Use of O and S Isotopes to Define Sources of Water and Sulfate in Acid Mine Drainage Waters

Coal mining in Maryland, West Virginia, Pennsylvania, and other states has resulted in acid mine drainage problems in rivers throughout the region. The underground workings at the Kempton Mine have been abandoned since the 1950's, and the water filling these mines is discharged at a rate of 6,000,000 gallons per day into the headwaters of the Potomac River. This water has an average pH of 3.0 and an average dissolved load of 1 g/L. Evaluation of the mitigation options requires identification of water and acidity sources. We are using isotopic compositions of mine drainage waters to define hydrologic sources, flow paths, and acid sources. Water samples were taken monthly of mine water and other local sources. Oxygen isotope analyses are conducted on these samples. Seasonal variations in δ ^{18}O composition of mine drainage would suggest significant rapid meteoric input. Little or no variation in \delta¹⁸O composition would suggest that mine drainage is derived primarily from groundwater sources or that the residence time in the mine is long. Sulfate precipitated as barite from these samples is analyzed for δ ^{34}S and \delta¹⁸O. There is significantly more sulfate in the mine drainage waters than there is iron. The isotopic signature is used to determine whether the sulfur source is pyritic or organic. Sulfate δ ¹⁸O data are used to distinguish between sub-aerial and sub-aqueous oxidation of sulfur.