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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

August 29, 2014 Update -

On Tuesday, September 2, King County’s contractor will begin installing shoring for a drill pit on the east side of 32nd Avenue West. This work can be noisy, and will last 3-5 days. You can expect more construction activity on the street. 

What neighbors can expect during shoring for the drill pit:
• New equipment and materials at the site.
• Increased construction traffic, including oversized loads along the project haul route (32nd to Magnolia Avenue W to Magnolia Bridge) as equipment is delivered
• Increased construction activity, noise and possible vibrations
• The contractor will be monitoring vibration levels throughout the shoring process

What is shoring?
It is a general construction term that refers to methods used to help keep excavations safe and open during underground construction and to prevent surrounding soils from running into the excavated pit. Many different shoring methods can be used depending on the type and size of excavation, surrounding soils, and water table.

Latest construction update: Construction on 32nd Ave W (PDF, August 29, 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