Construction and Startup of Treatment Wetlands on a Sloping Site
Abstract:When the Clayton County Water Authority (CCWA) expanded its Shoal Creek Wastewater Reclamation Facility (WRF), the effluent disposal capacity was insufficient at the existing Shoal Creek Land Application System (LAS) site to accommodate the increased capacity. Due to their interest in continuing to use natural treatment systems, CH2M HILL and CCWA worked together to design engineered wetlands that would provide the additional effluent disposal capacity required by the expansion in a configuration that would work with the existing topography. The treatment wetlands will enhance the water quality of the effluent by adding a polishing step (tertiary process) to the end of the mechanical treatment process found at the Shoal Creek WRF. The use of engineered wetlands has evolved from a research concept to an accepted and effective water treatment technology by decreasing biochemical oxygen demand (BOD) concentrations, total suspended solids (TSS), nutrients, metals, pathogens, and trace organics.
Effluent is pumped from the upgraded Shoal Creek WRF through a 1.7-mile long 24-inch transmission pipeline that enters a distribution structure where flow is distributed to 22 terraced cells through three separate flow paths. With site elevations ranging from 885 to 770 feet, and site slopes ranging from 2 to 25 percent, the site topography was a challenge. The wetland cell configuration uses the site's natural sloping topography to allow gravity flow of water from cell to cell down to a pump station where the treated water is conveyed approximately 3.2 miles to the Shoal Creek Reservoir. The treated water passes through an aeration structure before traveling into the reservoir. Since the approximately 55 acres of constructed wetland cells also captures precipitation, the pump station was sized to pump up to 11.3 mgd, which will handle a 100-year, 24-hour stormwater event. The additional captured precipitation will help maintain water levels at the reservoir. Flow from the Shoal Creek Reservoir empties into the J.W. Smith Reservoir where an intake is located for a CCWA potable water production plant. Construction was finished in June 2003. Planting began in the first “northern” completed flow path in May 2003.
The newly named Inman Road Treatment Wetland Site includes approximately 360 acres and is located south of the Shoal Creek LAS, adjacent to the Flint River on the west. This site is heavily forested with mixed pines and hardwoods in upland hilly areas, and bears hardwood bottomland forest species in the floodplain of the Flint River. The topography found onsite made it impossible to construct large, continuous wetland cells as seen in many parts of the country. Therefore, a terraced multi-cell configuration was designed and constructed at the site, which required excavation of approximately 550,000 cubic yards of earth material to construct the wetland cells. Based on the magnitude of earthwork required, challenges associated with surveying, construction phasing, and earth-moving operations were encountered during the construction process.
The total project cost was approximately 6,000,000, which included the construction of the wetlands, transmission pipelines, pump station, and outfall structure. The cost of the wetland construction only was approximately 4,000,000.
Document Type: Research Article
Publication date: 2003-01-01
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