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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

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Staff Contacts

South Magnolia CSO Control Project

Project Construction

July 21, 2014 Update

King County’s contractor is working overnight on the on-ramp from the Smith Cove/Elliott Bay Marina area to the Magnolia Bridge.
Drivers wishing to use the on-ramp will be detoured to and from 23rd Ave W to the off-ramp during the closure of the on-ramp. Flaggers will direct traffic coming from 23rd Avenue West across the Magnolia Bridge to continue east to 15th Ave W.

Installation of monitoring equipment beginning July 15, 2014.
View project update (PDF, July 10, 2014).

Overnight work in the Magnolia Bridge/Smith Cove area
Alternating ramp closures beginning July 7, and may extend to the week of July 21.
Alternating ramp closures beginning July 7
View project update (PDF, July 11, 2014) and news release (July 2, 2014).

Construction highlights for the storage facility and 32nd Avenue West
• Excavation for the 1.5 million gallon storage tank is underway on the County’s site in the Smith Cove/Terminal 91 area. Shoring activities should begin late June/early July.
• Utility service work for storage project is almost complete and includes power line hook ups, water sewer and storm drain services to the site
• The contractor that will build the gravity sewer pipeline is moving into the temporary construction easement on Smith Cove Athletic Field
• Preparations on 32nd Ave. W. will begin the week of June 23, 2014. Early activities will be to remove trees and brush in areas that will be used for drill rig pits and temporary roadways. Crews will also confirm locations of underground utilities using vactor trucks. View project update (PDF, June 18, 2014).
• Crews will soon begin installing monitoring points along the gravity sewer pipeline alignment; one of these locations will be in Magnolia Boulevard Park. We will provide advance notice of these activities as more detail is known.

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