This page may be viewed in: English
Frequently Asked Questions
What is the LDW?
The Lower Duwamish Waterway (LDW) represents the last five miles of the Duwamish River before it splits into the East and West waterways to flow around Harbor Island and out to Puget Sound. In the early 1900s, as Seattle’s economy grew, the city changed its landscape. Dredging, filling, river diversion and rechanneling supported local industries and altered the natural flow of the Duwamish to form the Lower Duwamish Waterway that we know today.
What is the Superfund program and what does EPA stand for?
The U.S. Environmental Protection Agency’s (EPA) Superfund program is responsible for cleaning up some of the nation’s most contaminated land and responding to environmental emergencies, oil spills, and natural disasters. In 2001, the EPA listed the Lower Duwamish Waterway as a Superfund site under federal law. Since 2001, the members of LDWG have been committed to advancing the cleanup of the waterway under the direction of the EPA. Visit the EPA’s website here.
What is Ecology?
Washington State Department of Ecology (Ecology) is a state agency dedicated to preserving and protecting the environment in Washington. Ecology is responsible for leading efforts to control sources of pollution from the drainage area surrounding the Lower Duwamish Waterway (LDW) Superfund site. This includes overseeing the cleanup of upland contaminated sites in the watershed. EPA and Ecology work together to plan source control work in coordination with EPA’s sediment cleanup schedule. Visit Ecology’s website here.
What contaminants are found in the Lower Duwamish Waterway?
Pollutants found in the river sediment include heavy metals like arsenic, lead, and zinc, and other types of contaminants known as organics, including polychlorinated biphenyls (PCBs) and polyaromatic hydrocarbons (PAHs). Today, people who have frequent contact with contaminated sediment on the waterway bottom or who eat some types of fish and shellfish that live year-round in the waterway could be exposed to the pollution. Salmon from the Lower Duwamish Waterway are safe to eat. Read more here.
What is source control?
“Source control” refers to pollution prevention programs that prevent new and ongoing sources of pollution from getting into the river and harming the environment. Like all other urban waterways, the biggest ongoing source of pollution in the Duwamish today comes from stormwater runoff that carries chemicals from our cars, buildings, roads, businesses and yards. King County, the City of Seattle and Ecology are working together to find ways to control these sources of pollution. Read more.
What does CSO stand for and what is it?
Combined sewer overflows (CSOs) are relief points in older sewer systems found in most of Seattle that carry sewage and stormwater in the same pipe. When heavy rainstorms fill these pipes with stormwater, CSO outfalls release a mixture of stormwater and sewage into nearby bodies of water. The water released through a CSO outfall typically contains about 90% stormwater and 10% sewage. These relief points are needed to ensure there won’t be sewer backups into homes and businesses during heavy rainfall. CSOs and stormwater runoff have in part contributed to the complexity of cleaning up the Duwamish River. Learn more from King County here.
What cleanup progress has been made?
The members of LDWG have already invested $140 million in cleaning up 29 acres of contaminated sediment. EPA’s cleanup plan covers the remainder of the sediment cleanup actions for the 440-acre site. The cleanup is estimated to be a $668-million-dollar effort that will take time and needs to be done right. LDWG is committed to implementing the EPA’s cleanup plan as efficiently as possible. Cleanup construction of the upper reach sediment, the southernmost segment of the site, began in November 2024.
What does EAA stand for?
Early Action Areas – EAAs were some of the most contaminated sediment areas of the Lower Duwamish Waterway and presented the greatest opportunities for reducing PCB contamination in the sediment. Five of the seven EAAs identified as candidates for early cleanup have already been cleaned up. Read more here.
What steps occur before cleanup begins?
Before a final cleanup can begin, EPA and Ecology need to minimize the potential for upland sources of contamination to re-contaminate the areas that are cleaned up. EPA and Ecology are continuing to work on identifying and controlling potential upland contamination sources. Each of the LDWG members has an active role in the source control efforts.
Once the cleanup design is complete for each reach and upland sources of contamination are sufficiently controlled for that reach, the construction cleanup will proceed. A construction contractor will be selected through a bid process. For the upper reach, this process has begun, and Pacific Pile and Marine were selected to conduct upper reach sediment cleanup. That construction work began in late 2024.
What cleanup technologies will be used?
The cleanup methods in the LDW upper reach include a combination of activities. The main activities are dredging, capping, monitored natural recovery, and enhanced natural recovery. Read more about how we clean up the river here.
How long will the cleanup take?
For the purposes of the EPA Superfund Site, the Lower Duwamish Waterway is divided into three reaches, or segments: upper, middle and lower. The in-water construction in the Duwamish is restricted from October through February to protect certain fish species, such as young salmon that migrate through the river to Puget Sound. Construction of the upper reach began first, in late 2024. Middle reach construction is anticipated to begin in late 2028. Currently, the sediment cleanup for all three LDW reaches through active construction is estimated to take about 10 years. This will be followed by 10 years of natural recovery. Read more about natural recovery here. The members of LDWG will work with the EPA and project partners to minimize impacts from construction on neighbors along the Duwamish River. Learn more about construction on the Construction News page.
Where will the contaminated dredged sediment go once removed from the waterway?
For the upper reach construction, the contractor transload facility is the Duwamish Reload Facility (operated by Waste Management), located at 7400 8th Avenue South, Seattle. The dredged material is then transported by rail to a permitted landfill. The permitted landfill is the Columbia Ridge Landfill (operated by Waste Management), located at 18177 Cedar Springs Lane, Arlington, Oregon.
Who will pay for the cleanup? How much does the cleanup cost?
We are working with other responsible parties to fairly divide the cleanup costs among those who contributed to the pollution over the years. EPA has estimated the total cost to implement the cleanup will be approximately $668 million, though costs may be higher because of changes in market conditions and other factors over the next 10 years.
What happens after the construction?
After construction, LDWG will be monitoring the river’s natural recovery process. The monitoring will be conducted to determine if the cleanup is on track to meet the cleanup objectives set in EPA’s Record of Decision – i.e., it sufficiently reduces risks to human health and the environment. Because the cleanup construction is expected to take roughly 10 years, some parts of the monitoring program will begin during the construction period.