Lower Duwamish Waterway
Source Control Investigation
Slip 2 - Slip 3
River Mile 1.7-2.0 East
The RM 1.7-2.0 East source control area is also referred to as Slip 2 to Slip 3.
This source control area is located along the eastern side of the LDW Superfund
Site between river mile 1.7 and 2.0 as measured from the southern end of Harbor
Island. Several facilities in this source control area are located directly
adjacent to the Lower Duwamish Waterway. From north to south, these facilities
- Glacier Northwest, Inc.(Glacier Northwest),
- Seattle Biodiesel,
- Samson Tug and Barge,
- Duwamish Marine Center.
Slip 2 is situated between Glacier Northwest and the Duwamish Marine Center.
Located to the east of these properties are East Marginal Way South and other
industrial facilities. To the north of Glacier Northwest is James Hardie Gypsum
and to the south and southeast of Duwamish Marine Center are the LDW, a vacant
lot owned by the Seattle Department of Transportation (DOT) and Slip 3.
There are six outfalls discharging storm water to the RM 1.7-2.0 East source
control area. These outfalls include four private and two public outfalls. One
of the public outfalls is the Michigan Street combined sewer outfall (CSOs).
Some areas of the Lower Duwamish Waterway are served by combined sewer systems,
which carry both stormwater and municipal/industrial wastewater in a single
pipe. These systems were generally constructed before about 1970 because it was
less expensive to install a single pipe rather than separate storm and sanitary
systems. Under normal rainfall conditions, wastewater and stormwater are
conveyed through this combined sewer pipe to a wastewater treatment facility.
During large storm events, however, the total volume of wastewater and
stormwater can sometimes exceed the conveyance and treatment capacity of the
combined sewer system. When this occurs, the combined sewer system is designed
to overflow through relief points, called combined sewer overflows (CSOs). The
CSOs prevent the combined sewer system from backing up and creating flooding
The locations of the outfalls located within the Slip 2-Slip 3 source control
area are shown on the map.
Sediments in the portion of the LDW near the RM 1.7-2.0 East source control
area 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
|| Phthalates (butyl benzyl phthalate)
|| Semivolatile Organic
||Poly Aromatic Hydrocarbons
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 RM 1.7-2.0 East (Slip 2-Slip 3)
source control area to determine what sources need to be controlled (see map).
The routes for contaminants to the sediments near this source control area
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 RM 1.7-2.0 East
(Slip 2-Slip 3) which describes what source control actions are necessary. As part of the
Source Control Action Plan, Ecology hired a contractor to develop a
of Existing Information and Data Gaps report.