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Project update

July 2018

While construction of the full project is planned for 2021 to 2023, King County is also planning one or more early action projects. King County’s work studying soils in July will further the assessment of locations for potential installations of green stormwater infrastructure on the right-of-way (also known as planting strips). The County plans construction of early action projects for 2019.

The project team knows that residents may have many questions about green stormwater infrastructure and what it means for their street. Should construction be planned, King County will work with the community to provide project information and identify potential impacts. Stay up to date by visiting this web page, by signing up for the project email list, and by using the contact information here to check in with us with any comments or questions.

For more information, view the updates:

View past updates on the project library page.

Project description

King County is beginning a green stormwater infrastructure project in north Seattle. This project will install facilities to help control a combined sewer overflow in Portage Bay. In 2017-18, the project team will study soil, groundwater, surface water flow, and street conditions in the project area to identify the best locations for facilities to be installed.

In this first phase of the project the County will consider what types of green stormwater infrastructure it should build, and where within the study area they should be installed. Some options include different types of bioretention and permeable pavement in alleys or streets. Learn more!

Project study area

The project will select sites for installing green stormwater infrastructure from within the area below.

Study area is near Green Lake, Seattle  Click to view more of map .

Approximate boundaries are intended for planning purposes only. Further study and evaluation will be completed prior to selection of any site.

Project need

In the University CSO Basin in Seattle, heavy rains can cause sewers to overflow into Portage Bay approximately six times per year. This project will install facilities to help control these overflows. Learn more about King County’s CSOs.

What is green stormwater infrastructure?

Green stormwater infrastructure—also called natural drainage—mimics nature by slowing or reducing polluted runoff close to its source. It also treats polluted runoff from roads, roofs, and parking lots by capturing and cleaning it before it harms our waterways. Learn more!

Your feedback 

The County will share its evaluation of two to four alternative ways of doing green stormwater infrastructure with the public, and ask for your feedback online and through community events. Visit the public involvement page.

Project schedule

4Q 2017 Alternative analysis begins

Early action project schedule

While construction for this GSI project will take place in 2021-23 (see left), the County plans to install early action projects in 2019.

1Q 2019 Alternative analysis complete
3Q 2019 Predesign complete
1Q 2021 Final design complete
2Q 2021 – 2Q 2023 Implementation (bidding, award, construction)


Contact us

Contact Dana West, Community Services, at:

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Green stormwater infrastructure installed at a Roosevelt neighborhood church:

The County’s green stormwater infrastructure project in West Seattle:

The big picture:

RainWise rebates:

  • Many residents of this area can install their own green stormwater infrastructure (rain gardens and cisterns) on their own property funded by an average $4,400 rebate. Check your eligibility and learn more .

houseThe County will consider installing different types of green stormwater infrastructure in the public right-of-way, including types of bioretention in planting strips and permeable pavement in alleys or streets.