skip to main content

Wastewater Treatment

King County, Washington

For questions about the Wastewater Treatment Division website, please send an e-mail message or contact us at:

King Street Center
201 S. Jackson St., Suite 500
Seattle, WA 98104-3855
Phone: 206-477-5371
Fax: 206-684-1741
Telecommunication device for the deaf (TTY): 711

Get Directions to our office location in Seattle, Washington.

Staff Contacts

West Duwamish CSO Control Project

Controlling combined sewer overflows at West Michigan and Terminal 115 

Project planning

King County is working closely with Seattle Public Utilities to coordinate our projects and complement our community engagement efforts. To learn more about Seattle Public Utilities drainage projects in South Park, visit:
http://www.seattle.gov/util/environmentconservation/projects/southparkdrainage/

August 2016 Update

Thank you to everyone who joined us at Cine en el Parque and Duwamish River Festival this summer. For more information please read our newsletter (pdf) and visit the library for project updates.

project-staff-cine-en-el-parqueproject-staff-duwamish-river-festival
Project staff at Cine en el Parque (left) and Duwamish River Festival (right)

Be RainWise! RainWise, the rebate program that pays property owners to install rain gardens and cisterns on private property, has been available in South Park and Highland Park since 2013. It is available to eligible property owners through 2016.

Quick links

Project need

Like many cities around the country, the older parts of King County’s sewer system use the same pipes to carry both sewage and stormwater to a treatment plant. During storms, the pipes can fill with storm water that runs off roofs, driveways and streets. When the system is overwhelmed, it is designed to over flow to rivers, lakes and Puget Sound. These overflows are called Combined Sewer Overflows, or CSOs. Even though CSOs help prevent back-ups into homes and businesses, they pose a risk to public health and the environment.

Project description

In 2013 we brought the RainWise program to your neighborhood. RainWise rebates property owners to install raingardens and cisterns on their property, allowing storm water to soak into the ground instead of going down storm drains and into the sewer pipes. But it is not enough to reduce CSOs. This project is exploring the best way to reduce these overflows to meet federal requirements of no more than one overflow per year. Read more about RainWise and how your neighbors have been helping reduce CSOs since 2013.  

Project schedule

Project planning will continue through the end of 2016. The exact schedule will depend on which solution is identified as the best option. At this time, we expect project design to begin in 2017, and construction to begin in 2019.

Choosing the right solution for the right place

King County is working with a technical team to explore several strategies for reducing CSOs at the Terminal 115 and West Michigan outfalls. Every neighborhood and drainage basin is unique, so it’s important for the team to select the right solution for South Park. We know there is a high water table in South Park and redevelopment over the years has changed the way water flows in the neighborhood. Considerations must include:

  • Technical needs
  • Operation and maintenance requirements
  • Land use and permitting
  • Community impacts
  • Cost

We are studying three methods, or some combination of the three, to help solve the problem.

Soak it in!

gsi-solution

Using plants, trees and soil to soak up water is called green stormwater infrastructure (GSI). GSI techniques could include roadside rain gardens or permeable pavement that allows stormwater to soak through to the ground below.

Store it

store-it-solution 

Traditional infrastructure solutions use pipes and underground storage tanks to store wastewater. Tanks and pipes hold extra sewage and stormwater until there is room in the pipes again. If a storage pipe or tank is selected, that project could take place outside of South Park.

Put it in different pipes

different-pipes-solution 

A separated stormwater system consisting of two pipes: one that carries stormwater and one that carries sewage from homes and businesses. If a separated system is selected, it would include the design and installation of new pipes underground.

Working with the community

This project will protect the investments being made to clean up the Duwamish River and it will continue creating a better, cleaner river for South Park, and the region to enjoy.

work-with-community1work-with-community2

King County works with communities to provide project information, identify potential impacts, and involve the community in project design where possible. Community members can expect:

  • One on one outreach to directly impacted neighbors
  • Neighborhood meetings
  • Community group briefings 
  • Project newsletters and fliers
  • Project web page updates
  • News releases

RainWise!

During early outreach about this project, we learned that many South Park residents are excited about raingardens and other “green” solutions to keep polluted runoff or storm water out of the Duwamish. The RainWise program provides rebates that cover up to 100% of the cost of installing rain gardens and cisterns that will help manage runoff. To hear more stories about community members please view our newsletter (pdf).

If you want help getting started, call Environmental Coalition of South Seattle (external link) at 206-767-0432.

Please contact us if you would like to be on our project email and/or mailing lists, and watch this site for updates!

Project updates

  • View project library for project updates, fact sheets and other information 
    SpanishVietnamese_90

Related information

Don't feed the Tox-ick monster!
Seven simple actions you can do to protect Puget Sound
 (PDF). 
Español (PDF)

For more information

CombinedSewer-Title_190
Why does sewage overflow on the rainiest days?