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Toxics Cleanup Program

Slip 1 
River Mile (RM) 0.9-1.0 East

Site Background

Click on photo for larger view.The Slip 1 Source Control Area is located along the eastern side of the Lower Duwamish Waterway (LDW) Superfund Site between 0.9 and 1.0 miles from the southern end of Harbor Island.  The map shows the area of interest which is bordered on the east by East Marginal Way South.  The facilities located within this source control area are:

  • U.S. General Services Administration (GSA)-Federal Center South (commonly known as Federal Center South),
  • Snopac Products, Inc., and
  • Manson Construction Company

The upland areas near the Slip have been heavily industrialized for decades.  Historical and current commercial and industrial operations in the area of Slip 1 include automobile manufacturing, missile manufacturing, food products manufacturing and distribution, and construction services. 


Sediments in the Slip 1 portion of the LDW have been impacted by chemical contaminants from various sources. Before reaching the LDW sediments the contaminants first affected upland media including surface water, groundwater, soil, and air.

The following chemicals are considered to be contaminants of concern at Slip 1 because they could possibly recontaminate sediment once it’s cleaned up.

Metals Organics
Arsenic PCBs
Cadmium Polynuclear Aromatic Hydrocarbons (PAHs)
Bis (2ethylhexyl) phthalate 
Copper Dioxins 
Lead Furans
Zinc Semivolatile Organic Compounds (SVOCs) (1,2,4-trichlorobenzene, benzoic acid, dibenzofuran)

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 as much as possible releases of pollution to the river. Ecology looks at the drainage for Slip 1 in order to determine what work needs to be done for source control.  The Slip 1 drainage basin outlines the area where sources need to be controlled (see map). The way contaminants enter Slip 1 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 1.  This plan describes the source control actions that are necessary to prevent sediment recontamination.  As part of the Source Control Action Plan, Ecology hired a contractor to put together a Summary of Existing Information and Data Gaps report.

Related Information

Additional Resources