Lower Duwamish Waterway
Source Control Investigation

1st Avenue South Storm Drain
Click on map to view larger size.River Mile (RM) 2.1 West

Site Background 

The 1st Avenue South Storm Drain source control area is located along the western side of the Lower Duwamish Waterway (LDW) Superfund Site at RM 2.1 as measured from the southern end of Harbor Island. The source control area is south of the Port of Seattle’s Terminal 115, east of Highland Park Way SW, west of the Trotsky Inlet and Riverside Drive source control areas, and extends south to SW Roxbury Street.
 
The 1st Avenue S Storm Drain source control area is unique in that there are no facilities located directly adjacent to the LDW. Adjacent properties to the southeast and northwest are addressed as part of other source control areas. Stormwater in the 1st Avenue S storm drain basin is transported via underground pipes and surface ditches to a series of wetlands which discharge to an intertidal slough under the 1st Avenue S bridge.
 
There are 72 upland facilities in the 1st Avenue S SD source control area that are listed in Ecology’s Facility/Site Database.  These properties and facilities could affect sediments at RM 2.1 West.
 
The 1st Avenue S SD is located almost entirely within the 8th Avenue S CSO basin, which discharges to the LDW in the Riverside Drive source control area. Discharges from the 8th Avenue S CSO are addressed in the Data Gaps Report for the RM 2.2 to 3.4 West (Riverside Drive) source control area.

Contamination

Sediments in the 1st Avenue South Storm Drain 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 in the 1st Avenue South Storm Drain source control area because they could possibly recontaminate Lower Duwamish Waterway sediments once it has been cleaned up.

Metals Organics
Mercury Polychlorinated biphenyls (PCBs)
  Dioxins/Furans  
  Phthalates
  Other semi-volatile organic compounds


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.

Potential sources of sediment recontamination associated with the 1st Avenue South Storm Drain source control area include SD outfalls and discharges from upland properties. Transport pathways that could contribute to the recontamination of sediments associated with the 1st Avenue South Storm Drain source control area following remedial activities include direct discharges to, or surface runoff (sheet flow) from, properties adjacent to the wetlands. Bank erosion, groundwater discharges, air deposition, and spills to the wetlands may also contribute to the recontamination of sediments.

Source Control Action Plan

Ecology is developing a Source Control Action Plan for the 1st Avenue South Storm Drain source control area. This plan describes the source control actions that are necessary to reduce the potential for 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