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Green, Clean Bridges & Elevated Highways

Photo: Hannah Letinich

Private-Public Partnership Cleans Over Two Million Gallons of Stormwater Annually 

Seattle Hotspot for Contaminated Stormwater

It’s another rainy day in Seattle. In the city’s Fremont neighborhood, stormwater flows off the Aurora Bridge, which spans the Ship Canal, connecting Lake Union to Puget Sound. The stormwater, which fell as rain, is now laden with toxic chemicals and metals from rubber tires, brakes, motor oils, antifreeze and other sources. It’s so polluted that national stormwater expert, Dr. Richard Horner, found the Aurora Bridge creates the most-contaminated runoff he’s ever tested.

Every year, a million gallons of this stormwater rolls off the Aurora Bridge into the waterway below—where it contaminates a key route for migrating salmon and eventually flows into Puget Sound.  In urban waters like Lake Union, stormwater may kill up to 80 percent of migrating Coho salmon before they have a chance to spawn. The beloved Southern Resident Orcas are endangered too, in part due to high levels of stormwater toxins affecting their immune systems and reproductive rates.

A Private and Public Partnership Solution

Developer Mark Grey of Stephen C. Grey & Associates and founder of the non-profit Clean Lake Union, and his partners Mike Hess and Joanna Callahan, were just beginning work on a new office building in Fremont when Grey saw a short video called “Solving Stormwater”. The video explained the devastating effect untreated stormwater has on salmon, and the potential solution – green stormwater infrastructure. With the proposed building located directly beneath the Aurora Bridge, he realized they were in a unique position to make a difference.

 As part of their proposed building design, the partners in conjunction with Clean Lake Union, began engineering bioswale retention systems and rain garden landscaping to capture and clean the polluted stormwater from the north end of the bridge. During this process they teamed up with Salmon Safe and The Nature Conservancy, convening multiple organizations to help make the project a reality. The project’s three phases will clean over two million gallons of stormwater annually. 

Honored with the King County Green Globe award, the Aurora Bridge bioswale project is the result of private and public partners coming together to solve this daunting challenge with a pioneering approach, despite the complex collaboration and steep regulatory requirements.

Read more about the Aurora Bridge Bioswale project here

Unprecedented Collaboration and Impact

The Aurora Bridge project will treat over two million gallons of heavily polluted runoff annually to high standards of water quality that is safe for salmon habitat. The project impact goes beyond clean water with additional lasting benefits:

  • Unprecedented private-public partnership. Provides a powerful example of collaboration between private businesses and government, and the commitment required, to implement groundbreaking models for green infrastructure.
  • Trail blazing the regulatory process. Landing at the intersection of transportation, surface-water runoff, green infrastructure, and building design, the project blazes the permitting and regulatory trail, easing efforts for future projects.
  • Good for people and business. Bioswale landscaping brings inviting green space to the Fremont neighborhood, creating an attractive setting for nearby employees and residents.
  • Inspiring future green infrastructure. Building on the success of the project, a study has investigated similar strategies for the south span of the Aurora Bridge and five other bridges that cross Lake Union.


What’s a Bioswale?

Bioswales offer a natural filtration solution that greatly reduces pollutants entering waterways. These natural landscape elements are engineered to concentrate debris and remove pollutants from stormwater runoff before it drains into local waterways.

Adobe Inc.
The Boeing Company
City of Seattle
Clean Lake Union
Clean Washington Waters
Fremont Dock Company
HAL Real Estate
Hess Callahan Partners
Salmon Safe
Spear Street Capital
Stephen C. Grey & Associates
Tableau Software
The Nature Conservancy
Turner Construction Company
Washington State Department of Commerce
Weber Thompson