The Marysville Downtown Stormwater Treatment facility treats 463 acres of urban runoff, meeting Washington State Department of Ecology enhanced standards for regional treatment of existing and new development. The facility supports Marysville’s long-term vision to improve the waterfront area for the community. It is integrated into the downtown waterfront park, trail system, and commercial setting which will serve as a new destination for downtown visitors.
This project is the first large-scale treatment facility to use newly approved Filterra Bioscape engineered media, which provides filtration rates of up to 175 inches per hour. This design allows the project to take up only half an acre to treat the 463-acre urban area. Typically, a project of this scale would require several acres.
The facility includes an on-site pump station, using gravity for the water to flow through pretreatment, flow control, and treatment systems prior to discharge. Four uniquely shaped treatment cells are housed within above-ground concrete structures. Each treatment unit has a different footprint and treatment media and will treat different amounts of stormwater. The hydraulic design controls flows using a series of large adjustable weirs. The first set of weirs balance the water between the treatment units. A second set of weirs evenly distribute the stormwater within each individual treatment cell. These vaults contain distribution troughs to ensure the uniform distribution of stormwater throughout the system.
The treatment facility has performed extremely well, treating large volumes of stormwater for several months, including during winter storms. The facility is accessible and a visually appealing part of the park. It provides capacity to support future economic development of the downtown and it helps to educate the public of the importance of water quality for public and ecological health. The facility will clean 110 million gallons of water every year, preventing more than 100,000 pounds of pollution from entering waterways over the next 20 years.
