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