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Duwamish/Diagonal Sediment Remediation Project

Introduction | Project Description | Contacts

Introduction

Duwamish/Diagonal CSO/SD Sediment Remediation Project, Closure Report, July 2005

Figure 1. Duwamish/
Figure 1. Duwamish/
Diagonal Vicinity Map.
(Click map for larger view.)

This Closure Report documents the work performed during the sediment remediation project at the King County Duwamish Combined Sewer Overflow (CSO) outfall and the City of Seattle Diagonal Way CSO/Storm Drain (SD) outfall (Duwamish/Diagonal CSO/SD) site on the Duwamish River in Seattle, Washington (refer to Figure 1). This Closure Report describes the dredging, transport, disposal, and capping methods which occurred between November 2003 and March 2004.

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Complete Report (no appendices) – 5.43 MB

Front Matter (title page and table of contents) 33.9 KB
Section 1 – Introduction 1.64 MB
Section 2 – Construction Activities 1.64 MB
Section 3 – Compliance Monitoring 1.57 MB
Section 4 – Surveys 597 KB
Section 5 – Deviation from Plans 18.7 KB
Section 6 – Post Construction Monitoring 567 KB
Section 7 – Affidavit 85 KB
Section 8 – References 18.7 KB
Appendix A – Photos (498 KB)
Appendix B – Contractor Daily Reports (3.32 MB)
Appendix C – King County Inspector Daily Reports (4.19 MB)
Appendix D – Lab Reports (2 MB)
Appendix E – Blue Water Engineering Surveys (766 kB)
Appendix F – Water Quality Monitoring Sampling and Analysis Plan (409 KB)
Appendix G – Sediment Monitoring Sampling and Analysis Plan (1.59 MB)

The project is part of the Elliott Bay/Duwamish Restoration Program, or EBDRP. The program is the result of a 1991 legal settlement reached by the City of Seattle and King County (then the Municipality of Metropolitan Seattle, or Metro) with the National Oceanic and Atmospheric Administration, or NOAA.

The settlement projects include sediment remediation, habitat development and improvements, and pollution source-control measures. The U.S. Fish and Wildlife Service, Washington State Department of Ecology (Ecology), Suquamish Tribe, Muckleshoot Tribe, NOAA, City of Seattle and King County administer the program and make up the EBDRP Panel.

The U.S. Environmental Protection Agency, Ecology, King County and City of Seattle are working together on source control , project planning and design for the Duwamish/Diagonal Sediment Remediation Project.

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Project Description

The initial study for this project, issued in January 2002, proposed a cleanup area of about 5 acres. In February 2002 during public review of the study, comments were received that recommended expanding the site to include another site upstream. After further evaluation, the EBDRP Panel expanded the project.

The project site is on the east side of the Duwamish River, upstream of Harbor Island and immediately downstream of Kellogg Island in the lower portion of the Duwamish River. The site is within the south industrial section of Seattle.

The original area extends about 750 feet along the shoreline upstream and downstream of the Duwamish/Diagonal Way outfalls. It is 260 feet wide. The added site extends about 500 feet along the shoreline upstream and downstream of the former Diagonal Avenue Treatment Plant outfall and the Diagonal Avenue South storm drain outfall. It is 160 feet wide and does not touch the shoreline.

The project isolated contaminated sediment near four outfall pipes on the Duwamish River in Seattle:

  • Diagonal Way storm drain
  • Duwamish combined sewer overflow
  • the former Diagonal Avenue Treatment Plant outfall
  • Diagonal Avenue South storm drain.

The King County Department of Natural Resources and Parks managed the project. Work was done by Miller Contracting and JE McAmis. The project isolates contaminated sediment from the environment by building an isolating sediment cap. A layer of contaminated sediment at least 3 feet thick will be mechanically dredged from the site to provide the space needed to install the isolating sediment cap without increasing the existing bottom elevations.

The areas dredged contained polychlorinated biphenyls, or PCBs, but all dredged sediment (66,000 cubic yards) was below the Toxic Substances Control Act (TSCA) PCB limit. The contaminated sediment handled by Rabanco waste disposal and shipped by train to the Roosevelt Landfill in Klickitat County.

A follow up action was conducted in February 2005. A thin layer of sand was placed around the dredged area to reduce the level of contaminants from previous dredging activity.

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Contacts

For questions about this Web site, contact John Phillips by e-mail or at 206-263-6543.

Department of Natural Resources and Parks
Wastewater Treatment Division
201 S. Jackson St., Suite 505
Seattle, WA 98104-3855

 

For questions about the Wastewater Treatment Division Web site, please send an e-mail message.

 

Updated: Oct. 31, 2005
 

  

Related Information:
Duwamish Waterway Programs

Elliott Bay/Duwamish Restoration Program

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