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Learn about how we study soil conditions in your area

One type of green stormwater infrastructure that the project is evaluating for this area is bioretention in the planting (parking) strip. The County does testing to evaluate soil and groundwater conditions. This will help us understand how well stormwater soaks into the ground.

The need to control Combined Sewer Overflows (CSOs)

King County's University CSO Basin

1801_Univ-GSI-CSO-Map-rev_600In the University CSO Basin , heavy rains can cause sewers to overflow into Portage Bay and the Lake Washington Ship Canal.

As in many cities around the country, the older parts of King County’s sewer system use the same pipes to carry both sewage and stormwater to a treatment plant. During storms, sewer pipes that carry stormwater can fill up with the stormwater that runs off roofs, driveways and streets. When the pipes fill up, the sewer system can be overwhelmed. The system is designed to allow these overflows (a combination of 90 percent stormwater and 10 percent sewage) into local water bodies. We call this a combined sewer overflow, or CSO. Even though these CSOs help prevent back-ups into homes and businesses, they pose a risk to public health and the environment.

More about green stormwater infrastructure

Unlike the use of pipes, underground storage tanks, and treatment plants that collect and clean stormwater - green stormwater infrastructure uses natural processes like rain gardens and cisterns to slow, capture, and clean polluted runoff before it harms our lakes, rivers, and streams. It also helps add color and beauty to our homes and communities.  

By installing green stormwater infrastructure in our public spaces, King County can help reduce pollution entering waterbodies, reduce the need for large, industrial water treatment and storage facilities, and add greenery and beauty to our neighborhoods. Cities around the country are increasingly turning to “green” infrastructure as an effective way to control stormwater and reduce pollution. View resources to learn more.

More about the University Green Stormwater Infrastructure Project

The project would have three major phases: alternatives analysis, design, and construction.

In this “alternatives analysis” phase the project would compare different options for doing green stormwater infrastructure in terms of cost-effectiveness, community impacts, and sustainability. By the end of this process, the County would have chosen an option or options to install and would work out how much green stormwater infrastructure can be built in the basin.

While the green stormwater infrastructure would control some of the basin’s stormwater, the County also plans to build large storage tanks or tunnels, or wet weather treatment facilities near the Ship Canal to prevent CSOs. View resources to learn more.

Public input

The County would share its technical evaluation of the green stormwater infrastructure solutions with the public, and ask for feedback. Based on the technical evaluation and community feedback, the County would adjust the plans to create the best alternative(s). That choice would help determine the project’s design and construction of GSI in the Project Area. This thorough process ensures that the green stormwater infrastructure installed would meet the needs of controlling stormwater by reducing combined sewer overflows and the needs of the community. View the public involvement page.


Contact us

Contact Dana West, Community Services, at: