Last of Tanks to Manage Overflows from Combined Sewers Comes On Line

Watch the construction time-lapse video

Marlene Feist, Public Works, (509) 625-6505


Monday, September 21, 2020 at 10:52 a.m.


On Monday, officials from Garco Construction presented Spokane Mayor Nadine Woodward with a ceremonial “key” to CSO 26, a massive underground storage tank on Spokane Falls Boulevard designed to manage overflows from combined sewers to the Spokane River.

“This is the coolest project I’ve ever gotten to work on and frankly, the most important to me,” says Kyle Twohig, the City’s Engineering Services Director “Most of the combined wastewater water that previously entered the river came from this location right here. This project will improve our river now and for the future.”

Garco is the contractor on the project, which took nearly three years to complete. A time-lapse camera, perched on City Hall, recorded the project over that time. Garco contracted with a company called TrueLook to provide the time-lapse video.

The two minute recording contains more than 187,000 images and captured Spokane’s changing seasons. Click here to see the time lapse video.

“After you view the time-lapse footage, you’ll be able to develop an appreciation for the complexity of the CSO 26 project,” says Justin Ludwig, the project manager for Garco. “The time-lapse footage will also serve as a reminder for all of our employees of all the hard work we did to protect the Spokane River, as well as create this great open space for the community to use.”

The CSO 26 tank can hold 2.2 million gallons of wastewater and is now fully operational. It is part of an overall system that includes about two dozen underground tanks with a total of 16 million gallons of storage for combined wastewater and stormwater.

In some parts of the City, wastewater and stormwater sewers are linked together, and during periods of heavy rain or rapid snowmelt, these pipes can become overwhelmed and overflow to the river. Tanks store the excess water until the storm surge subsides and the water can be sent to the Riverside Park Water Reclamation Facility for treatment.

Like most CSO projects, Tank 26 provides dual benefits above and below ground. While the basin detains pollution, a new plaza on top of the tank provides visitors sweeping view of the Spokane River. The plaza opened to the public in May.

Overall, the City is investing more than $350 million to improve the health of the river. A major upgrade at the City’s treatment plant continues as well.