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Deep Creek Lake in Garrett County, Maryland drains an area of about 65 square miles. There is concern that acid rain combined with acid mine drainage from coal mining in the basin will exceed the capacity of the lake to buffer the acid input from these sources. This study was done during 1983 to determine the sources of alkalinity to the lake f and to make a rough estimate of the amount of alkalinity that enters the lake from six streams that drain carbonate and noncarbonate bedrock formations. Bedrock in the basin is predominantly sandstone and shale of Devonian to Pennsylvanian age. The Mississippian Greenbrier Formation, which crops out in 5 percent of the basin, is the only calcareous rock unit. Four streams draining the Greenbrier and two streams draining noncarbonate formations were sampled to assess the contribution of alkalinity to Deep Creek Lake. The average annual alkalinity of six sampled streams ranged from 7.6 to 36.8 tons per year per square mile of drainage area. The average total alkalinity contributed to Deep Creek Lake by these streams is 161 tons per year as calcium carbonate. Mass-balance calculations based on very limited data indicate that this alkalinity is derived from both carbonate rocks (Greenbrier Formation) and from weathering and hydrolysis of silicate minerals. Other sources may contribute alkalinity to Deep Creek Lake, but could not be quantified within the scope of this study. No changes in stream water quality were found that could be directly attributed to the stream having crossed the boundary from one noncarbonate bedrock formation to another. Inflow to streams from adjacent or underlying carbonate bedrock was apparent in several streams from increased values of pH and conductance. INTRODUCTION Study Background There is concern that acid rain combined with acid mine drainage from coal mining will exceed the ability of Deep Creek Lake (fig. 1) to buffer the acid input from these sources. A study is presently being made by Martin Marietta Corporation/ and Garrett Community College to determine the magnitude of these acid inputs. Preliminary results of their study show that/ although the acid input is considerable/ alkalinity in the lake has remained almost constant. Reports from this study include Scott and others (1982)/ Campbell and others (1983), Ferrier (1981), and Ferrier and Risoldi (1983). The U.S. Geological Survey, in cooperation with the Maryland Power Plant Siting Program, has undertaken the study reported herein to investigate the contribution of alkalinity from the Greenbrier Formation to Deep Creek Lake. This formation is the only bedrock in the drainage basin of the lake that contains limestone (carbonate). Purpose and Scope Specific objectives of this report are to (1) describe the chemical quality of base flow in streams that drain the Greenbrier Formation, (2) make a rough assessment of the amount of alkalinity contributed by the Greenbrier Formation to Deep Creek Lake, and (3) determine if changes in chemical quality of base flow occur when a stream crosses several geologic formations. Six streams that enter Deep Creek Lake were selected for study in order to meet the above objectives. Four of the streams drain the Greenbrier Formation; one stream drains the Mauch Chunk Formation that directly overlies the Greenbrier Formation and was reported by Ferrier (1981) to contain alkalinity values above those of other noncarbonate formations; and one stream drains the Jennings, Hampshire, and Pocono Formations. The investigation included 648 in-stream measurements of temperature, conductivity and pH at 216 sites/ 28 field determinations of alkalinity/ and 18 streamflow measurements. Water samples from six streams and five groundwater wells were analyzed for major ions by the U.S. Geological Survey laboratory in Doraville/ Ga.

Estimated average annual alkalinity of six streams entering Deep Creek Lake, Garrett County, Maryland