A RE-EVALUATION OF CONTROLLING FACTORS OF PENNSYLVANIA'S COAL MINE DISCHARGE GEOCHEMISTRY

Abandoned mines, with their drainage systems no longer intact or functioning, create the aqueous and oxidizing environment required for acid and metals to leach from the remaining rock and drain into nearby waterways. In Pennsylvania alone there are over 3,000 miles of streams contaminated by drainage from abandoned coal-mine discharge (CMD). Toxic metals in CMDs cause environmental impairment by killing plant and animal species, reducing biodiversity, disrupting the food chain, destroying the buffering capacity of water bodies, and altering vital habitats. In 1999, the United States Geological Survey (USGS) collected water samples from 143 CMD sites in the Anthracite and Bituminous Coalfields of Pennsylvania (Cravotta, 2008). Unfiltered samples were used to determine alkalinity, and filtered samples were used for cation and anion analysis. Complete hydrologic and inorganic aqueous geochemical data were compiled to identify the primary controls on geochemistry and pH: 1) dilution by neutral to alkaline waters, 2) solubility of hydroxide, sulfate, and carbonate minerals, and 3) complexation and adsorption of aqueous sulfate.

Thirteen years have passed since the USGS study was conducted, during which time the oxidation and dissolution of minerals into the mine outflows has continued. Water quality data and water samples were resampled from the same CMD sites during the summer of 2012. Chemical analysis and field measured water quality parameters are used in geochemical models to evaluate controls on ion mobility. Our overall goal is to determine whether the controlling factors on CMD geochemistry have changed over time.