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King County Washington home

SODO Wet Weather Treatment Station

Project update

July 2026

This project is currently in the design phase.

Field survey work continues

We are doing on-the-ground field surveys in the project area. This work helps us plan our design and prepare for future construction. The surveys show us what is underground near our planned facilities. They also help us identify places that may be culturally or historically important. 

This survey work began in summer 2025. We expect it to continue through summer 2026. 

If you see survey activity near North Delridge, here’s what to expect: 

  • Standard work hours are 7:30 a.m. to 5 p.m. We will reach out to nearby businesses in advance if we plan work outside these hours. 
  • Crews typically use one truck and one survey vehicle  
  • You may hear engine noise or hammering while crews are working. You may also feel slight vibrations. 
  • Crews may need to set up detours. If they do, flaggers will assist drivers and people walking or biking.  
  • Crews will remove equipment and restore disturbed surfaces once work is complete.  

Thank you for your continued coordination as our crews complete this work. 

Find more information about this upcoming work. 

Upcoming community events

Come meet our team this summer and learn more about Mouth of Duwamish Wet Weather Facilities. 

SODO Business Improvement District National Night Out

When: Tuesday, August 4, 2026, from 4 – 6 pm  

Where: Canine Companions Puget Sound Field Office - 2454 Occidental Avenue South  

What: Connect with community members, business owners, and local law enforcement over cold drinks and tasty bites. Register here.  

SOPASUPA x Duwamish River Fest x River City Skatepark

When: August 8, 2026, from 12 pm – 9 pm  

Where: 14th Avenue South and Cloverdale Street South / Duwamish River People’s Park – 8700 Dallas Street South  

What: Join your neighbors for an epic day of free music, kid’s activities, skateboarding, beer garden, cultural traditions, and more. Learn more about the event here.  

Stay informed

We will share updates as design continues.

Sign up for email and text updates for the Chelan Wet Weather Storage project.

Contact the project team

Questions or comments are always welcome. Contact Broch Bender using one of the channels below.

Map showing the planned SODO project area. The map includes a treatment station, new pipes, and other upgrades. The project helps treat polluted water before it enters the Duwamish River and Elliott Bay during storms.
Map showing the planned SODO project area. The map includes a treatment station, new pipes, and other upgrades. The project helps treat polluted water before it enters the Duwamish River and Elliott Bay during storms.

Project description

During heavy rain, extra water can overflow into the Duwamish River and Elliott Bay. We plan to build a new wet weather treatment station in SODO to help reduce these overflows. The station will remove solids and kill germs before the water is released.

The station will work in big storms, when we need it most to protect Puget Sound. The County plans to build the facility on about 8 acres of land near South Spokane Street and First Avenue South. It will have the capacity to treat up to 240 million gallons of water per day during heavy storms.

King County built another wet weather treatment station in 2022. That station is called the Georgetown Wet Weather Treatment Station. Once built, the planned SODO station will be able to treat four times more water than the one in Georgetown.

We also plan to build a new pipe to carry treated water from the future wet weather treatment station in SODO to the Duwamish River. This pipe, called an outfall, will be underwater between SODO and Harbor Island. It will not be visible from the shore.

The planned station will need to connect to existing sewer system. Connecting the station will require new pipes and support facilities. We will also need to upgrade some older facilities. These changes will make sure the station works.

We plan to build new pipes under the following roads in SODO:

  • Utah Avenue South from South Lander Street to South Hinds Street
  • South Hinds Street from Utah Avenue South to the Duwamish River
  • South Royal Brougham Way near Pioneer Square, on the shore of Elliott Bay
  • South King Street near Pioneer Square, on the shore of Elliott Bay

NEEDS ALT TEXT

The conceptual illustration shows what the SODO Wet Weather Treatment Facility could look like. The building design and site features, including the fence, is in progress and may change as work continues. The planned wet weather treatment station will be near South Spokane Street and First Avenue South in SODO.

Keeping pollution out of our waterways

  • The wet weather treatment station will treat large storm flows during heavy rain.
  • This will reduce polluted overflows into the Duwamish River and Elliott Bay.
  • It will help protect water quality and Puget Sound.

How the sewer system works

The steps below show how the sewer system works on dry days, during storms, and after the rain slows.

On dry days or during light rain

  • Local combined sewer pipes collect water from homes, businesses, and streets.
  • These pipes connect to larger pipes called trunk sewers.
  • Regulator stations control how water moves into these larger pipes. Think of them like traffic lights that help keep water flowing through the system.
  • Water then flows underground through trunk sewers to West Point Treatment Plant.
  • West Point Treatment Plant cleans the water before it enters Puget Sound.

Overflows during heavy rain storms (today)

  • Large amounts of rainwater run off streets and rooftops into storm drains. This sends much more water into the sewer system than on a typical day.
  • The combined sewer pipes in the area can fill faster than the system can send water to the treatment plant.
  • When there is too much flow, the system sends extra water to overflow pipes. These pipes are located along the Duwamish River and Elliott Bay.
  • This releases a mix of stormwater and sewage into nearby waterways. This is called a combined sewer overflow, or CSO.

Treatment and safe discharge during storms (in the future)

  • Instead of going to CSO outfalls, extra water will flow to the new SODO Wet Weather Treatment Station.
  • New pipes will help carry the extra water to the station during large storms.
  • The station will remove solids and disinfect the water to kill germs.
  • The treated water will travel through a new outfall pipe in the Duwamish River. The new outfall pipe will be underwater between SODO and Harbor Island.

Project Schedule

A dark background graphic showing three horizontal blue timeline bars. The left bar reads ‘January 2024 – May 2025,’ the center bar reads ‘May 2025 – 2029,’ and the right bar reads ‘2029 – 2034.’ The bars progress from lighter blue on the left to darker blue on the right.

Project funding

The King County Wastewater Treatment Division pays for this project. Ratepayers help fund this work through sewer charges on their local sewer bill.

The current estimated cost for this project is $2.2 billion. This estimate is subject to change.