THE PINE FOREST ACID MINE DRAINAGE TREATMENT SYSTEM, ST. CLAIR, SCHUYLKILL COUNTY, PA: AN ANOXIC LIMESTONE DRAIN WITH AN OXYGEN PROBLEM

At the request of the Schuylkill Conservation District, we designed a sampling scheme to assess the effectiveness of the Pine Forest AMD Passive Treatment System, an anoxic limestone drain (ALD) in St. Clair, PA. Drainage from the Pine Forest Mine flows directly into an ALD to raise the alkalinity, then flows into a series of large settling ponds. Key to successful operation of ALD’s is the exclusion of oxygen so that dissolved iron stays in solution and does not precipitate out and armor the limestone.

Conductivity, pH, DO (% saturation), temperature, were measured in situ at 9 sites in the system. Large volume samples (4 L) were collected at each site, and analyses for alkalinity and acidity were executed on site in triplicate. Triplicate samples of both filtered and unfiltered water from each site were acidified, chilled and transported to the lab for later analysis of selected metals. An additional set of triplicate non-acidified, filtered samples from each site was collected, chilled, then frozen immediately upon returning from the field, and thawed just before analysis of selected anions. Rocks coated with iron precipitate as well as iron floc were collected at each site for later inspection with an SEM/EDS. After we sampled at sites throughout the system, the drain was flushed and we performed the same analyses on the effluent. Settling ponds were covered in iron precipitate, with abundant cattails growing in the lower two shallow ponds. The DO leaving the ALD was higher than that coming out of the mine, indicating leakage of oxygen and a not so anoxic ALD. Large amounts of what appeared to be Gallionella were in the effluent, indicating the microbe has overtaken the ALD and surrounding lithology.

The system became operational in Fall 2007, and at that time was estimated to function for 20 years requiring flushing only every few months. Instead, the Pine Forest Treatment System requires weekly flushing to remove the iron precipitate from the ALD, and the originally eight foot deep first pond is now, after only 3 years, 75% full. The chemistry indicates that the system is performing as designed (raising alkalinity and reducing iron load and acidity) but at the expense of drastically increased maintenance.