The Superfund site in the lower Duwamish River is a 5.5-mile stretch contaminated with toxic chemicals from storm water pipes, city runoff and years of heavy industrial use.
After studying riverbed sediments in the lower Duwamish, the EPA discovered more than 42 chemicals, including polychlorinated biphenyls (PCBs), pesticides, arsenic, dioxins, furans, oil and other hydrocarbons and heavy metals like mercury and lead.
A long-term cleanup plan for the entire affected area of the river is in the works. But the EPA determined that some segments may become a threat to people or the environment before cleanup is complete and suggested immediate action.
The city answered by investing millions to clean up a four-acre area – called Slip 4 – that was identified as one of the most toxic stretches of the river.
On Monday, city workers began the process of dredging and removing more than 10,000 cubic yards of sediment that is contaminated with PCBs, according to an article published on Sunday by The Seattle Post-Intelligencer.
The $8 million project at Slip 4 is the start of what could be a decades-long cleanup project on the lower Duwamish, the EPA said.
The city has already successfully cleaned up portions of the east side of the river that were found to be contaminated with combined sewage overflow from storm drains. More than 70,000 cubic yards of contaminated sediments were removed in the Norfolk Area and Duwamish/Diagonal Site projects.
Boeing’s Plant 2, the factory that once produced B-17 bombers and thousands of World War II planes, has also been identified as a particularly toxic site on the Duwamish.
At the end of September, Boeing tore down the last remaining steel structures at the plant to make way for site restoration, which includes excavating more than 200,000 cubic yards of sediment and restoring about a half-mile of natural habitat along the shoreline. Dredging and soil cleanup is expected to begin next year.
A site known as Terminal 117, located on the west bank of the lower Duwamish in the South Park neighborhood, has also been identified for early action. The site, which was used to produce asphalt in the 1930s, was found to be contaminated with oil and other hydrocarbons.
Interim cleanups have removed much of the soil contamination and a final cleanup is scheduled to begin between 2012 and 2014, according to the Lower Duwamish Waterway Group.
About $66 million being spent on these sites will reduce contamination by half, EPA officials told the Post-Intelligencer.
The EPA and the Washington State Department of Ecology (Ecology) are overseeing cleanup in these “early action” areas while working on long-term plans to restore the entire river.
After years of research, EPA and Ecology have released a fact sheet and the first draft of a Feasibility Study to plan for cleanup. The EPA will release a final cleanup plan in March and a decision is expected to be reached by 2013, the Post-Intelligencer reports.
Options included in the early Feasibility Study include dredging to remove sediment, capping with rock and sand or letting sediment from upriver naturally bury the toxic material. Each option could potentially reduce contamination by 90 percent, the EPA said.