Facility Alternatives
In December 2004, the County Executive selected a property within city limits at the west end of Entwistle Street for the new wastewater treatment plant and eliminated further consideration of the upland discharge alternative. Both the wetlands enhancement and river discharge alternatives were carrried forward for continued evaluation. For more information, see why were the treatment plant site and disharge alternatives chosen?
To view proposed alternatives evaluated by the Final Environmental Impact Statement, click here. Selected Wastewater Treatment Facility
Description
In the United States, most treatment plants treat wastewater to the secondary level, a level of treatment required under the federal Clean Water Act and other laws.
The Carnation wastewater treatment plant will exceed those standards by using an advanced treatment process called a membrane bioreactor.
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Selected Carnation Wastewater Treatment Facility with Revised Wetlands Option (January 2007). Click image for larger view.
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River downspout design. Click image for larger view. |
The Carnation wastewater treatment system will be composed of a treatment plant, conveyance pipeline and discharge location. The plant will initially have the capacity to treat up to 400,000 gallons of wastewater per day. The capacity could be expanded to treat about 450,000 gallons per day to meet planned growth. Proposed construction of the facility began mid-2006. The plant is expected to begin startup operations in late 2007.
The Treatment Plant
The treatment plant will be on city-owned property within city limits at the west end of Entwistle Street. The treatment plant will occupy about two acres of the 10-acre city-owned site. The city also plans to build its wastewater pump station just south of the treatment plant on the city-owned site. Information on the vacuum system can be found on the City of Carnation's web site at http://www.ci.carnation.wa.us/
sewer/factsheet-vacsystem.pdf
The conveyance route will go from the treatment plant to a river discharge near the northwest end of Carnation Farm Road Bridge .
First Phase—River Discharge
Highly treated effluent from the plant will be discharged to the Snoqualmie River at the Carnation Farm Road Bridge about a mile north of Carnation. The effluent would be discharged through a diffuser at the end of the 8-inch pipe that would extend from the northeast side of the Carnation Farm Road Bridge to the northwest bridge support pier. The river outfall will discharge highly treated effluent to the river via a downspout mounted on the bridge. This innovative design will minimize disturbance to the river bottom during both construction and operations.
Second Phase—Wetlands Enhancement Discharge
As soon as the treatment plant successfully comes online and passes all water quality treatment tests, reclaimed water will be used to enhance a wetland at Chinook Bend Natural Area. Reclaimed water will be used to enhance the natural area and provide habitat for native plants, aquatic life, birds and wildlife. This project will consist of introducing reclaimed water to existing low areas in the former trickling water into the existing farm pond on site. The goal is to eventually have the wetland enhancement as the primary discharge option with the river discharge functioning as a backup.
For more information
See why were the treatment plant site and disharge alternatives chosen?
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