TRACE METAL AND STABLE ISOTOPE CHARACTERIZATION OF LOW-FLOW ACID MINE DRAINAGE (AMD) SEEPS IN INDIANA

Three abandoned coal mining sites in southwest Indiana are being considered for the installation of passive remediation systems. At each site, acidified (pH <2-3) waters emanating from low-flow seeps will be treated using a constructed sulfate-reducing bioreactor cell (SRBC) consisting of well-mixed compost, limestone gravel, and straw. The purpose of this study is to characterize the pre-existing conditions at each of the sites prior to construction of the treatment systems. Analysis of the d³⁴S (sulfate, sulfide, and elemental sulfur) and d¹⁸O (water and sulfate) will be used in combination with vadose-zone hydrology and trace metal chemistry data to identify the contribution of sulfate from precipitation interacting separately with mine tailings and spoils before mixing and eventually discharging at the seeps. Additionally, the rate and extent of microbial activity related to sulfate generation will also be resolved from this information. These data will also allow engineers to determine the size of SRBC needed to achieve a specified effective lifespan before the useful capacity of the cell is exceeded. For comparison purposes, a constructed wetland built in 2004 to contain runoff from a mine tailings pile will be monitored using the same methods. Preliminary results indicate that the wetland may be behaving similar to a SRBC in terms of alkalinity generation and decreasing trace metal concentrations. The characteristics and environmental impact of acid mine drainage (AMD) seeps at these sites are similar to those of numerous other sites in the Midwest and will provide information applicable to a significant number of low-flow AMD discharges throughout the region.