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King County has been working for decades to clean up the Lower Duwamish.

View source control plan, reports and studies.

The County’s current efforts include:

  • Household Hazardous Waste Disposal Program - The County and its local partners have created the nation’s first program targeting consumer products a source of toxic chemicals.
  • Industrial Waste Program  – The King County Industrial Waste Program assists hundreds of businesses and property owners in maintaining regulatory compliance and utilizing best practices to address hazardous waste, spills and potential contamination sources on their property.
  • Business inspections – As part of the Washington State Department of Ecology’s Urban Waters Initiative , King County has partnered to conduct more than 1000 business inspections to reduce pollution entering the waterway.
  • Source Control Work Group – As a member of the interagency Source Control Work Group headed by the Washington State Department of Ecology, King County contributes to new contaminant studies and source control initiatives affecting the Lower Duwamish, and shares their findings with community stakeholders.

King County's Source Control Implementation Plan & Annual Reports

King County’s Source Control Implementation Plan (2014-2018) builds on over 50 years of investments made by King County to clean up the Duwamish River. The plan documents ongoing and priority source control actions and programs, and the County’s coordinated source control efforts with external partners. This plan is a draft that may change after being reviewed by the Department of Ecology. King County is currently implementing the plan. 

Lower Duwamish Waterway Source Control Implementation Plan , (3.2MB), Revised Draft: January 2016

The report offers information on the County’s continued commitment in the following areas:

  • Regulating and monitoring Duwamish area businesses that that send wastewater to the County sewer system  (refer to Section 2.1)
  • Protecting Our Waters - King County’s long-term plan to control combined sewer overflows (CSOs) (refer to Section 2.1)
  • Scientific assessments of pollution sources, including  sampling, source tracing and system mapping (refer to Section 3.0)
  • Managing and implementing the County’s Phase I Municipal Stormwater permit, and compliance with water and air quality permits and regulations at County facilities (refer to Appendix B)

Lower Duwamish Waterway Source Control Annual Report. This annual report documents source control related activities conducted by the County per our LDW Source Control Implementation Plan. This includes source tracing data, summaries of business inspections, and source control actions within the County jurisdiction and authority.

King County's pollution source control studies and plans - ongoing

Lower Duwamish Waterway Source Tracing in King County Combined Sewer System Sampling and Analysis Plan , August 2011. This work supports King County Source Control Implementation Plan for the Lower Duwamish Waterway Superfund site. King County performs this work to help identify sources of chemicals of potential concern and as a line of evidence to be used in evaluating whether these chemicals are present in sufficient amounts to potentially recontaminate sediments in the LDW.

Green River PCB Equipment Blank Study Sampling and Analysis Plan , April 2015. This study evaluates the potential for sampling equipment to cause contamination in samples analyzed for low level PCBs. Equipment blank samples collected for previous studies suggest that autosampler equipment may be contributing PCBs to surface water samples collected from the Green River watershed. The study is intended to better understand specific PCB congener contamination from autosampler equipment and evaluate the potential bias to Middle and Lower Green River surface water samples collected in previous King County Green River Watershed studies. 

King County's pollution source control studies and plans - completed

Lower Duwamish Waterway Source Control Brandon Combined Sewer Basin Study Data Report, May 2016. This data report presents the results of a pilot study conducted within the Brandon Combined Sewer Basin, which can discharge to the Lower Duwamish Waterway during substantial rainstorms. Combined sewer basins include inputs from domestic and industrial wastewater (sewage), groundwater infiltration into combined sewer lines, and stormwater. This pilot study looked at how much pollution is entering the Brandon Combined Sewer Basin pipes during a rainstorm, and asks does it primarily come from sewage, stormwater, or groundwater? The results of this study are intended to be useful in guiding any basin-wide source tracing efforts in combined basins prior to CSO control.

Brandon Study Fact Sheet

Brandon Study Data Report , May 2016

Supporting appendices:

Lower Duwamish Waterway Source Control Brandon Combined Sewer Basin Study Sampling and Analysis Plan , August 2011

Duwamish River Basin Combined Sewer Overflow Data Report for Samples Collected from September 2007 to January 2010.
This data report presents the analytical results for combined sewer overflow (CSO) samples collected within the Duwamish River Basin. The goal of King County's CSO survey was to collect samples that represent CSO conditions from the Duwamish River Basin and to analyze these samples for polychlorinated biphenyls (PCBs), semi-volatile organic compounds (SVOCs), select metals and conventional parameters. Resulting data will allow King County to further characterize concentrations of these parameters during CSO conditions for the Duwamish Basin. These data can be used in source control evaluations for the Duwamish Waterway and East Waterway Superfund Sites.

CSO Data Report , December 2011
Supporting appendices:

Duwamish River Basin, Combined Sewer Overflow Survey, Sampling and Analysis Plan , October 2007, Draft

Lower Duwamish Waterway Source Control: Supplemental Bulk Atmospheric Deposition Study Final Data Report. This study supplements the previous bulk air deposition study by collecting additional measurements of chemical air deposition in the Duwamish River Valley and on Beacon Hill in Seattle. A station in Georgetown was added and more samples for PCB and dioxin/furan congener analyses were collected to increase statistical power. Combined data from the main and supplemental studies were analyzed in this report.

Air Deposition Fact Sheet , June 2015

Supplemental Bulk Air Deposition Report , May 2015
Supporting appendices:

Lower Duwamish Waterway Bulk Atmospheric Deposition Study Sampling and Analysis Plan - 2013 Addendum , April 2013

Lower Duwamish Waterway Source Control: Bulk Atmospheric Deposition Study Final Data Report. This study measured bulk (dry particulate and rainfall) air deposition of chemicals of potential concern at locations in the Green/Duwamish Watershed during 2011 and 2012. The objectives of this study were to measure bulk air deposition in areas of different land use and development density, and to further understanding of atmospheric deposition sources to the Lower Duwamish Waterway.

Air Deposition Data Report , December 2013
Supporting appendices:

Lower Duwamish Waterway Bulk Atmospheric Deposition Study Sampling and Analysis Plan , August 2011

Lower Duwamish Waterway Source Control: Green River Watershed Suspended Solids Data Report: This study characterizes chemical concentrations in suspended solids and the differences of suspended solids quality between major tributary basins and the Green River during both dry conditions and wet season/storm events. The study focuses on key contaminants of concern for the Lower Duwamish Waterway Superfund site: arsenic, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and dioxins/furans. While this study does not estimate contaminant loading to the Lower Duwamish Waterway, the data can be used to help characterize the contaminants transported from the Green River to the Lower Duwamish Waterway. The results can also be used to help guide source control efforts; for example, identification of basins with elevated contaminant concentrations.

Green River Watershed Suspended Solids Data Report: December 2016 (4MB)

Supporting appendices:

Green River Study: Suspended Solids Characterization Sampling and Analysis Plan: January 2013

Sediment Quality in the Green River Watershed. This study measured chemical concentrations in stream sediments in the Green River Watershed. The objectives of this study were to characterize chemical concentrations in stream sediments and to better understand the relative differences of sediment quality between tributary basins and the Green River. The sediment data will also provide information to assist in understanding upstream sources of chemicals to the Lower Duwamish Waterway.

Lower Duwamish Waterway Source Control: Green River Watershed Surface Water Data Report. This study measured surface water concentrations of arsenic, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in samples collected in 2011 and 2012 from four major tributaries to the Green River (Newaukum, Soos and Mill creeks and the Black River), as well as at two locations on the main stem Green River: an upstream location at Flaming Geyser State Park (upriver of the tributary sampling sites), and a downstream location at Foster Links Golf Course (downstream of the tributaries).The objectives of this study were to: (1) better understand the relative contribution of arsenic, PAHs and PCBs to the LDW from upstream areas in the Green River and (2) evaluate the relative spatial differences between sampling sites and differences in dry season baseflow and wet season storm event conditions.

Lower Duwamish Waterway Source Control: Upper and Middle Green River Surface Water Data Report. This study measured surface water concentrations of arsenic, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in samples collected in 2013 and 2014 from three sites: two were approximately 20 miles above the Howard Hanson Dam in the upper reach of the Green River; and one was below the Dam in the middle reach of the Green River at Kanaskat-Palmer State Park. The objectives of this study were to: (1) better understand the relative contribution of arsenic, PAHs and PCBs to the lower reaches of the Green River as well as LDW from upper and middle reaches of the Green River; and (2) evaluate the relative spatial differences between sampling sites and differences in dry season baseflow and wet season storm event conditions.

King County Atmospheric Deposition Sampling 2005-07 (PAHs; PCBs; Phthalates)

Report (PDF file, 2MB)

King County Sampling 2003-06 (Phthalates; Benzyl Alcohol)

King County International Airport Sampling 2006 (PAHs, PCBs, Phthalates, metals)

Phthalate Source Study, 2003 - 2005

Because the presence of phthalates in the environment is an emerging issue of national and international scope and is beyond any one agency's capability to solve, staff of King County and the City of Seattle joined with the City of Tacoma in 2003 to test various commonly used products and materials to help identify the source of these chemicals. For additional information, refer to the "Phthalate Source Study" in the following progress reports:

  • June 2005  (pages 15-17), Initial results of passive air deposition sampling
  • January 2005  (pages 11-13), Phthalate air monitoring -- sampling and analysis plan for passive air deposition sampling;
  • June 2004  (pages 16-20), Report on products tested.

King County participation, Sediment Phthalates Work Group (2007-08): The cities of Tacoma and Seattle, King County, Ecology, and U.S. Environmental Protection Agency work together to better understand how phthalates are reaching Puget Sound sediments and what are the related impacts to humans and animals. The work group evaluated existing information regarding phthalate sediment concentrations, identify data gaps, and recommend possible short-term actions. It also described possible ways to address long-term issues.

These progress reports describe the status of source control activities completed by King County and Seattle Public Utilities as part of the Lower Duwamish Waterway Superfund cleanup.

June 2005 Progress Report
(Reporting period: January - June 2005)
Entire report , without figures (1.9 MB)
Table of contents
Figure 1-25 (5.7 MB)
Appendix C, Figure 1
Appendix C, Photos

January 2005 Progress Report
(Reporting period: June - December 2004)
Entire report, without figures (2.6 MB)
Table of contents
Figure 1-17 (4.9 MB)
Figures D-1 and D-2

June 2004 Progress Report
(Reporting period: January 2003 - June 2004)
Entire report, without figures (7.8 MB)
Table of contents
Figure 1-8 (4.3 MB)