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South Henderson Basin

52nd Ave. S. Combined Sewage Overflow (CSO) Reduction Project

Project map52nd Ave S. and Mapes Creek project map.

SPU is installing a new combined sewer line from Rainier Ave. S., up 52nd Ave. S. (the Mapes Creek Walkway) and along S. Henderson St. to the King County pump station. The new combined sewer line will reduce overflows of combined sewage into Lake Washington during heavy rain events.

It is being constructed in conjunction with the Lower Mapes Creek Restoration Project, which will move flows from Mapes Creek out of a storm drain pipe, into its own dedicated pipe and restore approximately 400 feet of creek channel within Beer Sheva Park. Learn more about the Lower Mapes Creek Restoration Project.

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Project Benefits

  • Protect public health by reducing overflows of raw sewage into Lake Washington.
  • Provide public art to the Rainier Beach community.
  • Improve landscaping within the community.

Project Impacts

  • The S. Henderson St. sidewalk between Rainier Ave. S and Seward Park Ave S. is now fully open to pedestrian traffic.
  • The Mapes Walkway remains closed until mid-August as the artist finishes the public artwork.

Project Schedule

Construction started at the beginning of 2014 and is scheduled to be complete in late September 2014. See the Lower Mapes Creek Restoration Project site for information about the schedule in Beer Sheva Park. Thank you to everyone in the community for your patience and cooperation during construction!

We are also working on a combined sewer overflow reduction project in the North Henderson basin. Please visit the North Henderson Basin website for additional details.


Contact Alan Lord, Project Manager by email or at (206) 233-1565

For interpretation services please call (206) 233-1565
Para servicios de interpretación por favor llame al (206) 233-1565
Về dịch vụ phiên dịch xin gọi (206) 233-1565
Hadii aad u baahantahay turjubaan, fadlan inaga soo wac telefoonkan (206) 233-1565
如需要口譯服務,請撥電話號碼 (206) 233-1565


South Lake Washington Sewage Overflow Reduction Project


Seattle Public Utilities (SPU) held an open house in March 2014 to present information and receive feedback on the South Lake Washington Sewage Overflow Reduction Project. SPU is planning to build additional storage for polluted stormwater and sewage to prevent future overflows into Lake Washington and comply with state and federal regulations. SPU has been considering potential options and locations for underground storage near Rainier Ave. S., between 57th Ave. S. and Lakeridge Park.

Open house materials (fact sheet and display boards) provide more background on the project and information on the options SPU has considered.

Current Status

Preferred Alternative

The project team has selected our preferred alternative for this project. The preferred alternative, known as the “East of Rainier Ave.” option, is an underground storage tank to be constructed on SPU-owned property. Additional details on this alternative are described in the updated project fact sheet.

Schedule Updates

After reviewing our sewage overflow reduction program and our regulatory requirements, SPU has decided to reschedule the completion date for this project. We now plan to initiate design in 2020, and complete construction in by the end of 2024. Delaying the project a few years provides an opportunity for SPU to field monitor two other nearby projects that will be completed in the next few years. This will help us better understand the modified volumes of stormwater and sewage flows, and determine with more accuracy the required storage needed within this basin.


Please contact Grace Manzano at or at (206) 233-1534.
For interpretation services please call (206) 233-7861
Para servicios de interpretación por favor llame al (206) 233-7861
Về dịch vụ phiên dịch xin gọi (206) 233-7861
Hadii aad u baahantahay turjubaan, fadlan inaga soo wac telefoonkan (206) 233-7861
如需要口譯服務,請撥電話號碼 (206) 233-7861