The EPA’s final decision will cost the responsible parties $342 million and will cover 177 acres of the lower Duwamish River. 960,000 cubic yards of contaminated sediment will be dredged from the bottom of the river, and 24 acres will be capped with clean sediment to lock away contaminants below the surface of the riverbed.
The EPA’s final plan will cost $37 million more than the draft plan it released last year. It requires 20 percent more dredging be done. Dredging, while more costly than capping polluted areas, is widely seen as the most effective way to permanently remove pollution from waterways. It can be more disruptive in the short term because it stirs up contaminated sediment.