Seattle Public Utilities Ray Hoffman, Director

North Henderson

  • North Henderson Project Site Aerial photo of North Henderson Combined Sewer Overflow Reduction project site in April 2016.
  • North Henderson Basin North Henderson project area.

What & Why?

What's happening now?

Construction will be underway on the Seward Park site between early 2015 and mid 2017. The park remains open, but parking will be affected. View parking map (pdf).

July 11

Construction activities at the Seward Park site:

Last week, the project reached a milestone. While there are still smaller components left to be cast for the structures (lift slabs and curbs for access hatches), the contractor completed the concrete placement for the floors, walls, and cover for both the storage tank and facility vault. With the structures mostly constructed, the contractor is moving into activities such as shoreline enhancement work and mechanical/electrical work.

The shoreline enhancement work will start in mid-July and is estimated to be complete by the end of November 2016. Work will entail grading activities, importing/exporting of material, and retaining wall construction. Work will also include adding native plants and materials to improve aquatic habitat, including for juvenile Chinook salmon. In the area south of the tank, the contractor will be moving the construction fence to the property line in order to accommodate the restoration limits of the project.

The mechanical and electrical work will start in August 2016 and should be completed in January 2017. From August to November, the contractor will perform pipe installation outside of the tanks as well as site grading. In December/January, the majority of the electrical and mechanical work will take place inside the new structures.

Your patience is appreciated. We are over halfway done with the project. Estimated completion is April 2017.

Project goals and benefits

This project will reduce the frequency of sewage overflows into Lake Washington to no more than one per year per outfall (on average). SPU plans to complete two new underground storage facilities in North Henderson to store excess combined sewage and stormwater during major rain. The underground storage facilities are in the following locations:


Ask Us

Alan Lord, PE, Project Manager
(206) 233-1565

Please specify the project site with your comments:

  • Seward Park (Basin 44) or
  • 57th Ave. S. right-of-way (Basin 45)

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