Long-term performance of passive acid mine drainage treatment systems

Abstract:

State and federal reclamation programs, mining operators, and citizen-based watershed organizations have constructed hundreds of passive systems in the eastern United States were developed over the past 20 years to provide reliable, low cost, low maintenance mine water treatment in remote locations. Passive treatment methods can be grouped into about 9 categories

While performance has been reported for individual systems, there has not been a comprehensive evaluation of the performance of each treatment type fo r a wide variety of conditions. We evaluated 83 systems comprised of five system types in eight s tates ; this project evaluated the performance of these methods by studying 137 treatment units in eight eastern States. . Each system was monitored for influent and effluent flow, pH, net acidity, and metal concentrations. Performance was normalized among types by calculating acid load reductions and removals, and also by converting construction cost, projected service life , and metric tonnes of acid load treated into cos and dimensioned as t per tonne of acid treated tons.

Of the 83 systems, 82 reduced acid load. Average acid load reductions were 9.9 t/yr for open limestone channels (OLC), 10.1 t/yr for vertical flow wetlands (VFW), 11.9 t/yr for anaerobic wetlands (AnW), 16.6 t/yr for limestone leach beds (LSB), and 22.2 t/yr for anoxic limestone drains (ALD).

Average costs for acid removal varied from $83/t/yr for ALDs to $527 for In addition to evaluating the performance of the treatment methods, this paper describes the various passive treatment systems, their applications and performance data for individual treatment units. AnWs. Average acid removals were 25 g/m 2/day for AnWs, 62 g/m 2/day for VFWs, 22 g/day/t for OLCs, 28 g/day/t for LSBs, and 56 g/day/t for ALDs. While it appears that the majority of passive systems are effective, there was wide variation within each system type, so improved reliability and efficiency are needed.

This report is an initial step in determining passive treatment system performance; a . Additional work is needed to refine passive system designs and monitoring.