EFFECTIVE PASSIVE TREATMENT OF CONTAMINATED COAL MINE DRAINAGE

Contaminated mine drainage on abandoned coal mine sites can be treated by passive or active treatment techniques. Passive treatment is less costly than active treatment, but its reliability is sometimes questioned. This paper presents a simple design approach that has been used to design passive treatment systems in Pennsylvania for the past 20 years. Five technologies are utilized: ponds, wetlands, anoxic limestone beds, oxic limestone beds, and vertical flow ponds. Technology choices are made based on mine water chemistry. A chemical flow chart is used to select appropriate technologies. The chart distinguishes first between acid or alkaline water chemistry and second according to the metal contaminants. Four systems that range in age from 3 to 18 years are presented that utilize the five passive technologies. The Marchand system uses ponds and wetlands to treat a 1,850 gpm discharge contaminated 72 mg/L Fe. The SR-114D anoxic limestone bed treats a 125 gpm flow of acidic water contaminated with 35 mg/L Fe. The Anna S passive system uses vertical flow ponds and wetlands to treat three discharges that have a total flow of 512 gpm and contain 7-34 mg/L Fe, 12-33 mg/L Al, and 7-8 mg/L Mn. The Scootac system uses an oxic limestone bed and pond to treat 50 gpm of acidic water containing 11 mg/L Al and 25 mg/L Mn. In each case the technologies consistently provide a final discharge that supports aquatic life in the receiving stream. The data demonstrate that properly designed, constructed, and maintained passive treatment systems are a highly cost-effective solution for contaminated mine discharges.