Tracing interaction of acid mine drainage and coal combustion byproducts in a grouted coal mine: Application of strontium isotopes

Tracing interaction of acid mine drainage and coal combustion byproducts in a grouted coal mine: Application of strontium isotopesBarbara L. Hamel, MSUniversity of Pittsburgh, 2005The inactive Omega Coal Mine in Morgantown, West Virginia was partially grouted in 1998 by injection of coal combustion by-products (CCB) in order to ameliorate acid discharge; but discharge continued with little measurable change. In this study, discharge chemistry and strontium (Sr) isotope ratios were determined to identify and quantify the extent of interaction between mine waters and the CCB material used to grout the abandoned mine.Eight sampling sites were monitored around the downdip perimeter of the mine. The major and trace element chemistry of the discharges was not generally sufficient to differentiate between discharges that interacted with grout and those that did not. Elements that showed the most separation include potassium and arsenic, both of which were elevated in the waters that interacted with CCB grout. In contrast, the Sr isotope ratios were clearly able to distinguish between discharges from grouted and non-grouted areas. Discharges without exposure to the grout had 87Sr/86Sr ratios ranging from 0.7151 to 0.7159, while two discharges that interacted with grout had ratios in the range of 0.7140 to 0.7146. The Treatment Inlet, which includes both grouted and ungrouted discharges, yielded intermediate isotopic ratios. Leaching experiments on CCB grout, coal, and surrounding rock formations are consistent with the isotopic trends observed in the discharges. Based on these results, waters that interacted with grout received 30-40% of their Sr (and Ca by assumption) from the CCB grout material. This novel application of Sr isotopes illustrates their ability to track fluid flow paths in grouted mine systems