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Delridge Basin

  • Anticipated future look of the Delridge Natural Drainage Systems. June 2012 - Ballard Natural Drainage System Project.
  • Anticipated future look of the Delridge Natural Drainage Systems. November 2011 - Ballard Natural Drainage System Project.
  • Anticipated future look of the Delridge Natural Drainage Systems. December 2010 - Ballard Natural Drainage System Project.

Natural drainage prevents polluted runoff from harming the fish and other wildlife that call Longfellow Creek home.


Seattle Public Utilities (SPU) is responsible for managing stormwater throughout the city. We use a three-pronged approach to prevent sewage overflows:

  • Fix It First—retrofit existing storage tanks to control up to 100 percent of the total volume.
  • Keep the Stormwater Out—add Green Stormwater Infrastructure (GSI), such as natural drainage, to protect Longfellow Creek from polluted runoff.
  • Store What’s Left—if the retrofit and GSI projects are as successful as expected, a new storage tank would not be needed.

We are currently working on two projects in the Delridge neighborhood.

Delridge Natural Drainage System Project

SPU is planning to construct a natural drainage systems project along several blocks of 17th Ave SW (pdf) in the South Delridge neighborhood. These natural drainage systems will be located within the existing planting strips and along the Seattle Department of Transportation (SDOT) proposed neighborhood greenway. By co-locating natural drainage systems projects along neighborhood greenways, the City is creating streets that manage stormwater well and provide safe and comfortable features for people of varying ages and abilities to walk, ride bikes, and get around more safely.

The project is currently in design with construction anticipated for mid-2015. View project updates

Environmental Analysis Documents

The Washington State Environmental Policy Act (SEPA) Checklist and Determination of Non-Significance were issued on October 23, 2014. The environmental impacts of the proposed Delridge Natural Drainage Systems project have been analyzed and SPU has issued a Determination of Non-Significance:

Delridge Basin Sewer System Improvement Project

We will replace the existing control systems at two existing storage tanks in the Delridge area. The tanks — one at the corner of Delridge and Orchard (CSO 2 fact sheet (pdf)) and the other at the corner of 22nd and Henderson (CSO 3 fact sheet (pdf)) — were built in the 1980s and do not operate as designed. Fixing these facilities will:

  • improve the ability to monitor and control the amount of flow allowed into the sewer system
  • reduce the frequency and volumes of sewage overflows into Longfellow Creek
  • reduce maintenance costs

Construction Updates

April 14

Seattle Public Utilities (SPU) crews are on-schedule to complete project work by October 2015. Regular work hours are Monday through Friday, 7 a.m. to 5 p.m. and Saturdays, 9 a.m. to 5 p.m. Extended work hours may be required at times. We will notify affected residents ahead of schedule changes.

Upcoming work on CSO includes the following activities:

  • Lane restrictions on SW Orchard Street will remain in place while crews begin pouring and forming new sidewalk along the street.

Upcoming work on CSO 3 will include the following activities:

  • As early as next week, crews will begin demolition work at the CSO 3 site. Flaggers will be present at the corner of SW Henderson St. and 22nd Avenue SW to help direct traffic and construction vehicles, as needed.
  • Residents may experience typical construction noise during work hours throughout the duration of the project.
  • Landscaping improvements to allow for improved sight lines around the facility.
  • Building a new access road from SW Barton Place to the new diversion structure site behind the Village West Apartments building.

Additionally, SPU will be speaking about the project at the Westwood/Roxhill/Arbor Heights Community Council meeting on May 5, from 6:15-7:45 p.m., at the Southwest Library (9010 35th Ave SW).

February 27, 2015

Work began in early February and is anticipated to be complete in September. The majority of the traffic impacts will occur in the coming two months. Our on-site crews are monitoring traffic in the area, especially during start and end times for Sanislo Elementary. We will also be installing an electronic reader board sign near Dumar Way SW and SW Austin Street to alert drivers to the construction ahead.

Please see our updated traffic advisory for anticipated construction-related traffic impacts.

February 19, 2015

Construction is now underway at both storage tanks for the Delridge Sewer System Improvement project. Most work will be on SPU property, although some work will occur in the right-of-way. During construction, residents may experience minor traffic disruptions and construction noise during regular work hours of Monday – Friday, 8:00 am – 5:00 pm.

Please see the traffic advisory for work that is currently underway at the intersection of Delridge Way SW and SW Orchard Street.

January 5, 2015

Construction for the Delridge Basin Sewer System Improvement project will begin soon. Please join us at two informal drop-in sessions to find out what to expect during construction, learn more about the planned improvements, and chat one-on-one with the project team.

Saturday, January 31
10:30 am – 12;00 pm
Intersection of Delridge Way SW and SW Orchard St.

Saturday, January 31
1:00 pm – 2:30 pm
Intersection of SW Barton Place and SW Henderson St

Sewer System Improvement Project Schedule

Pre-construction planning is happening now through January 2015, with construction anticipated to begin February 2015. Construction will take approximately seven months to complete.

Environmental Analysis Documents

The Washington State Environmental Policy Act (SEPA) Checklist and Determination of Non-Significance were published on September 16, 2013. These documents detail the regulatory compliance efforts for the retrofit project.

Connect With Us

To receive regular project updates, or for more information, please contact:

Tara Wong-Esteban, Project Manager
(206) 684-5903