A GEOCHEMICAL ANALYSIS OF AN ACID MINE DRAINAGE TREATMENT SYSTEM NEAR RANSHAW (NORTHUMBERLAND COUNTY), PA

The Scarlift 15 site, near Ranshaw, PA (Northumberland County), is a vertical flow wetland treatment system designed to treat low pH and alkalinity and high sulfate and iron concentrations in mine drainage from the Corbin Mine Drift before it flows into Shamokin Creek. The system contains four treatment ponds: an oxidation pond followed by three vertical flow wetlands (VFW), each consisting of a layer of compost (for sulfate reduction) above a layer of limestone (to raise pH and alkalinity). Iron is removed by oxidation in the upper portions of the ponds. Water samples were collected at 20 sites in the Scarlift 15 system and Shamokin Creek on October 26, 2012 to assess the effectiveness of the system. In situ analyses included pH, temperature, dissolved oxygen, and conductivity. Turbidity was measured on site on non-filtered samples; alkalinity and acidity on filtered samples. Samples were preserved for later laboratory analyses for simple cations, anions, and selected heavy metals. The pH of Shamokin Creek remained relatively constant upstream and downstream of the treatment system at the sites selected. Although the pH from the outflow pipes from each vertical flow wetland was raised relative to the surface water in that wetland before treatment, net pH values declined across the downstream wetland, most likely due to the precipitation of aluminum and iron hydroxides in the ponds. Sulfate concentrations were not reduced throughout the system, and in fact were higher coming out of the outflow pipes of the second and third vertical wetlands than they were before treatment, implying the system’s compost component is no longer effective. Additional studies are needed to determine specific causes of the failure of this system regarding sulfate reduction. Both dissolved iron and aluminum are being removed from the treated water by the VFW, although the dissolved iron in the final effluent is still far above the EPA standards for drinking water. This VFW system was not designed to remove manganese, and indeed no manganese is being removed, with 3.5 ppm dissolved manganese exiting from the mine and from the treatment system.