INVESTIGATION OF TRACE METAL TRANSPORT IN AN AMD-IMPACTED STREAM AND TREATMENT SYSTEM IN NORTHEASTERN OHIO

Acid mine drainage (AMD) results when pyrite-rich coal oxidizes to release high concentrations of sulfate, metals, and acidity that can destroy aquatic ecosystems and poses serious health threats to human populations utilizing contaminated water bodies. Treatment of acid mine drainage often includes running contaminated water through limestone channels designed to neutralize acidity and precipitate iron oxides and other metals. A limestone channel was recently installed in HR25, a subwatershed of the Huff Run Watershed in northeastern Ohio, to treat acidic, metal-rich water draining from an abandoned underground coal mine into a small tributary stream. Here, we investigated the effectiveness of the treatment system by analyzing changes in water chemistry (cations, anions, DOC, electrical conductivity, DO, pH) along the length of the treatment system and in the tributary. Sampling sites included upstream of the mine pool, the mine pool, the limestone channel, two settling ponds, and the stream at the watershed outlet. Along the treatment system, pH increased from ~4 in the mine pool to ~8 in water draining the limestone channels. Concentrations of dissolved metals (Fe, Mn, Al) decreased due to extensive precipitation of oxide minerals. However, water discharging from the watershed outlet downstream of the treatment system was acidic (pH < 3) and metal-rich (4.2 mg/L Al, 15.8 mg/L Fe, and 29.8 mg/L Mn). These results indicate that, while the treatment system is effective in neutralizing acidity and removing metals (e.g., Fe) from water draining the mine pool, the system does not neutralize all of the inputs to the stream. We infer that an additional, unidentified input to the tributary decreases pH and increases metal content of the water that discharges from HR25 to the Huff Run. Future studies will explore the possibility of the mine pool draining into the stream, groundwater upwelling, surface runoff, or other possible inputs of acidity to the stream.