image:filtered light in the forest

Toxics Cleanup Program

Lower Duwamish Waterway
Source Control Investigation

Boeing Isaacson/Central KCIA
Early Action Area 6 - Former Slip 5

Early Action Area 6 aerial view.

Site Background

Early Action Area-6 (EAA-6) is located along the eastern side of the LDW Superfund Site between 3.7 and 3.9 miles from the southern tip of Harbor Island.  The map shows two properties next to EAA-6, the Boeing Isaacson site and the Boeing Thompson site.  In addition, stormwater from the central portion of King County International Airport drains to EAA-6 through a 48-inch public storm drain outfall.

EAA-6 is located near a former tidal marsh area which was reclaimed when the Duwamish River was straightened and channelized to form the current Duwamish Waterway in the late 1800s and early 1900s.  After dredging, the area was used as farmland.

In the 1920’s and 1930’s Bissel Lumber Company occupied the Boeing Thompson site to the south of former Slip 5. Around 1941, the United States Navy used the property just north of Boeing Isaacson and constructed steel melting, forging, and fabricating facilities that were known as Isaacson Iron Works Plant No. 2. The Isaacson Steel Company purchased the plant in the 1950s and expanded the steel fabrication facility to what is now the Boeing Isaacson property during the 1950s and 1960s.

From the 1930’s to the mid-1960’s portions of Slip 5 were filled. By about 1966, Slip 5 was completely filled as part of site development at Boeing Thompson. The Boeing Company purchased the Thompson property in 1957 and the Isaacson property in 1984.


Sediments in the Early Action Area-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.

Chart of contaminants of concernThe chemicals (see chart at right) are considered to be contaminants of concern with regard to potential sediment recontamination.

Boeing Isaacson Thompson Site

The Boeing Isaacson Thompson Site is located along the east side of the LDW at approximately river mile (RM) 3.7 to 3.9, as measured from the southern tip of Harbor Island. This site is situated between the LDW on the west, East Marginal Way S. road on the east, on the north by the Jorgensen Forge property and by the 8801 Site (former Kenworth Truck/Paccar property) on the south.

Contamination at this site is due to industrial operations and facility development.

    The contaminants of concern in the soil are:
    • Arsenic, Cadmium, Chromium, Lead, Mercury, Nickel, PCBs, Petroleum Hydrocarbons, Zinc
    The contaminants of concern in the groundwater are:
    • Arsenic, Barium, Chromium, Lead
    The contaminants of concern in the stormwater are:
    • Antimony, Arsenic, Lead, Petroleum Hydrocarbons
Click here for more information on the Boeing Isaacson Thompson site.