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Toxics Cleanup Program

Lower Duwamish Waterway
Source Control Investigation

Norfolk CSO/SD
Combined Sewer Overflow/Storm Drain (CSO/SD)
Early Action Area 7

Photo showing shoreline and combined sewer overflow/storm drain locations at Norfolk CSO

Site Background

Norfolk CSO closeupEarly Action Area 7 was identified as an area requiring sediment cleanup based on work conducted for the Lower Duwamish Waterway (LDW) Superfund site.

This area is located between 4.9 and 5.5 miles from the south end of Harbor Island on the east bank of the waterway.  This site is next to the Norfolk CSO (see map).

The Norfolk CSO system is part of the regional wastewater system and discharges stormwater and untreated sewage during periods of heavy rainfall when the sewer system is inundated with water.  This system includes surface drainage for approximately 224 acres of mixed residential, commercial, and industrial property in the Lower Duwamish Waterway drainage basin.

EAA-7 was first identified as part of the Elliott Bay/Duwamish Restoration Program (EBDRP), which was established in 1991 to implement requirements of a Natural Resources Damage Assessment (NRDA) settlement and Consent Decree.  The EBDRP Panel was composed of Federal, State, and Tribal natural resource trustees, the King County Department of Natural Resources and Parks (KCDNRP) (then Metro), and the City of Seattle.  EBDRP settlement projects included sediment remediation, habitat development and improvements, and pollution source control measures. 

In 1999 the area around the Norfolk CSO outfall was dredged and backfilled with clean sediment. Three years of post-removal monitoring was conducted to evaluate the effectiveness of source-control measures that have been implemented.

The following compounds are identified as chemicals of concern in EAA-7 sediments:
  • Benzo(g,h,i)perylene
  • Bis(2-ethylhexyl)phthalate
  • Butyl benzyl phthalate
  • Hexachlorobenzene
  • PCBs
  • Metals

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 is looking at Early Action Area 7 in order to determine what work needs to be done to archive adequate Source Control.  The Early Action Area 7 drainage basin outlines the area where Ecology will be working (see map).  The routes for contaminants to Early Action Area 7 sediments may include: direct discharges via piped outfalls, bank erosion from adjacent properties, surface runoff from adjacent properties, groundwater discharge, air deposition, and spills directly into the river.

Ecology developed a Source Control Action Plan for Early Action Area-7 which describes the necessary source control actions.  As part of the Source Control Action Plan, Ecology hired a consultant to put together a Summary of Existing Information and Data Gaps report.  You can view both reports below .

Summary of Existing Information and Identification of Data Gaps Report

Early Action Area 7 Source Control Action Plan