SEATTLE — Ten years after the U.S. Environmental Protection Agency listed the lower five miles of Seattle's only river as a Superfund site, cleanup work on some of the most toxic sections of the Duwamish River is moving forward.

On Monday, the city of Seattle will begin dredging and removing over 10,000 cubic yards of sediment in a navigational slip that is contaminated with polychlorinated biphenyls, or PCBs. The $8 million project at Slip 4 is part of a larger, decades-long effort to reduce toxic waste from a century of heavy industrial use along the waterway.

Slip 4 is one of several identified as the worst areas requiring accelerated cleanup. Another is Boeing's Plant 2, the factory that turned out B-17 bombers and was home to "Rosie the Riveter," women who built thousands of World War II planes. Earlier this month, Boeing tore down the last remaining steel structures at the plant to prepare for a large cleanup and habitat restoration project. Dredging and soil cleanup is expected to begin in 2012.

"We're at a point now where in the next several years, there's going to be a lot of progress," said David Schuchardt, the city of Seattle's Duwamish program manager. "It's very visible."

About $66 million being spent on these hotspots will reduce contamination by half, EPA officials say. The EPA is overseeing early cleanup work, which will take place over the next few years. Two sites were completed in the early 2000s.

Meanwhile, the EPA is considering options for the larger, long-term cleanup of the rest of the Duwamish that could take anywhere from four years to four decades, and cost from $220 million to $1.3 billion. The EPA will release its cleanup plan in March. A decision is expected in 2013.

The options include dredging to remove the sediment, capping it with rock and sand, or letting sediment from upriver naturally bury the toxic material, though it's likely going to be a combination of options depending on the site, said Allison Hiltner, EPA's manager for the Duwamish cleanup. Each option could potentially reduce contamination by 90 percent.

The Duwamish, once a meandering river before it was straightened and deepened into a navigation channel, runs through Seattle's industrial core and two residential neighborhoods before emptying into Elliott Bay. Decades of industrial use left behind pollution that's mixed into the mud at the river bottom and banks. Pollutants include long-lasting PCBs, dioxins, cancer-causing polycyclic aromatic hydrocarbons (PAHs) and arsenic.

Pollution from urban runoff and contaminated sites still continue to flow into the waterway, and a major concern is how to keep cleaned-up areas from getting polluted again.

"If it we get it all cleaned up, how long will it be before it gets re-contaminated?" asked Chris Wilke, executive director of Puget Soundkeeper Alliance, which conducts weekly boat patrols on the Duwamish to look for illegal pollution discharges. Pollution from sources upriver should also be addressed as part of the cleanup, he said.

The Washington Department of Ecology and EPA have been working with Seattle, King County and the port to investigate and control pollution sources.

State health officials warn against eating perch, rockfish, sole, and other resident fish, as well as crab and other shellfish from the Duwamish. Salmon are considered safer to eat because they don't spend as much time in the river.

James Rasmussen, coordinator of the Duwamish River Cleanup Coalition, which is EPA's community advisory group, said the river should be clean enough to allow people to fish freely with no risk to their health. None of the options currently do that, he says.

"To have a body of water within the city that you spend millions to clean up and source control and still not be able to eat the fish at the end of it — what have we accomplished? That's an important benchmark," he said. "We're talking about an environmental justice and health issue for the people who live there."

Lori Cohen, deputy director of the EPA's Northwest region Superfund Cleanup Office in Seattle, said "the overall goal is to reduce risk to human health and the aquatic organisms that live in the river. To what level, that hasn't been decided."

King County, the city of Seattle, the Port of Seattle and Boeing are among the potential parties responsible for cleanup. The EPA is continuing to identify others who are responsible.

Last Wednesday, on a boat tour of the waterway sponsored by the Port of Seattle, port and industry officials highlighted the river's importance to the tug companies, ship builders, manufacturing plants and cargo vessels that use it. The corridor supports about 100,000 jobs with an economic input of $13.5 billion.

"Most of the businesses really want to be clean as they can and really want to do the best, and most of are doing a very good job at it," said Everett Billingslea, vice president of Lynden Inc., the parent company of Alaska Marine Lines.

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Susan Scharff, 47, a West Seattle massage therapist on the tour, watched from the bow of the boat as a seal splashed near a tribal gillnet set out for salmon. At dusk, the river was a cacophony of noises, from metal crunching at a riverside scrapyard to squawking seagulls diving for fish.

A port "represents really enterprising, exciting aspects of cities — where things are made and things are moved," Scharff said. "The downside is that it costs us so much environmentally ... We have to clean up everything and find a way not to re-contaminate it again."