LONG TERM MONITORING OF PASSIVE ACID MINE DRAINAGE TREATMENT SYSTEMS IN A SMALL WESTERN PENNSYLVANIA WATERSHED

Western Pennsylvania has been extensively mined for coal and many abandoned mine locations actively discharge acid mine drainage (AMD), which impacts water quality, and macroinvertebrate richness and density in the receiving streams. The headwaters (70 km sq) of Slippery Rock Creek Watershed have been significantly impacted by AMD from numerous abandoned mine locations. AMD flow varies among sites from several liters per minute to several hundred liters per minute. While all discharges are acidic, the water chemistry also varies among sites. A water quality monitoring program consisting of twelve stations in the headwaters was established in 1995. The stations have been sampled approximately twenty times between the summer of 1995 and the spring of 2007. Two stations are unimpacted control sites. Data have been collected for flow, alkalinity, acidity, pH, sulfate, and a suite of metals (total and dissolved). In addition, epilithic and epipelic algae, and macroinvertebrates have been collected at seven of the stations. During the same period, eleven passive treatments systems for AMD have been constructed in the headwaters. The treatment systems have reduced metal and acid loading to the streams, but improvement in the overall stream water quality, while occurring, has been slower than originally anticipated. Sulfate levels have remained elevated indicating AMD still is discharged to the watershed; increasing alkalinity levels demonstrate the positive impact of the passive treatment systems. However, the chemical factors that are limiting the recovery of the biota remain elusive. The study area is located within five miles of the University and has involved a significant number of undergraduate students. Data have also supported the efforts of a local watershed group who has been the driving force in the construction of the treatment systems.