The largest of all Portland’s projects to reduce overflows into the Willamette River, this tunnel is designed to significantly reduce sewage and storm water overflows.

The East Side CSO (“Big Pipe”) Project will extend for approximately 6 miles from the vicinity of 17th Ave. and McLoughlin Blvd., proceeding north along the east bank of the Willamette River, and connecting to the West Side CSO facility on Swan Island.
Work will include excavation and lining of an approximately 22-ft. dia. tunnel constructed 85 to 165 ft., below ground and seven separate shafts located along the alignment. Ultimately, the East Side CSO will collect and intercept overflows from 12 existing combined sewer outfalls that discharge to the Willamette River.

Other principle features of the project include connecting pipelines and diversion structures to direct overflow from the existing collection system to the CSO tunnel.

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