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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

Some recently completed projects

Project description Date completed
Barton Street Pump Station upgrade - This project increased station pumping capacity from 22 million gallons per day (mgd) to 33 mgd, replaced outdated electrical equipment, pumps and associated equipment, and constructed a new underground valve room and installed new valves on the force.   Fall 2015
Barton CSO Control - King County constructed 91 roadside rain gardens, a type of green stormwater infrastructure, in the Sunrise Heights and Westwood neighborhoods of West Seattle. These roadside rain gardens divert stormwater runoff away from the combined sewer system to reduce CSOs of raw sewage and untreated stormwater into Puget Sound near the recently upgraded Barton Pump Station and Fauntleroy ferry dock.   Fall 2015
West Point Treatment Plant Screenings improvement - This project addressed updated Washington State biosolids regulations to remove inert objects (trash and plastics) from solids destined for fertilizer use on farms and managed forests. King County installed new bar screens in the existing operating building and constructed a new building adjacent to the existing operating building to process the additional screened material.   Spring 2015
Interbay Pump Station - This project increased station pumping capacity, replaced aging equipment, and constructed a new generator building to provide emergency power and improve the pump station’s reliability. Winter 2015 
Kent-Auburn Conveyance System Improvements Project (Phase A) -- King County constructed two new pipelines, the Kent East Hill Diversion in Kent and the Stuck River Trunk in Auburn. These pipelines provide required capacity to accommodate recent and projected growth in Kent and Auburn. Fall 2014
Kirkland Pump Station and Sewer Upgrade Project -- This project increased station pumping capacity, replaced aging equipment, and installed a larger diameter sewer force main to accommodate increased flows. Spring 2014 
Ballard Siphon Replacement Project -- King County built a new 85-inch siphon pipe under Salmon Bay between the Ballard and Interbay areas of Seattle to accommodate growth in north Seattle and reduce combined sewer overflows into Salmon Bay. Spring 2014 
Brightwater Treatment System  -- In response to increased growth in our region, King County has built a new regional wastewater treatment system called Brightwater to serve the northern portion of the King County service area. Treatment plant operations began in September 2011. The conveyance system and outfall began full operations in fall 2012.  Fall 2012 
Bellevue Influent Trunk Improvement Project -- King County and the City of Bellevue upgraded 45-year-old sewer trunk lines along SE Third Street and 102nd Avenue SE in Bellevue to provide the required capacity to accommodate recent and projected growth in Bellevue. Fall 2012
Office Annex -- Construction was completed in August 2012 at the West Point Treatment Plant to build a permanent, modular office annex to replace temporary construction trailers. The new office space incorporates ‘green’ building materials and energy efficient design.  Summer 2012
Skyway Infiltration and Inflow Reduction Project -- This project replaced side sewers serving 332 residential properties; repaired or replaced public sewer mains and manholes; and disconnected improper storm drainage connections to the sanitary sewer. Summer 2012 
Ravenna Creek pipe extension -- This project was completed in three phases from May 2008 to September 2011. During phase A, aggressive cleanup measures were implemented after an accidental wastewater release into University Slough. Phase B consisted of extending the pipeline that conveys Ravenna Creek downstream from Ravenna Park. Phase C involved the installation of three large logs with root wads in University Slough as mitigation for the temporary rerouting of Ravenna Creek flow to the combined sewer system. Fall 2011
Bellevue Pump Station Upgrade & Force Main Installation -- This project was completed in two phases. During phase one (completed spring 2008), a new 5,300-foot-long, 24-inch-diameter pipeline was installed from the Bellevue Pump Station directly to the Eastside Interceptor, a large regional pipe near Interstate 405. During phase two, the 40-year old pump station was demolished and replaced with a facility featuring more powerful pumps, a new generator building, stronger odor control equipment and updated architecture. Winter 2011
Bothell-Woodinville Interceptor Sewer Repair -- The county repaired a severely corroded segment of the Bothell-Woodinville sewer line as part of the Hydrogen Sulfide (H2S) Corrosion Control Program. Fall 2010
53rd Avenue Pump Station Upgrade -- This Alki area pump station improvement project features new odor control equipment, upgrades to the facility's electrical and mechanical systems, and doubling the size of the below-ground facilities. Winter 2010
King Street Odor Control Facility -- This new odor control facility will reduce corrosive, odor-causing gases in the Elliott Bay Interceptor, a major wastewater conveyance pipe beneath Occidental Avenue and Second Avenue South in Seattle, and address a long-standing odor nuisance for the public. Fall 2009
Elliott West CSO Facility Emergency Repair -- The repair work is part of King County's ongoing effort to reduce CSO's into Elliott Bay. The upgrades and repairs made during this project will prevent further damage to the facility and reduce the chance of overflows into the park during storms. Fall 2009
Juanita Bay Pump Station Replacement --  This pump station replaced an older station and increases sewer system capacity while providing neighbors with a well-designed facility that can better control noise and odors. Spring 2009
Lake Hills Interceptor Sewer Repair -- The county repaired a severely corroded sewer pipeline segment along Bellevue-Redmond Road between 143rd Avenue Northeast and down through Northeast 16th Place as part of the Hydrogen Sulfide (H2S) Corrosion Control Program. Spring 2009
Hidden Lake Pump Station Replacement and Sewer Improvement -- The county replaced its existing 40-year-old Hidden Lake Pump Station with a new 6.8-million-gallon-a-day pump station and 12,000 feet of new sewer trunk line near Boeing Creek in Shoreline. The project increased system reliability by adding capacity that will help reduce overflows into Puget Sound during heavy rains. Other investments include a 500,000-gallon-capacity underground wastewater storage pipe in Boeing Creek Park and an upgraded a City of Shoreline stormwater detention pond. Spring 2009
Carnation Wastewater Treatment Facility -- The county constructed a new wastewater treatment plant that replaces aging septic systems in the City of Carnation. The plant serves about 2,000 people in Carnation's urban growth area, with capacity to serve up to 4,000 in 2030. At design capacity, the plant is expected to treat 480,000 gallons of wastewater a day.
Spring 2008
Murray Avenue Pump Station upgrade -- King County completed initial upgrades the station by installing new pumps and new mechanical and electrical equipment. Fall 2007
Densmore Stormwater System Improvement -- The county installed a stilling vault and ventilation pipe to better control stormwater and prevent overflows into the Lake Washington Ship Canal and Lake Union. The project included replacing the existing 36-inch-diameter drainpipe with one that's more stable and reliable.
Fall 2007
Bellevue Way Southeast Sewer Pipe Installation -- This new 500 foot sewer pipe underneath Bellevue Way Southeast and the access road in Mercer Slough Nature Park east of 113th Avenue Southeast improves the wastewater system's reliability and capacity.
Summer 2007
Fairwood Interceptor Sewer -- An aging pipeline in an area prone to erosion and landslides was replaced with a larger sewer line to improve water quality and slope stability around Madsen Creek, and to increase system capacity in the area.
Spring 2007
North Mercer Interceptor Emergency -- 2,300 feet of sewer pipe was replaced underneath Southeast 24th Street, 84th Avenue Southeast and Luther Burbank Park on Mercer Island following the pipe rupture in December 2006.
Spring 2007
Pacific Pump Station Replacement -- This pump station replaced an older station to carry increased wastewater flows from the City of Pacific to the South Treatment Plant in Renton.
Winter 2007
Vashon Treatment Plant Upgrade -- Upgrading the existing treatment plant increased capacity and added backup systems to meet regulations and protect human health and the environment.
Fall 2006
Matthews Park Pump Station and Sewer Improvement -- Since 2002, King County has completed three projects to upgrade aging infrastructure in the Matthews Beach area including upgrading the pump station, repairing corroded concrete inside the North Portal entrance to the Lake City Tunnel and repairing (slip lining) the Matthews Park force main.
Fall 2006
York Pump Station Standby Generator -- Construction of three standby generators at York Pump Station, located in Redmond, will insure a backup power source in the event of a power outage.
Summer 2006
Lincoln Park Sewer Line (Barton Force Main) Repair -- Relining of a 50-year-old sewer line that runs 6,250 feet through West Seattle's Lincoln Park after it was damaged during winter heavy storms. The project also included adding another 24-inch pipe along side the newly relined pipe to add capacity and allow periodic inspection of each of the lines.
Spring 2006
Henderson/M.L. King CSO Control -- A sewer project in the Rainier Beach community that will reduce overflows from sewers in the area that reach Lake Washington.
Fall 2005
Kamber Road Sewer Line Repair -- Repair of a 21-inch sewer line along Kamber Road in Bellevue next to East Creek are necessary because of ground settling and will protect public health and the environment. Summer 2005
Denny Way/Lake Union CSO Control -- Providing additional storage and treatment that will greatly reduce the number of untreated combined sewer overflows from the Denny Way wastewater regulator station.
Spring 2005
Sweyolocken Pump Station -- The updated Sweyolocken Pump Station, located next to Bellevue Way and the Mercer Slough Nature Park, handles increased flows. Winter 2005
North Creek Storage Facility -- Located in the City of Bothell, this new 6-million-gallon underground storage tank manages excess wastewater. Spring 2004
Ravenna Creek Stream Flow Transfer Pipeline --This pipeline takes clean water from Ravenna Creek that used to flow into a sewer line and moves it into a pipe that flows into Lake Washington. Winter 2004