Constructed wetlands are often a preferred alternative to conventional methods of treating acid drainage at mine sites, coal preparation facilities, and coal-fired power plants. The Tennessee Valley Authority (TVA) has designed and constructed wetlands in Alabama and Tennessee to treat acid discharges from these sources. Between June 1985 and August 1987, seven wetlands were constructed to treat acid drainage at an inactive coal preparation plant and adjacent mined area and four wetlands were constructed at TVA coal-fired power plants. Although sitespecific characteristics often restricted use of standardized methods, generic design, construction. and operation guidelines have been developed. Treatment efficiencies have ranged from 82%-99% removal for total iron and 9%-98% removal for total manganese. Preliminary design guidelines for required treatment area were: ph <

Many wetlands for acid drainage treatment have been constructed by the coal and utility industries with limited information on design and operating criteria. To investigate i~portant ?omponents (substrates,• vegetation. microbes) 1n wetlands treatment systems, the Tennessee Vall.ey Authority (TVA) initiated experiments at the Acid Drainage Wetlands Research Facility, Jackson county. Alabama, in September 1986. All substrates (6) provided significant treatme~t of dissolved iron. suspended solids, and pH. Acid wetland soil was initially more efficient but differences between substrates became insignificant by fall. Only limited manganese removal occurred. The pronounced pattern of removal efficiency improvement. common to all substrate types. suggested that the plant-soilmicrobial complex important to acid drainage treatment developed within all tested substrates within one year. Treatment differences between substrates were inadequate to justify added costs of deliberately installing a specific substrate in operating systems: slightly better performance of acid wetland soil supported protecting existing wetlands at construction sites.

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