DESIGN AND CONSTRUCTION OF TREATMENT WETLANDS ON A SLOPING SITE

Clayton County Water Authority (CCWA), Clayton County, Georgia, is currently upgrading the Shoal Creek Water Reclamation Facility (WRF) from its existing capacity of 1.2 million gallons per day (mgd) to 4.4 mgd. As part of the upgrade, existing effluent treatment capacity will be expanded with construction of surface flow treatment wetlands at the Inman Road site and pumped discharge to the upstream portion of the Shoal Creek Reservoir. The treatment wetlands will provide additional polishing of the pretreated effluent from the Shoal Creek WRF to a tertiary level prior to surface discharge.Constructed treatment wetlands are effective in providing advanced polishing of municipal effluents and in protecting downstream surface water resources. CCWA's use of natural wetland treatment system technologies will work well in combination with its existing land application systems (LAS). To construct treatment wetlands for additional effluent management capacity, CCWA acquired the 360-acre Inman Road site, which is located south of the Shoal Creek Land Application System (LAS) site. This site is heavily forested with mixed pines and hardwoods in upland hilly areas and hardwood bottomland forest species growing in the floodplain of the Flint River. There are approximately 225 acres of uplands. Elevations range from 880 to 780 feet in the wetland construction area.The onsite topography makes it impossible to construct large, continuous wetland cells. Therefore, a terraced multi-cell configuration was designed, with construction requiring a large volume of soil to be excavated and leveled. Approximately 550,000 cubic yards of earth material will be moved to construct the wetland cells. The layout allows for 3 different flow paths through the terraced cells. The layout uses the natural sloping topography of the site to allow gravity flow of water from the wetland cells down to a collection point where a pump station will be constructed to discharge the treated water to the Shoal Creek Reservoir. Flow from the Shoal Creek Reservoir empties into the J.W. Smith Reservoir where an intake is located for a CCWA potable water plant.Design Development Documents for construction of the wetlands were completed in April 2001. Construction bids from 4 potential contractors ranged from 4.92 to 5.44 million. The engineer construction estimate was 5.49 million. Construction is expected to begin in the fall of 2001.