Cleaning the Duwamish
The Duwamish is the only river that still flows through Seattle. The lower five miles, between the southern tip of Harbor Island and the Turning Basin, have served industry for the past century. The original Boeing airplane plant was there, followed by four other major Boeing facilities. Industries along the Lower Duwamish included steel mills, cement plants, shipbuilding and repair, and more. Stormwater, sewage, and industrial wastewater flowed into the waterway for many years, resulting in polluted river-bottom sediment.
The pollutant that causes the greatest risk to people are the PCBs - polychlorinated biphenyls. They cause cancer and can harm neurological and reproductive systems, as well as causing other ailments.
The developer of PCBs, Monsanto, began manufacturing PCBs in the 1930s and marketed them for use in a wide variety of products, including as an insulating fluid for electrical equipment, and as an additive to exterior paint and caulk. These two products in particular – exterior paint and caulk – still exist today on buildings near the Lower Duwamish. Over time, PCBs leave the paint and caulk and are washed by rain into stormwater that goes into the City’s drainage system. Eventually that stormwater flows to the Lower Duwamish, which begins an extremely dangerous cycle of introducing PCBs into the food chain.
PCBs, which last virtually forever, make their way into the bodies of aquatic life residing in the Duwamish sediment. These species, then, are consumed by predators which are in turn – as a natural course of nature – consumed by their predators. Each time this occurs, PCBs become more concentrated. People who catch and eat fish and shellfish residing in the Lower Duwamish are introducing PCBs into their bodies at unsafe levels. That is why the Washington Department of Health has issued advisories warning people not to eat any resident fish or shellfish from the Lower Duwamish. (Salmon swim through the waterway fairly quickly, therefore the advisory does not include them.)
In 2016, the City of Seattle sued Monsanto. The City’s position was straightforward: that Monsanto’s production and promotion of PCBs contaminated the Lower Duwamish Waterway and the surrounding drainage area. In July 2024, after eight years of litigation, Seattle City Attorney Ann Davison negotiated with Monsanto, which agreed to pay the City of Seattle $160 million to release the City’s claims. This amount is larger than any previous settlement paid by Monsanto to a local governmental entity.
Working to have the Monsanto company contribute significantly is not the only strategic step the City of Seattle has taken toward restoration of the Lower Duwamish. A first step was taken in 2000, when the City began actively investigating contamination in the Lower Duwamish and the surrounding drainage area. The City, King County, the Boeing Company, and the Port of Seattle all signed on as part of a voluntary effort to clean the Duwamish. This effort is governed by a joint administrative order from the Environmental Protection Agency and the Washington Department of Ecology.
Since then, the City has participated in cleaning four parts of the river that contained particularly high levels of PCBs. In September 2024, work will begin on the rest of the waterway, with the participation of the City of Seattle, King County, and Boeing. This work involves dredging and removing the most contaminated sediment, capping other contaminated areas with clean material, and monitoring areas that are expected to become buried under cleaner sediment coming from the Green River.
Getting the Lower Duwamish clean enough for people to eat the resident fish and shellfish will require reducing the continuous flow of PCBs into the river, both in the areas adjacent to the cleanup and in upriver areas. With the Monsanto settlement funds, the City can take some of the steps that are necessary, including stormwater treatment and expanding the City’s source control program to identify buildings where PCBs remain in exterior paint and caulk.