Efficiency of Passive Treatment Systems for Treating Acid Mine Drainage and Their Impact on Receiving Streams

The project area comprises the 70 km² headwater drainage basin of Slippery Rock Creek in northwestern Pennsylvania. Slippery Rock Creek and its tributaries have been adversely impacted by acid mine drainage for over a 100 years and at present, over 75 groundwater discharges from abandoned coal mines have been identified within the watershed and of these, 59 are contributing acid load to receiving streams. The pH of these streams varies from 2.5 to 6.0 with acidity exceeding alkalinity and heavy metals varying from 2 to over 100 mg/L. To date, 15 passive treatment systems are removing 30% of the acid loading and contribute 193 kg/day of alkalinity to receiving streams with the treated effluents maintaining pHs between 6.8 and 7.2. In addition, these systems are removing over 27% of the metal loading to receiving streams. Biological surveys of the Slippery Rock Creek and its major tributaries revealed that fish and macroinvertebrates are beginning to recolonize the streams below the discharges from the passive treatment systems.