Meghan Jacobson, Stormwater/Wastewater Education Coordinator, 509.625.7900
Friday, February 21, 2025 at 1:26 p.m.
When the City experiences significant rainfall or a quick rise in temperatures causing fast snow melt, the Combined Sewer Overflow System – referred to as the CSO system – does exactly what it was designed and built to do. It protects the Spokane River from untreated sewer and stormwater.
CSO tanks play a critical role in preventing pollution, controlling flooding, and ensuring sustainable water management practices. There are over 1,250 miles of pipes in the City’s wastewater collection system, that’s as many miles as it takes to drive to Disneyland! Most of the time the amount of wastewater that travels through them is consistent. CSO tanks address the challenge of combined sewer systems, which carry both stormwater runoff and sewage in the same pipes when rain events and fast snow melt happens.
During short and intense, or sustained heavy rain events, or when temperatures increase quickly with snow on the ground; these systems can overflow, releasing untreated wastewater into the Spokane River and other waterways. These CSO tanks prevent this by temporarily storing excess storm and wastewater until the treatment plant can process it. Essentially, they are a waiting room for dirty water before it can be processed.
Spokane’s investment in CSO tanks has significantly reduced pollution to the Spokane River, protecting aquatic ecosystems and enhancing water quality. Because of this system, over 99% of all storm and wastewater is cleaned and treated before it re-enters the Spokane River. In 2024 that was over kept 8.7 million gallons of combined sewer from spilling to the Spokane River!
Beyond pollution prevention, CSO tanks also reduce urban flooding by controlling the release of excess water, safeguarding streets and homes. Spokane’s ongoing commitment to maintaining and improving these systems ensures a sustainable future for managing wastewater and protecting our waterways.
Join us on this video tour of CSO tank number 26 (which holds 2.2 million gallons) so you can see it in action!
The next time you are enjoying the views of the Spokane Falls at the Place of Truths Plaza, watching school kids getting some outside exercise on east Sprague, or enjoying some music and a beverage at the Brickwest Plaza, stop to remember that below ground is a multi-million-gallon tank ready to protect our most precious asset, the Spokane River.
Here are some fast facts:
If you are interested in a tour, please contact our Stormwater Education Coordinator, Meghan Jacobson at mjacobson@spokanecity.org to schedule an appointment.
Learn more at SpokaneStormwater.org!
