Improving Water Quality in Northwest Seattle

During heavy rain events, Seattle’s network of pipes are designed to release combined sewage overflow into the surrounding waterbodies via several outfalls to protect buildings and roadways from overflows. Currently, CSOs from Ballard, Fremont, Wallingford and Queen Anne overflow into local waterways 104 times per year on average. This project will limit those overflows to less than one overflow per outfall per year on average and keep an average of more than 75 million gallons of raw sewage and polluted stormwater out of our local waterways.

When fully implemented, the Ship Canal Water Quality Project, a joint project between Seattle Public Utilities and King County, is designed to reduce the frequency of CSO events to 1 per year at each of its outfall locations, based on a 20-year moving average. A new 2.7-mile storage tunnel will temporally store 29 million gallons of CSO during these heavy rain events.

We are the lead designer of the pump station that drains the storage tunnel after use. The pump station is located at the Ballard site and is the main above-grade feature of the Project. The goals for the Ballard site are:

• Express function locally and citywide
• Derive benefits for Seattle community and SPU
• Contribute to and recognize the place and role of waterfront in Ballard
• Connect the neighborhood to the waterfront

The site lies in an industrial area, near the Ship Canal and the Ballard business district. Our team has responded to Seattle Design Commission recommendations, in particular how various design elements were integrated into one cohesive design concept.

Design Goals Minimize Footprint of Pump Station

As part of the overall project, the pump station includes an above-ground structure that is approximately 65 feet high and an underground structure that is approximately 100 feet deep. The underground structure connects to the storage tunnel and houses the pump station equipment. The station will pump stored CSO from the tunnel, and it will be conveyed to King County’s West Point Treatment Plant.

The pump station’s current design aims to provide a fully functional and well-integrated design while not preempting future development. The design goals include minimizing the footprint of the proposed pump station while reconnecting the neighborhood with the waterfront.

Equity was addressed in outreach, contracting and the art of the project.

HDR’s work includes:

• Building a station to pump polluted water out of the storage tunnel for treatment
• Providing pumps, odor control, HVAC, and electrical equipment, and a 65-foot above-ground building
• Installing conveyance piping near the Ballard site to divert flows for storage to the underground tunnel and to convey pumped flow to treatment
• Providing landscaping, fencing and maintenance areas
• Coordinating the design for temporary artwork along the fencing and permanent art to reflect the Coast Salish culture. The proposed artwork draws on the maritime industrial and indigenous histories of the site, including inspiration from Calypso, Jacque Cousteau’s ship, which was built just west of the site.

Envision Verification

For the entire Ship Canal Water Quality Project, our team helped to improve project sustainability by facilitating the application of the Envision® framework. Sustainable elements include modeling tunnel sizing to improve resiliency and longevity, using phytoremediation and green stormwater infrastructure at the Ballard site, incorporating a temporary urban tree farm and working with other organizations to improve safety, mobility and access.