Jeff Humphrey

Tanks Ready to Prevent Pollution

Jeff Humphrey, Media Manager, 509.625.6308

Wednesday, September 2, 2020 at 1:48 p.m.

The Spokane River defines our city and, with improved access, more and more of us are looking to the river for fun and serenity.

That’s one reason why, three years ago, construction started on CSO 26; a massive tank designed to protect our river and its wildlife from pollution.

“This is the coolest project I’ve ever gotten to work on and frankly, the most important to me. Most of the storm water that previously entered the river, or combined sewage and storm water, came out of this basin right here,” said Kyle Twohig, Director, City of Spokane Engineering Services.

In downtown Spokane, sidewalks, streets and buildings funnel whatever falls from the sky into storms drains.  But sometimes, heavy rains or rapidly melting snow overwhelmed our wastewater pipelines.

“In a major storm event, this one line could contribute up to 40 percent of the entire amount of flow that would overflow into the river,” lamented Twohig.

As part of the Spokane’s “Cleaner River, Faster” initiative, the City started building 26 underground tanks to hold storm-related surges until the combined wastewater could be treated.

“Think, like detention in school. It comes here temporarily, but it gets to leave eventually. And we pipe it back into the system where it winds its way down to our treatment plant, that is also currently seeing state of the art upgrades,” explained Twohig.

But it wasn’t until late August that CSO 26 went fully operational.

That’s when Garco Construction connected the new holding tank with a 60 - inch sewer line that runs underneath Lincoln Street.

“Below my feet right now, I’m standing over the main line. In the event of a big storm this flow right here will actually divert, just to the west of me, and it will go into the 2.2 million gallon tank that we just constructed,” said City of Spokane engineer Mark Serbousek from an underground vault near the Downtown Library.

CSO 26 is designed to allow maintenance crews to flush the tank with water to keep storage chambers clean and fresh when not being used.

“It was the hardest one to build, it’s the heaviest one in the system. It’s the last one to come on line right now, and it is really a special event that’s going to have a huge impact on the health of the Spokane River,” Twohig predicted.

Like a lot of our new CSO tanks, CSO 26 serves a dual purpose; pollution controls underground, but the project also created an above ground plaza. A place where the community and visitors can enjoy sweeping views of the falls as they flow through downtown.

To make it safer for people to visit the plaza and learn about the history of the gorge, as well as the program to improve the health of the river, the City is installing a raised pedestrian crosswalk in the form of a gentle speed hump.

Construction of the hump will require a closure of Spokane Falls Boulevard from the evening September 11 until 5 a.m. Monday morning September 14. Look for detours in the area.

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