West Side CSO Tunnel

It receives and stores overflow from the combined sewer system before it can reach the Willamette River.

Portland's 1930s sewer design combined street and surface runoff with sewage in a common system that was overwhelmed during heavy precipitation.

[2] The Clay Street shaft receives the Southwest Parallel Interceptor, a 3-to-6-foot (0.91 to 1.83 m) pipeline which runs along the west Willamette shore for 3 miles (4.8 km) to Virginia Avenue and Taylors Ferry Road 45°28′13″N 122°40′21″W / 45.47015°N 122.67240°W / 45.47015; -122.67240 (SW Parallel Interceptor south end).

[3] The project is a part of the Willamette River combined sewer overflow expansion program.

[5] The total cost of the projects, about $1.4 billion, is being financed over time through additions to the Portland sewer rates.