| Abstract |
Drainage from abandoned underground coal mines negatively impacts many miles of stream habitat throughout the Appalachian region. The drainage is commonly called acid mine drainage (AMD) due to its low pH; however, not all mine drainage is acidic. The quantity and quality of the water discharged from a coal mine depend upon numerous variables, such as the design of the mine, chemical composition of the coal and surrounding rocks, and local climate. Coal extracted from the now-abandoned Cherry Valley Coal Mine near Leetonia, Ohio, was reached by a slope entry such that the mine is not entirely up-dip, and a significant area is flooded. Recharge water that enters the unsaturated area of the mine mobilizes soluble iron-sulfate salts as it flows down-dip and adds pyrite oxidation products to the mine pool. The bedrock overburden is covered by calcareous glacial till that imparts alkalinity to the shallow groundwater, buffers the acidity, and keeps the pH inside the mine circumneutral. Maintaining a circumneutral pH reduces pyrite oxidation by decreasing the solubility of ferric iron, the primary oxidizing agent of pyrite at low pH, which reduces the positive feedback mechanism that drives pH down and concentration of oxidation products up. Shallow groundwater is brought to the mine via subsidence fractures, which facilitate a rapid increase in discharge from the mine (and dilution of oxidation products) in response to surface runoff events. The loadings of all dissolved ions, except iron, are controlled by the changes in discharge rather than the changes in concentration.
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