substantially to surface-water quality. Measurements of pH in Laurel Run ranged from 2.4 to 3.8, dissolved aluminum ranged from 1.7 to 6.9 milligrams per liter, and dissolved sulfate ranged from 42 to 250 milligrams per liter. The North Fork and the South Fork of Sand Run were less severely affected by earlier mining; however, the South Fork was receiving about 1 million gallons per day of treated acid mine drainage from the current mining operation.

Well-water samples and a sample collected inside the mine had pH values above 6 and generally low levels of dissolved solids. Samples collected from underground-mine discharge points had low (2.6 to 4.0) pH and high (1,000 to 3,430 milligrams per liter residue) dissolved-solids content.

Dewatering of the underground mines has affected ground water and surface water in the study area. Water levels at one cluster of observation wells dropped from 77 to 350 feet as mining approached to within several hundred feet of the cluster. Total runoff in the Laurel Run basin decreased as mine dewatering occurred in the basin. Discharge of water pumped from the mines into South Fork increased total runoff in that basin.