ACCUMULATION OF HEAVY METALS IN SEDIMENTS FROM A WETLAND SYSTEM CONSTRUCTED TO TREAT ACID MINE DRAINAGE: PRELIMINARY RESULTS

The campus of the University of Virginia's College at Wise (UVa-Wise)is affected by acid mine drainage as a result of two decades of strip mining. Acid mine drainage is remediated using a passive wetlands treatment system. The Wise Formation was the host rock for coal extracted on the UVa-Wise campus. These rocks include significant thicknesses of metalliferous black shale, a potential source of heavy metals that may accumulate in wetlands sediment. To determine if heavy metals are accumulating in wetlands sediments, we collected samples from twelve locations in the system and used a sequential extraction to solvate heavy metals. We used ICP to determine metal concentrations. We found elevated concentrations of As (1-12 ppm), Ni (2.5-49 ppm), Pb (10-144 ppm), Zn (56-330 ppm), Cu (13-72 ppm), Cd (1-11 ppm), and Co (17-168 ppm). Levels of these metals are elevated by a factor of 2.5 (Ni) to 5 (Co) relative to sediments collected from watersheds that are not affected by acid mine drainage. It is likely that low pH fluids associated with acid mine drainage enhance metal movement, resulting in concentration of metals in sediments accumulating in the wetland treatment system. Because the design lifespan of the system is twenty to thirty years, sediment must be removed for the system to continue to work properly. The presence of elevated concentrations of heavy metals indicates that proper handling of sediment is necessary to insure sound remediation. In addition, primary producers may take in heavy metals from sediments, resulting in reduced vitality and subsequent bioaccumulation. Determining the mineral phases in which the heavy metals are concentrated is crucial in order to assess the potential for bioaccumulation and other potential consequences of heavy metal accumulation.