ASSESSMENT OF THE EFFECTIVENESS OF A VERTICAL FLOW WETLAND PASSIVE TREATMENT SYSTEM FOR ABANDONED MINE DRAINAGE

The Shamokin Creek Watershed (Northumberland Co.) lies in the middle anthracite field in Pennsylvania. Within the Shamokin Creek Watershed lies Scarlift Site 15 where the mine drainage (about 600 gpm) before treatment has been reported to have a low pH and high concentrations of iron, aluminum, and manganese. August 2006 marked the opening of a vertical flow wetland (VFW) treatment system at the site thanks to the efforts of the Shamokin Creek Restoration Alliance, with the cooperation of state and federal agencies. A four pond treatment system was designed to reduce metal loading and raise alkalinity of the drainage before release into Shamokin Creek. Due to property limitations, the treatment system could not be built large enough to handle the full discharge. We sampled the site on 3 October 2008 with the goal of evaluating the effectiveness of the VFW system. At the time of sampling, the system was operating under minimal flow with only the first pond on-line due to excessive off-gassing of hydrogen sulfide when fully operational. We measured in-situ dissolved oxygen, pH, and temperature and collected filtered samples for laboratory analysis of alkalinity, sulfate, and various dissolved metals. Treated water from the first pond was higher in pH, Ca, and alkalinity, facilitating the precipitation of aluminum in the second pond. This water also showed lower Fe, Zn, and DO. Microscopic examination of sediments in the ponds and outflow revealed biologically precipitated iron oxyhydroxide.