University CSO GSI Design Project

King County is actively working to prevent heavy rains from causing combined sewer overflows (CSOs) into Portage Bay in Lake Washington. Herrera supported the County in evaluating alternatives for green stormwater infrastructure (GSI) in the University CSO basin with the goal to reduce the required size of a downstream storage facility and maximize benefits to the community. The large scale of this project (over 1,100 blocks), and the wide variety of GSI practices in our toolbox, posed a unique challenge to efficiently identify the best combinations of project sites and GSI practices. To this end, Herrera leveraged their GSI Cost Performance Tool, developed under a separate contract for the County, to evaluate the cost and benefits of each block and GSI combination.