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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

South Magnolia CSO Control Project

Project Construction

September 12, 2014 Update -

King County’s contractor is continuing work on 32nd Avenue West to prepare to install the new gravity sewer pipeline. Shoring of the drill pit on the east side of the street is nearly complete.

Next week, September 15-19, crews will set up heavy drilling equipment and conduct surveying work on 32nd Avenue West. During this work, expect increased activity on the street and construction noise. Work hours will be Monday through Friday, 7 a.m. to 7 p.m.; Saturdays, 9 a.m. to 5 p.m. Flaggers will direct traffic through work zone.

Neighbors will hear noise from drill pit preparation work, and may feel some vibration near the site. The contractor will be monitoring vibration levels.  People are more sensitive to vibration than structures, and while you may feel vibration, it does not mean that problems will occur as a result.

Work is also continuing at the CSO storage facility site on 23rd Avenue West in the Smith Cove area.

Latest construction update: Construction on 32nd Ave W (PDF, September 12, 2014)

Project area for the South Magnolia CSO control project elements (diversion structure, gravity sewer, storage tank)
South Magnolia CSO basin project area
How will the new CSO facility work? View animation.

Project vicinity map
South Magnolia basin and project location.

Project description

King County is building a new gravity sewer pipeline and an underground storage tank in Magnolia. This facility will store peak combined sewer flows so that discharges of untreated wastewater and stormwater are limited to no more than one per year on a long-term average.

Why does King County need to do this project?

This project is included in a federal consent decree that requires completion by December 2015.

Project schedule

2014-2015 activities

Activities Dates
Pre-construction community meeting - storage January 30, 2014
Pre-construction community meetings - conveyance May 13 & 14, 2014
Construction 2013 - 2015

South Magnolia CSO Control Project Timeline, May 2013
View meeting calendar for upcoming public meetings, and South Magnolia CSO Control Project Timeline (PDF), updated May 2013.

Hotline - South Magnolia CSO Control Project
24/7 Construction Hotline: 206-205-0968
Leave a message, and a project team member will return your call.
Project contact: Monica Van der Vieren, 206-477-5502, or via feedback form.

Project updates

News releases

Related information