Black Diamond wastewater infrastructure upgrade

As part of its mission to protect public health and the environment, King County is responsible for conveying and treating wastewater collected by 34 local city and sewer agencies in the King County region. Wastewater from Black Diamond homes and businesses is collected by the City of Black Diamond's local sewer system and then transported to King County's South Treatment Plant in Renton through a network of conveyance pipelines and pump stations operated by the county and the Soos Creek Water & Sewer District (external link).

Growth in Black Diamond is projected to reach approximately 20,000 residents by 2025. As the city's wastewater conveyance and treatment provider, King County must build additional wastewater capacity in Black Diamond to accommodate the projected growth.

The City of Black Diamond and King County are working together on plans to build new wastewater management facilities that will provide additional capacity in two phases. The capital and operating costs for these new facilities will come from revenues generated by sewer rates and hook up charges for new development.

King County is adding wastewater capacity in Black Diamond to accommodate projected population increases in the city's master planned areas. The city’s master-plan development has slowed down significantly. As a result, this project is on hold until a schedule detailing when actual development permits will be issued and construction will occur for the master-planned areas of Black Diamond becomes available from the city. At that time, the county will work with the city to determine when the Black Diamond Storage Facility project is needed to meet the city’s wastewater capacity needs.