AMD Passive Wetland Treatment System

AMD Passive Wetland Treatment System Overview


GAI designed, permitted, and prepared construction plans for the collection and passive treatment of acid mine drainage (AMD) surface seepage from nine hillside seeps. The seepage was emanating from two abandoned mines located on property owned by a power station client in Pennsylvania. The purpose was to clean up AMD seepage that was mixing with stormwater runoff and discharging at existing station NPDES stormwater points. GAI’s design treated acidic, metal-contaminated water up to a flowrate of 40 gpm and pH ranging from 3.2 to 3.5. The passive treatment system consisted of a 0.31-acre vertical flow pond (clay lined/limestone underdrain anaerobic organic substrate) to neutralize pH, and a 0.34-acre constructed wetland (clay lined/emergent wetland plants) to remove residual iron and dissolved organic compounds carried over from the vertical flow pond.

The successful system was constructed in 2000. Associated work included construction specifications and an operation and maintenance (O&M) manual for long-term maintenance of the treatment system. In 2009 and 2021, GAI refurbished the vertical flow pond with new limestone and organic substrate. In 2021, GAI evaluated the constructed wetland component of the system and made O&M recommendations.

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