Thea Foss Waterway Cleanup
Tacoma’s Thea Foss and Wheeler-Osgood waterways shine with restored vitality, thanks to a historic cleanup led by the City of Tacoma.
Over a century of industrial practices left sediments heavily contaminated, but through collaboration with various agencies, organizations, property owners, and other responsible parties, the City took action to remove or cap these pollutants, transforming the marine habitats around the waterway.
Since the project’s completion in 2006, maintaining a clean waterway remains a top priority. You can read our current Stormwater Source Control Report here.
Turning the Tide
Learn More About This Historic Project
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In 1983, the EPA designated the Thea Foss and Wheeler-Osgood waterways as part of the 12-acre Commencement Bay Superfund site. This area had long been a hub of industry due to its prime waterfront location and proximity to the Northern Pacific Railroad. Early practices led industries to discharge waste directly into the water and sewer systems that emptied into the bay, resulting in over one million cubic yards of contaminated sediment.
The following contaminants were detected:
- Phthalates: Common in PVC products, detergents, and solvents
- Petroleum-based products: From incomplete burning of coal, oil, and gas
- Polychlorinated Biphenyls (PCBs): Used in electrical equipment
- Phenols: Found in adhesives, construction, and automotive products
- Metals: Arsenic, copper, lead, mercury, and zinc
- Pesticides: Including DDT, DDD, and DDE
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In 1994, Tacoma stepped forward to lead the cleanup, conducting extensive investigations to map and measure contamination levels. After assessing multiple options, the City launched a comprehensive cleanup covering 80% of the Thea Foss Waterway, while Puget Sound Energy and PacifiCorp handled the remaining 20%.
Between 2002 and 2006, over 425,000 cubic yards of contaminated sediment were dredged, transported to containment areas, or capped with clean sediment. Alongside the dredging efforts, several shoreline areas were transformed into habitat-friendly spaces, including the Middle Waterway Tideflats Habitat and North Beach Habitat.
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To sustain these efforts, the City created an Institutional Controls Plan to prevent further contamination. Key measures include:
- Landowner agreements to safeguard shoreline areas
- Rigorous standards for new construction near capped zones
- Regular monitoring by the City and the Department of Ecology
Stormwater management remains a focus, with runoff from over 6,000 acres flowing untreated to the waterways. Efforts to control this pollution include inspections, storm drain maintenance, and public education. Annual monitoring reports, such as the Thea Foss Operations, Maintenance and Monitoring Plan (OMMP), track water quality, sediment, and habitat integrity.
You can find additional monitoring reports below.