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Working with Sammamish Plateau: No regional capacity limits and Diversion Project moving ahead

By January 20, 2021September 27th, 2021No Comments

We clean wastewater for the region

Pipes from homes and businesses in this area connect to local sewer systems. Then those local utility pipes connect to our bigger pipes, which carry wastewater to one of our regional treatment plants where we clean it.

The local agencies own and operate their independent collection systems. The local agencies have contracts with us that legally require us to accept their wastewater flows and treat it.

Lake Sammamish
Lake Sammamish

Working with Sammamish Plateau Water

One of the local utilities we have a sewage disposal contract with is Sammamish Plateau Water. That contract requires us to provide enough sewer capacity in our regional sewer pipes to carry and clean all wastewater flows from the District’s service area. Currently, there are no limitations on the amount of flow our system can accept from the Sammamish Plateau system.

Diversion Project moving ahead

We are planning a construction project known as the Sammamish Plateau Northern Diversion Project (Diversion Project) that would shift a portion of flows from Sammamish Plateau’s system north to our Brightwater Treatment Plant. This project would add even more capacity to our pipes for us to serve future demand.

Sammamish Plateau Water has told us that this project will also help them with capacity constraints they have identified in their local sewer system.

The project was deferred in 2018, which moved the completion date for the project from 2028 to 2030. Sammamish Plateau Water has known since 2016 that it is a 10-year project. The King County Executive has committed to propose full funding for the project in the County’s 2023-2024 biennial transmittal to Council.

We will build additional capacity in time to serve growth when it occurs

We are also working with Sammamish Plateau Water to help address capacity constraints in their local sewer system. Specifically, we funded a study completed in January 2021 to identify which interim projects could be constructed to bridge the gap until the Diversion Project is completed.

Sammamish Plateau Water has also requested that we purchase a portion of their system. We are evaluating their request.

We will work with the district to make local system improvements if needed.

We take our responsibility to treat wastewater seriously because it protects public health and the environment. We will continue to meet our obligations under our sewer contracts.

Update: The Sammamish Plateau Water (SPW) sewer moratorium has expired. SPW accepted King County’s offer to pay 50 percent of identified upgrades/repairs. SPW and King County are finalizing a cost-share agreement that includes King County paying for $5.927 million in interim improvements to SPW’s sewer system.

Marie Fiore, 206-263-0284 or