Seattle Public Utilities

Swale on Yale – Capitol Hill Water Quality


Phase 1 of the Swale on Yale project was completed in 2013.


Whenever it rains, untreated stormwater from more than 630 acres of Capitol Hill drains directly into Lake Union via the Minor Avenue outfall. Currently, stormwater flows across the streets of upper Capitol Hill, collecting silts, oils, heavy metals, and other pollutants before being piped downhill, under the Cascade neighborhood, and into the lake.

SPU has prioritized treatment of stormwater discharges from the Capitol Hill Basin and we feel this is a prime location to retrofit the stormwater system with cost-effective treatment.

Main factors contributing to this project

  • Cascade neighborhood is experiencing significant development.
  • Location of the biofiltration swales allows for gravity flow from the Capitol Hill storm drains to the swales and back into the storm drains.
  • Capitol Hill stormwater flows have a higher concentration of stormwater pollutants than typical residential neighborhoods.


Total cost of this project is approximately $11 million. SPU has received a $1 million stormwater grant from the Washington State Department of Ecology’s FY2011 Stormwater Retrofit and LID Competitive Grant Program and a $1.8 million loan from the Washington State Water Pollution Control Revolving Fund Loan Program.

SPU is actively working with Vulcan, Inc., a local Cascade Neighborhood Partner, in developing and funding the Swale on Yale. They have provided technical and professional services and will be funding $1.2 million of the design and construction costs of the project.


Jason Sharpley, project manager
(206) 615-0030

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