MODELING THE LEACHING PATTERNS OF CENTRAL APPALACHIAN COAL MINE SPOILS

Surface coal mining in Appalachia, USA has numerous environmental impacts on waters draining from mining-influenced areas. The interaction of rainwater with mine spoils results in rapid spoil weathering and generates salts of mineral origin that leach to streams. These salts are collectively termed total dissolved solids (TDS) and are typically dominated by SO₄^2-, HCO₃^-, Ca²⁺, Mg²⁺ and other ions including trace elements such as As and Se. Higher TDS concentrations in mine drainage waters may lead to altered aquatic macroinvertebrate communities, thus improved understanding, modeling, and prediction of potential ion release patterns to drainage waters will enable improvement of mining-influenced stream water quality. For this study, 39 Appalachian surface coal mine spoils were placed in columns and sequentially leached with 2.5cm of simulated rainwater. Collected leachates were analyzed for pH, specific conductance (a proxy variable for TDS), and major and minor ions. A five-parameter nonlinear regression was developed to model spoil leaching patterns. Leaching patterns for most ions were high in leachate concentrations initially, decayed exponentially to a breakpoint, then became linear in subsequent leaches. Most major ions tended to either stabilize or continued to decline in concentration at the end of the leaching period, whereas most minor ions tended to decrease to below detection limits early in the leaching process. Exceptions to this pattern included bicarbonate, which generally increased in concentration throughout the leaching period, and iron, which had a random leaching pattern that was unable to be modeled. Results indicated that spoil leaching patterns were influenced by both spoil rock (mudstone, mixed rock, sandstone) and weathering (unweathered or weathered) type. Weathering type tended to influence the initial and final leachate concentrations, whereas rock type tended to influence the rates of ion release from the mine spoils. Overall, results are intended to improve future mine spoil handling and management techniques.