Boeing Isaacson Thompson

Updated April 2025

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November 2024 Blog: "Cleaning up: Join the conversation on the Boeing Isaacson Thompson cleanup site"

Ecology held a public comment period (Oct. 21 - Nov. 19, 2024) for review of several documents for the Boeing Isaacson Thompson cleanup site (Site) located at 8701 E Marginal Way S. in Tukwila on the Lower Duwamish Waterway (LDW) near Seattle’s South Park Neighborhood and the King County International Airport. 

View the comments we received and our responses. 

The following documents were available for review and are being finalized:

• Cleanup Action Plan: Ecology’s plan describing the cleanup work to address contamination at the Site. 
• Agreed Order: Legal agreement between Ecology and The Boeing Company (Boeing) requiring design of the work described in the cleanup action plan. 
• State Environmental Policy Act – Determination of Non-Significance: Ecology’s determination that the cleanup work is not likely to harm the environment. 

If you have questions about this site and others along the LDW! Join us at Community Office Hours. 
View the office hours schedule.
We are offering bi-monthly community office hours in 2025 at different locations in Georgetown and South Park. Drop-in to talk with cleanup site managers, outreach, and technical staff about the Lower Duwamish Waterway cleanup. Phone interpretation available in Spanish, Chinese, Vietnamese, and Khmer. All ages welcome!

Sign-up for Ecology's Monthly LDW Newsletter. Receive updates about Ecology's work along the LDW. Unsubscribe at any time. 

This Site is along the Lower Duwamish Waterway Superfund Site, which consists of a 5-mile stretch of the Duwamish River. The U.S. Environmental Protection Agency (EPA) added the LDW Superfund Site to the Superfund National Priorities List in 2001. Ecology is working to stop or reduce sources of contamination to the LDW Superfund Site, an effort known as “source control,” so that the EPA can proceed with the cleanup of the river sediment. This site is located in the Upper Reach, the area of the river that will begin sediment cleanup as early as 2024. The sediment cleanup adjacent to this Site have been deferred to align with the uplands cleanup to ensure the sources are sufficiently controlled.

The Model Toxics Control Act (MTCA) is Washington’s environmental cleanup law. It provides requirements for contaminated site cleanup and sets standards that protect human health and the environment. Ecology enacts the MTCA and oversees cleanups. The MTCA site cleanup process is completed in steps over a variable timeline.

Ecology will consider all comments received during the Oct. 21 - Nov. 19, 2024 public comment period and may make changes to the documents.  If the documents require significant changes, we will hold another public comment period.

If no significant changes are made, Ecology will finalize the documents and Boeing will begin designing the cleanup. Any new or amended legal agreements will be available for review during a future public comment period.

Current Boeing Isaacson Thompson cleanup site Public Participation Plan

This plan includes information for the public regarding opportunities to get involved in the Site cleanup process. The outreach activities and mechanisms presented reflect Ecology’s current plans for keeping the public informed and for receiving information and comments from the public. 

Site background

The Boeing Isaacson Thompson cleanup site is located in an industrial area of Tukwila on the east bank of the Lower Duwamish Waterway (LDW). The cleanup site is comprised of two properties owned by The Boeing Company and one property owned by the Port of Seattle. (See figure above)

The site is a former tidal marsh area which was reclaimed when the Duwamish River was straightened and channelized to form the current Duwamish Waterway in the early 1900s. After dredging, the area was used as farmland and then for a variety of industrial purposes. The former Duwamish River channel (later Slip 5) in the middle of the site was filled over time with contaminated materials from unknown sources.

The Isaacson Property (northern portion)

• Prior to 1945: The Mineralized Cell Wood Preserving Company used a solution of arsenic and sulfate salts of copper and zinc to treat lumber. Sludge and chemicals remaining in the tanks were reportedly drained directly to the ground during tank cleaning. 
• 1984: Boeing purchased the 9.84-acre property from Isaacson Steel Company, which had owned the property since 1943.

The Port of Seattle Property (northwestern portion)

• 1960s: A wall, called a bulkhead, was built along the LDW and filled to reclaim about 50 ft of land between the waterway and the Isaacson property. This ½-acre parcel of land is owned by the Port of Seattle.

The Thompson Property (southern portion) 

• 1920s-1930s: Bissel Lumber Company operated on the property. 
• 1930s-1966: The inlet partially dividing the Isaacson and Thompson property, called Slip 5, was filled in over time with contaminated materials including smelter slag and fire brick material. 
• 1956: Boeing purchased the 19.35-acre property.

Nearby cleanup sites and source control information

The site is bordered to the east by East Marginal Way S, to the north by the Jorgensen Forge cleanup site, to the south by the 8801 E. Marginal Way S cleanup site. It is bordered to the east by East Marginal Way S and the King County Regional Airport, and to the west by the Lower Duwamish Waterway.

The Lower Duwamish Waterway drainage basin is divided into source control areas. This site is located within the Boeing Isaacson/ Central King County International Airport (river mile 2.8-3.7) source control area along the east bank of the river.

Contamination
Investigation have found the following contamination above WA State cleanup levels:  

• Soil: metals, semi-volatile organic compounds (SVOCs), polychlorinated biphenyls (PCBs), petroleum hydrocarbons
• Groundwater:  metals, volatile organic compounds (VOCs), PCBs