ANOXIC LIMESTONE DRAIN - REMEDIATION OF PINE FOREST MINE IN ST. CLAIR, PENNSYLVANIA

The abandoned coal mine, Pine Forest Mine, is located in St. Clair, Pennsylvania. Remediation at the drainage tunnel from the site was needed to improve the low pH and low alkalinity and to reduce high amounts of dissolved iron and other metals released to Little Wolfe Creek. An anoxic limestone drain (ALD) was installed in the fall of 2007 as a remediation strategy to improve the water quality. The anoxic limestone drain consists of two underground channels covered with limestone, each with two exit drains at the surface water, and four consecutive settling ponds. On April 11, 2015, water samples were taken above the system, below the system, and at each settling pond to determine if the system is working as designed.

At the time of sampling, the system was functioning as designed. The pH was raised to almost 7. Alkalinity, which was 47.7 mg/L as Ca CO₃ coming out of the mine shaft, was raised to 101.1 mg/L exiting the ALD. Concentrations of iron and aluminum were reduced by about 85%. At the time of sampling the ALD was removing 40,036,060 mg/day of iron. Manganese and sulfate were reduced by about 10%. There is upwelling above the anoxic drain site, indicating that oxygen is getting into the system before reaching the ground surface and also that all the discharge water is not going through the ALD. The discharge at the drain site was not completely anoxic, but it had oxygen levels as low as .34 mg/L. The ALD has exhibited an ongoing problem of clogging due to microbial iron precipitation in the ALD. The great amount of metals settling in the ponds is also reducing the available space in the settling ponds, reducing retention time. As a result, these ponds may soon need to be dredged of the iron precipitate in order to remain functional.