Seattle sewer lines installed in the early- to mid-20th century simply could not handle the up to 70 million gallons of polluted stormwater that flows into the Duwamish River. And as Seattle continues to grow and impervious surfaces create additional runoff, the combined sewer-wastewater systems that fill much of the Seattle area exceed the capacity of existing wastewater treatment facilities.
A $262-million project near Seattle’s Georgetown neighborhood was put in place in order to change that reality.
Pacific Pile & Marines portion of the project consisted of outfall construction which for 306 LF of 54-in OD HDPE outfall pipe into the Lower Duwamish Waterway. 106 LF of the outfall pipe is installed within a shored trench with the remaining 200 LF installed on existing grade or within a shallow burial. The final 50-ft of the outfall includes (8) 20-in duckbill valves for the diffusion of effluent into the waterway. Outfall called for precast concrete anchors bolted onto the pipe to provide weight and stability. Outfall work called for the trestle, excavation, and shoring.
