Cleaning up contaminated sediments

Since 2000, the Lower Duwamish Waterway Group (LDWG) partners have worked under a voluntary agreement with the U.S. Environmental Protection Agency (EPA) and the Washington State Department of Ecology (Ecology) for a coordinated investigation of the Lower Duwamish Waterway (LDW) sediments. This investigation is called a Remedial Investigation/Feasibility Study (RI/FS). The RI, which began in 2001, was performed to determine the extent of contamination and risks for people and wildlife. The final report is available here.

In 2003, LDWG proposed areas for early action sediment cleanup to get an early start on reducing risks. Actions were taken at three of these most polluted sites (the Norfolk combined sewer overflow [CSO]/storm drain, the Duwamish/Diagonal Way outfalls, and Slip 4). Boeing demolished its former Plant 2 facility to clear the way for its cleanup and habitat restoration efforts. Cleanup is underway at Boeing Plant 2 and Terminal 117. Jorgensen Forge is next in line for early cleanup.

Based on information in the remedial investigation on the extent of contamination and on the associated human and ecological risks, LDWG prepared a feasibility study. The study examined different methods and alternative plans to clean up the contamination and reduce risk. The draft feasibility study was completed in 2009 and reviewed by the public. Based on public input, the draft final study was released on October 18, 2010. Members of the public, agencies, businesses and tribes submitted more than 1,300 comments during the public comment period. With the input received, EPA and Ecology published a final feasibility study in October 2012. The comment period on the proposed plan ended in June 2013, and the agencies are now waiting for EPA to issue a Record of Decision (ROD) to direct cleanup actions and long-term monitoring.

Controlling sources of contamination in the Duwamish Basin

King County, the City of Seattle, and the Port of Seattle (Port) are working with EPA and Ecology to control current sources of pollution into the LDW. The City of Seattle has a terrific video that demonstrates source control efforts for the Duwamish. Source control progress and data reports can be found here: SPU Source Control Efforts for Sediment Remediation Sites (Superfund). Other reports by King County can be found here: King County's pollution source control studies.

The Port invests about $2 million annually to manage the stormwater and source control programs for its properties. Efforts include complying with municipal and National Pollutant Discharge Elimination System (NPDES) permit requirements, source tracing, and cleaning out of stormwater systems. The Port has also voluntarily set up an Environmental Compliance Assessment Program that educates its tenants about compliance with stormwater and source control. A summary of the Port's environmental programs, including its stormwater management activities, can be found here: Port of Seattle Environmental Programs.

Besides working with businesses to control discharges into the waterway, the source control team has collected samples to identify sources of pollutants within the storm drain and combined sewer systems. It has also identified consumer products that may contain chemicals of concern found in waterway sediments.

So far, the partners have helped hundreds of businesses and property owners correct problems with hazardous materials, industrial wastewater, stormwater, spill containment, and leaking pipes. Here are some examples:

  • Between 2003 and 2005, Seattle and King County completed approximately 1,200 joint inspections at 750 businesses, primarily located in the Diagonal Ave South drainage/combined sewer basin. Since 2005, when Seattle took over stormwater inspections in the waterway, Seattle has completed 1,700 inspections at 700 businesses throughout the entire waterway area. Seattle inspectors continue to look at hazardous waste and industrial waste practices, but refer problems to the appropriate county or state agency for further technical assistance or enforcement.
  • Since the source control program began in 2003, corrective actions have been required at nearly 80 percent of the sites inspected. Spill prevention and stormwater problems together accounted for about 80 percent of the corrective actions identified by inspectors. The remaining corrective actions were made up of hazardous waste handling (19 percent) and industrial waste management-related problems (1 percent).
  • Since 2006, Seattle’s spill response team has responded to 120 spills in the Lower Duwamish Waterway.
  • Since 2004, Seattle has provided spill kits and technical assistance on spill control/containment to more than 300 businesses in the Lower Duwamish Waterway through its contractor, Resource Venture.
  • Seattle has installed sediment traps at 44 locations within 15 of the major publicly owned drainage systems. Traps are sampled every 6-12 months. As of December 2011, a total of 240 trap samples have been collected. In addition, Seattle has collected 180 inline and 330 catch basin grab samples from public and private drainage systems in the LDW. Ecology has been funding a large portion of Seattle’s source tracing efforts since 2009.
  • King County has installed sediment traps in 3 CSO basins, and collected inline sediment grab samples in all 7 CSO basins to identify current sources and aid in evaluating the effectiveness of source control efforts.
  • King County, Tacoma, and Seattle have sampled consumer products, such as detergents, motor oil, inks and cigarettes to determine whether they contained chemicals that are of concern in sediment, such as phthalates.
  • Seattle has jetted and cleaned more than 25,000 linear feet of storm drain and associated structures, removing approximately 1,000 tons of contaminated sediment that had accumulated in the system. SPU also routinely inspects and cleans catch basins throughout the waterway as part of its citywide operations and maintenance program.
  • In 2011, Seattle completed construction of a 5-acre stormwater wet pond/constructed wetland to treat runoff from approximately 224 acres in the Norfolk drainage basin.
  • In 2011, Seattle completed construction of a 5-acre foot stormwater wet pond/constructed wetland to treat runoff from approximately 224 acres in the Norfolk drainage basin.
  • King County has jetted and cleaned combined sewer lines and removed contaminated sediment to prevent overflow in two 2 CSO regulator facilities.

Businesses are also helping. For example, Boeing has been investigating sources of contaminants to stormwater contamination and has been conducting source control actions such as cleaning storm drain lines, excavating contaminated soil, and removing joint compounds (caulk) and paint that contain Polychlorinated biphenyls (PCBs) and metals. Boeing also installed state-of-the-art stormwater treatment systems at North Boeing Field and Plant 2.

Boeing continues to address source control for its facilities in the Duwamish basin under industrial stormwater general permits administered by Ecology through the state's stormwater program. Additional source control work for soils and groundwater is done through the corrective action process of the federal Resource Conservation and Recovery Act (RCRA) and standards of the state's Model Toxics Control Act (MTCA).

Restoring natural resources

The LDW Group partners are part of a large and growing group of residents, agencies, Tribes, and organizations that are actively working to protect and restore fish and wildlife habitat. Click here for a printable map of the many habitat restoration activities that have been accomplished or are underway in the LDW.

Since 1985, the Port has constructed 3.4 acres of aquatic habitat at six sites in the LDW, each involving the removal of previously placed fill to restore inter-tidal conditions, including approximately 1.8 acres of marsh and riparian habitat. Five public shoreline access sites have been improved in the past 20 years, totaling 9.7 acres and 5,100 linear feet of citizen access and native vegetation along waterway bank areas. The total cost of habitat and public use improvements exceeds $4 million. The Port has also set aside about 10 acres of wetlands and submerged lands and 20 acres of uplands in and around Kellogg Island as a preserve. Since 1991, King County and the City of Seattle have worked with natural resource agencies and Tribes on the Elliott Bay/Duwamish Restoration Program (EBDRP) to restore the Duwamish.

Boeing recently completed the largest habitat restoration in the Lower Duwamish Waterway, transforming nearly one mile of former industrial waterfront into a wetland resource that improves Puget Sound salmon runs.

Together, these entities have restored more than 55 acres of fish and wildlife habitat, including the following sites in the Duwamish:

  • 6.2 acres and 1,900 feet of riparian stream restoration on Hamm Creek
  • 5.7 acres of habitat restoration, including 1.8 acres of off-channel habitat at Herring's House
  • Nearly 5 acres of fish and wildlife habitat at Boeing’s former Plant 2 site
  • 0.74 acres of intertidal and subtidal habitat restoration in the Upper Turning Basin
  • 1 acre of off-channel habitat restoration at North Wind's Weir and Cecil B. Moses Park
  • 2 acres of off-channel habitat restoration at Site 1
  • 1 acre of intertidal and subtidal habitat at the Norfolk combined sewer overflow and storm drain following removal of 5,190 cubic yards of contaminated sediment
  • 11 acres of intertidal and subtidal habitat at the Duwamish combined sewer overflow and Diagonal storm drain following removal of 66,000 cubic yards of contaminated sediment and 4 acres of thin-layer placement

Removal with upland disposal involves transporting the dredged sediment by barge to a staging area where it would be loaded into rail cars for transport to an off-site regional landfill.

Greater sediment removal through dredging means greater permanence, but has higher costs and impacts over a longer period than other technologies. Also, for people and wildlife that eat resident seafood from the LDW, risks will likely remain high throughout the dredging period under any alternative. Seafood consumption advisories can help manage these increased risks to people, but not wildlife.

Removal with upland disposal would involve transporting the dredged sediment by barge to a staging area where the sediment would be loaded into rail cars for transport to an off-site regional landfill.