Ship Canal Water Quality Project Construction Update

The Ship Canal Water Quality Project (SCWQP) reached another milestone in December 2025 as the Tunnel Effluent Pump Station (TEPS) contract team held a topping off ceremony to celebrate the completion of the concrete shell for the aboveground pump station facility. The 65-foot-tall (20 m) cylindrical tower sits on top of a 110-foot-deep (34 m) shaft, which serves as the terminus of a new 14,000-foot-long (4,267 m) combined sewer overflow (CSO) storage tunnel. This milestone is especially meaningful for Delve Underground, as the project began in November 2015 with the start of our final design efforts. 

Once completed, the SCWQP will control the CSOs from Seattle Public Utilities’ (SPU) Ballard, Fremont, and Wallingford basins in addition to King County’s 3rd Avenue W and 11th Avenue NW basins. SCWQP is being delivered under partnership between SPU and King County to improve water quality in the Lake Washington Ship Canal. The project will reduce the volume of CSOs discharging into receiving waters by over 75 million gallons (284 million liters) each year and contribute to each agency’s long-term CSO goals. 

The TEPS contract and corresponding Ballard Conveyance project were awarded to Flatiron/Dragados in summer 2024 as part of the final phase of the major construction portion of the project. Prior to this contract, Lane Construction (Lane) was awarded the Storage Tunnel portion of the project, which included the storage tunnel, drop shafts, diversion structures, and corresponding conveyance. It also included successfully passing under the Ship Canal with a 120-inch (3 m) outside diameter, curved microtunnel drive to connect one of the drainage basins to the storage tunnel. Lane launched the tunnel boring machine from the TEPS site in 2021 and completed tunneling in 2023. Lane turned over the TEPS site to Flatiron/Dragados in fall 2024 for them to take the fit-out of the pump station to the finish line.

Over the past 10 years, Delve Underground has provided preliminary and final design services, as well as engineering services during construction, while leading a team of more than 20 consulting firms across five sites. While the technical aspects of the SCWQP are impressive, the strong relationships our team built along the way were equally important to the project’s success: relationships with our design team partners, the Owners at SPU and King County, and the construction management team and contractors carrying out this important work in the field.

The Project Team members partnered right from the project onset, and that continued through the construction periods to help foster a project-first mentality and a set of shared project goals, which were developed as part of the project charter back in early 2016. This approach helped the team remain focused on solving the problems associated with the project and keeping the project moving forward.

In addition to the typical challenges encountered during the design phase, such as limited right-of-way for construction and difficult ground conditions, the team had to adjust their typical way of doing business when the COVID pandemic hit in early 2020, just as the Storage Tunnel Contract was getting underway. This was one of the greatest challenges and underscored the importance of the relationships built during the design period, as that trust helped everyone successfully transition into this new way of doing business.

With the TEPS construction expected to be completed by the end of 2027, we are nearing the tail end of the project. While the technical achievements are impressive, the relationships built along the way will continue to make the difference as we continue to support this important work to clean up our local waterways. Congratulations to the entire team, and a well-deserved shout-out to Flatiron/Dragados for recently surpassing 100,000 work hours without a lost-time incident, demonstrating a shared commitment to safety and collaboration.