Constructed Wetlands Treatment System
Malvern, Arkansas
FTN conducted a feasibility study to determine if a constructed wetland treatment system could potentially treat the low pH, high sulfate acid mine drainage from pits at a clay mining facility in central AR. Based on a review of the wetlands treatment literature, hydrologic studies, and water quality analysis, it was determined that an anaerobic, subsurface flow, sulfate reducing wetlands could be used to increase pH, and reduce sulfate concentrations in the acid mine drainage. The development of a conceptual treatment system design and an estimate of design, construction, operation and maintenance costs for the constructed wetlands were also completed as part of this feasibility study.The design criteria for a 0.25-acre demonstration wetlands treatment system were developed based on laboratory column tests conducted by FTN. Various media, flow rates, and hydraulic residence times were studied for their effectiveness in removing sulfates and increasing pH in these column tests. FTN developed the design criteria for a 0.25-acre vertical flow, anaerobic, sulfate reducing wetlands treatment system that was then designed by B&F and was constructed by the Client. The demonstration wetland was monitored for one year and was evaluated for its performance in meeting National Pollutant Discharge Elimination System (NPDES) permit limits and operating conditions. Following the evaluation of the demonstration system, a full-scale system was designed by FTN to treat an average of 625,000 gpd of acid mine drainage. The gravity system includes retention basins, transfer piping, flow control structures, and five parallel wetland cells discharging to a common outlet structure. Construction cost for the full-scale system was approximately $950,000.
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