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Toxics Cleanup Program

Lower Duwamish Waterway
Source Control Investigation

Slip 6
River Mile 3.9-4.4 East

Site BackgroundPlease cllick on map above, then click on the small gold square in the bottom right hand corner to view a larger size..

The former Slip 6 Source Control Area is located along the eastern side of the LDW Superfund Site.  It sits 3.9 to 4.4 miles from the southern end of Harbor Island.  The map shows the areas of interest which include: the former Paccar site, the former Rhone-Poulenc site, the Museum of Flight, a portion of the Boeing Developmental Center, and a portion of the King County International Airport.

The upland areas next to Slip 6 have been heavily industrialized for decades.  Historical and current commercial and industrial operations in the area of Slip 6 include cargo handling and storage, auto storage lots, truck manufacturing, chemical processing, aviation operations, and airplane parts manufacturing.  The nearest residential area is about one-half mile to the southwest across the LDW.


Sediments in the Slip 6 portion of the LDW have been contaminated by various sources and chemicals.  The contaminants first affected upland media including surface water, groundwater, soil, and air before reaching the LDW sediments.

The following chemicals are considered to be contaminants of concern with regard to potential sediment recontamination.

Metals Organics
Mercury PCBs
Copper Dibenz(a,h)anthracene
Lead Phthalates (butyl benzyl phthalate)
Tin Volatile Organic Compounds (VOCs)
Arsenic Semivolatile Organic Compounds (SVOCs)
Chromium Petroleum Hydrocarbons

8801 East Marginal Way South Site (a.k.a. Kenworth Truck Co. Site)

This site is located at 8801 East Marginal Way South, in Tukwila, Washington on the east bank of the Lower Duwamish Waterway.  This site is bordered to the north by property owned by The Boeing Company, to the south by property owned by Container Properties, LLC (formerly the Rhone-Poulenc site) and the Museum of Flight Foundation, to the east by East Marginal Way South and to the west by the Lower Duwamish Waterway.

Ecology negotiated an Agreed Order to address the upland area of the site with PACCAR Inc and Merrill Creek Holdings LLC, the potentially liable parties (PLPs).  Under this Agreed Order, the PLPs will update and implement an Interim Action Work Plan for the upland portion of the site.

Click here for more information on the 8801 East Marginal Way South site.

Source Control

Ecology is the lead for source control for the LDW Superfund site.  Source control is the process of finding and then stopping or reducing releases of pollution to the river.  Ecology looks at the Slip 6 drainage basin to determine what sources need to be controlled (see map).  The routes for contaminants to Slip 6 sediments include: direct discharges via piped outfalls, bank erosion from adjacent properties, surface runoff from adjacent properties, groundwater discharge, air deposition, and spills directly to the inlet.

Source Control Action Plan

Ecology developed a Source Control Action Plan for Slip 6 which describes what source control actions are necessary. As part of the Source Control Action Plan, Ecology hired a contractor to put together a Summary of Existing Information and Data Gaps report.