King County’s long-standing commitment to the Duwamish

King County believes cleaning up the Lower Duwamish is the right thing to do. The County has worked for decades to restore the waterway by investing in habitat restoration, water quality improvement, pollution controls and sediment cleanups. These investments in pollution control and CSO reduction projects have successfully removed decades of contamination from some of the waterway's most contaminated areas.

Duwamish Waterway timeline

The Duwamish is cleaner today than it has been in nearly a century. Highlights of King County's efforts to restore the waterway to health include:

• Click here for 5 key benchmarks in King County/Duwamish sewer history
• Click here to explore 7 Metro/King County sewer system improvements’ effects on the Duwamish
• Click here for 6 Metro/King County pollution prevention/cleanup projects in the Duwamish
• Click here for key fish health benchmarks on the Duwamish
• Click here for 4 major Duwamish River water quality studies and planning
• Click here for 4 projects to restore the habitat of the Duwamish

Or just scroll down to scan King County work to protect and restore the Duwamish.

1958: Metro was born after a citizen initiative was passed with 58 percent of Seattle’s vote and 67 percent of the suburban area vote. Voters authorized Metro to build and operate regional sewage treatment and water quality facilities to address the worsening pollution of Lake Washington and other local waters.
>> Click here for next key benchmark in King County/Duwamish sewer history.

1958: Duwamish River water quality studies: The newly-formed agency, Metro, (later to merge with King County) charged with cleaning up local water bodies, begins multiple water quality studies in the Green/Duwamish River.
>> Click here for next water quality study entry.

1963: Metro (later to merge with King County) finds that levels of dissolved oxygen in Green/Duwamish River to be dangerously low for fish: Summer levels of dissolved oxygen in the Green/Duwamish River were found to be far below minimum requirements for fish because of discharges of untreated wastewater and stormwater over the previous 50 years.
>> Click here for next fish health study.

1964: A 17-year Green/Duwamish River water quality study begins: Metro begins 17 years of continuous data collection on water quality.
>> Click here for next water quality study entry.

1965: Sewage and stormwater from along the Green/Duwamish River will be sent to a sewage treatment plant - and as Metro (later to merge with King County) completes its wastewater treatment plant in Renton. (effluent discharged into the Green River.
>> Click here for next sewer system improvement affecting Duwamish.

1967: Metro completes the East and West Marginal Way Interceptor Sewers, which diverts industrial effluent (wastewater) from the Duwamish to the West Point Treatment Plant.
>> Click here for next sewer system improvement affecting Duwamish.

1968: Voter approve spending $1.4 million investment to separate storm and sanitary sewer systems and improve drainage. Separated sewers and improved drainage reduce the volume of stormwater and wastewater discharged directly to the waterway.
>> Click here for next sewer system improvement affecting Duwamish.

1969: Metro launches the Industrial Waste Pretreatment Program regulating industries to remove toxicants before discharging their wastewater into the sewer system.
>> Click here for next sewer system improvement affecting Duwamish.

1969: The Diagonal Way Treatment Plant was closed, eliminating its discharge of treated wastewater to the Lower Duwamish Waterway.
>> Click here for next sewer system improvement affecting Duwamish.

1970: Metro (later to merge with King County) begins ongoing monitoring of water quality in the Green/Duwamish River to chart trends and to detect emerging problems.
>> Click here for next water quality study entry.

1972: The federal Clean Water Act becomes law it is the cornerstone of surface water quality protection in the United States.
>> Click here for next key benchmark in King County/Duwamish sewer history.

1973: The Kent lagoons are closed and wastewater was transferred to the South Treatment Plant in Renton, no longer going into the Duwamish.
>> Click here for next sewer system improvement affecting Duwamish.

1976: Studies show that dissolved oxygen concentrations in the Green/Duwamish River have greatly improved since the 1960’s when Mtwero bregan improvements on the Duwamish. (Dissolved oxygen concentrations have increased by a factor of 4 since the 1960s.)
>> Click here for next fish health study.

1977: The Auburn lagoons were closed and wastewater was transferred to the South Treatment Plant in Renton.
>> Click here for next sewer system improvement affecting Duwamish.

1978: Metro’s first water comprehensive quality plan – Metro (later to merge with King County) issues the first comprehensive water quality plan for the Cedar and Green River basins.
>> Click here for next water quality study entry.

1980: Metro part of first program in the country to target consumer products as a source of toxic chemicals. Metro and area jurisdictions begin planning the Household Hazardous Waste Disposal Program.
>> Click here for next King County pollution prevention project.

1980: Duwamish dissolved oxygen concentrations continue to improve - increasing from 4 mg/L to 7 mg/L since the 1960’s.
>> Click here for next fish health study.

1983: Metro issues the Duwamish Clean Water Plan, addressing pollution problems in the lower river.
>> Click here for next King County pollution prevention project.

1985: Elliott Bay Action Program: EPA and Ecology, working with City of Seattle, Metro, the Port of Seattle, and others began the Elliott Bay Action Program, a large multi-year comprehensive program focusing on toxic sediment contamination, its sources, and solutions for cleanup in Elliott Bay and the Lower Duwamish Waterway. (This program was part of the Urban Bay Action Program of the multi-agency Puget Sound Estuary Program.)
>> Click here for next King County pollution prevention project.

1986: Metro began work on a new outfall for the South Treatment Plant in Renton so that treated wastewater discharges could be diverted from the Green River into Elliott Bay.
>> Click here for next sewer system improvement affecting Duwamish.

1986: A $1.1-billion secondary treatment/combined sewer overflow control plan: the Metro Council (Metro will later merge with King County) amends the Comprehensive Sewerage Plan by adopting a $1.1-billion secondary treatment/combined sewer overflow control plan to help reduce the impacts of a growing population in the central Puget Sound area.
>> Click here for next key benchmark in King County/Duwamish sewer history.

1987: Metro and the City of Seattle complete the Hanford separation project, reducing combined sewage/stormwater flows to the Diagonal Way storm drain (and into the Duwamish) by two-thirds.
>> Click here for next sewer system improvement affecting Duwamish.

1990: Dissolved oxygen concentrations in the Duwamish had increased to 10 times the levels of the 1960s, greatly improving fish health.

1991: Elliott Bay/Duwamish Restoration Program is established: A federal consent decree establishes the program, with the City of Seattle and King County required to spend approximately $24 million on habitat restoration, sediment cleanup, and source control projects.
>> Click here for next key benchmark in King County/Duwamish sewer history.

1992: Metro’s Lander Sewer Separation Project adds 1.4 million gallons of storage capacity to further reduce combined sewer overflows into the Lower Duwamish..
>> Click here for next sewer system improvement affecting Duwamish.

1994: Metro merges with King County.

1996 – 1998: King County undertakes an extensive study: “King County Combined Sewer Overflow Water Quality Assessment for the Duwamish River and Elliott Bay,” to have a better understanding of the dynamics of the estuary and the impacts of CSOs relative to other pollutant sources. Study team includes scientists, planners, engineers, and other professionals; a stakeholder committee (composed of representatives from local communities, businesses, environmental organizations, tribal governments, and agencies); and a national peer review panel.

1999: King County’s Regional Wastewater Services Plan is approved – including extensive public involvement and review, the plan was approved for work to control many county CSOs in Seattle, including five that required control in the Lower Duwamish Waterway. Five additional projects are planned to begin in 2012.

1999 – 2000: Hamm Creek Habitat Restoration Project: together with the U.S. Army Corps of Engineers, King County creates 2,300 feet of new riparian stream bed and channel for Hamm Creek. EBDRP designs and monitors a one- acre estuarine marsh with fish-passable connection to the Duwamish Waterway. The enhanced freshwater Hamm Creek channel features meanders, fish pools, and large woody debris. The intertidal habitat is planted with native estuarine marsh vegetation in spring 2000.
>> Click here for next habitat restoration entry.

2000: Herring's House Park and Intertidal Habitat Restoration Project. This project was completed in 2000, except for monitoring, which continues. The work has included removal of mill structures, a shoreline dock, and contaminated sediments. A 1.8 acre intertidal bay was created, with fringing emergent vegetation in an intertidal zone. Riparian vegetation was also planted to create a riparian buffer.
>> Click here for next habitat restoration entry.

1999 – 2000: North Wind's Weir Restoration Project: In a project at Cecil B. Moses Park, a one-acre basin is created to provide off-channel habitat for out-migrating salmonids. Emergent and riparian vegetation is planted.
>> Click here for next habitat restoration entry.

1999: Norfolk combined sewer overflow sediment remediation project: King County removes 5,190 cubic yards of contaminated sediment near the county’s Norfolk CSO. The project was monitored for a period of five years. The EPA, Ecology, King County and City of Seattle worked together on source control, project planning and design for the project.
>> Click here for next key benchmark in King County/Duwamish sewer history.

2000: Lower Duwamish Waterway Group forms to investigate Duwamish sediments: The Boeing Company, the City of Seattle, King County, and the Port of Seattle (the Lower Duwamish Waterway Group or LDWG) complete a voluntary agreement to begin investigation of the Lower Duwamish Waterway sediments, toward an ultimate waterway cleanup plan.

2002 – 2005: King County's Diagonal/Duwamish dredging removes 66,000 cubic yards of contaminated sediment from the Lower Duwamish.

2006: Turning Basin No. 3. Restoration Project. This project is located on the former Kenco Marine Services property. An old building, dock, and grounded barges were removed. Fill material was removed to push back the shoreline. Marsh and riparian vegetation were planted. The project was completed in April 2006, with monitoring for intertidal habitat success being conducted through 2015.

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