The A-01 NPDES outfall at the Savannah River Site receives process wastewater discharges and stormwater runoff from the Savannah River Technology Center. Routine monitoring indicated that Cu~(++) concentrations were regularly higher than discharge permit limit, necessitating treatment of nearly one million gallons of water each day plus storm runoff to meet compliance standards. A conceptual design for a constructed treatment wetland was developed as the most cost-effective alternative. A pilot study was conducted using mesocosms to confirm that the design concept would reduce Cu~(++) to acceptable levels. After treatment in the mesocosms, effluent Cu~(++) concentrations were routinely below permit limits, even though the influent concentrations varied widely. During the research phase the wetland system was also effective at reducing total and dissolved Hg~(++). Constructed in the summer of 2000, the treatment system consists of four pairs of one-acre (0.4 hectares) wetland cells (eight acres (3.24 hectares) total) with water flowing from one cell to a second cell, then to the discharge point. The cells are vegetated with Scirpus californicus, and water retention time in the system is approximately 48 hours. Results of the full-scale system during the operation start-up phase have mimicked those generated by the mesocosm study. Cu~(++) concentrations at the effluent discharge are often below detection limits (10 μg/L), and total Hg~(++) concentrations are reduced throughout the water path through the wetland system. Cu~(++) removal efficiency was excellent from the start-up of the system, while Hg~(++) efficiency has improved with maturation of the treatment cells. Vegetation development within the cells has been excellent, surpassing 2.5 kg/sq. meter of dry above-ground biomass. Operation and maintenance of the system is minimal, and mainly consists of checking for growth of the vegetation and free flow of the water through the system. This has provided a low cost construction option and low cost maintenance program for the effective treatment of large volumes of permitted water discharges from an industrial area.
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