Portage Bay 138 Gate Retrofit & Pump Station 20 Improvement Project

Photo of Portage Bay from street end of E Shelby St.
This project will improve water quality in Portage Bay.

Project Description

Portage Bay 138 is a combined sewer basin, where combined sewage and stormwater flows to Pump Station 20 located at the street end of E Shelby St and is then pumped through sewer pipes to a treatment plant. Rain and other factors can increase flows through the basin, and SPU can manage this by temporarily diverting increased flows to belowground storage pipes along the street end of E Shelby St and then slowly releasing flows back into the system.
However, during heavy rain events, high volumes of stormwater could overwhelm the sewer system and cause a combined sewage overflow (CSO) into Portage Bay via an underwater outfall pipe. The combined mixture of raw sewage and polluted stormwater can be harmful to humans, aquatic life, and other wildlife.

For this project, Seattle Public Utilities (SPU) modernized the way our existing infrastructure manages high flows during rainstorms to reduce the occurrence of CSOs. SPU automated the process for diverting flows to the temporary storage pipes, which allows SPU to optimally manage flows in real time.

SPU also made improvements to Pump Station 20, which is located at the street end of E Shelby St. This work helps SPU maintain reliable services by reducing the risk of pump station failure, maintaining safe working conditions for SPU crews, and helping SPU comply with safety standards and industry regulations.


Construction took place at the street end of E Shelby Street near Fuhrman Ave E and Boyer Ave E.

Project Results

SPU performed this work to enhance the functionality of the infrastructure and to improve SPU's ability to manage flows more efficiently. In addition, this project improved water quality and public health in the region by reducing the number of CSOs into Portage Bay while upgrading our infrastructure to enhance service reliability


Construction began in early 2020 and was completed in December 2020.

Related Information

SPU works to maintain, build, and manage Seattle's sewer system to protect our city and the environment from overflows and backups. Learn more about how SPU works to prevent sewer overflows.

Public Utilities

Andrew Lee, General Manager and CEO
Address: 700 5th Avenue, Suite 4900, Seattle, WA, 98104
Mailing Address: PO Box 34018, Seattle, WA, 98124-5177
Phone: (206) 684-3000

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Seattle Public Utilities (SPU) is comprised of three major direct-service providing utilities: the Water Utility, the Drainage and Wastewater Utility, and the Solid Waste Utility.