Trace Element Partitioning in Ground Water at an Abandoned Mine-Land Site Reclaimed with Coal Combustion Products

In Pike County, Indiana, an abandoned mine-land site generating acid-mine drainage was reclaimed using coal-combustion products as fill and cap material. Concentrations of several trace elements were monitored in ground water on a quarterly basis over a period of four years. Pre-reclamation monitoring established that the trace elements arsenic, cadmium, chromium, copper, lead, nickel, and zinc occurred in higher concentrations in acidic waters (pH < 4) than in waters more nearly neutral. The trace element boron occurred in low concentrations (<1 mg/L) throughout the study area while barium, mercury, and molybdenum were at or below detection limits in all water samples. Only arsenic, boron, and molybdenum increased in concentration after reclamation. Arsenic levels remain highest in acidic ground water, but also occur above pre-reclamation levels in some monitoring wells in close proximity to coal-combustion products. The highest boron and molybdenum levels occur in wells screened in fill material close to a fixated scrubber sludge cap. High concentrations of iron limit molybdenum solubility due to coprecipitation, inhibiting dispersion of molybdenum through the ground water. Boron mobility does not appear to be constrained like molybdenum and is more widely dispersed in ground water.