HENDERSON/ML KING CSO PROJECT: AN INNOVATIVE APPROACH TO CSO TREATMENT AND STORAGE

Reduction and elimination of combined sewer overflows (CSOs) continue to be a major focus of projects in older metropolitan areas of the United States where existing combined sewer systems convey both stormwater and wastewater. The Henderson/ML King CSO Project is one such project that will greatly reduce the number of overflows in the Rainier Beach neighborhood of Seattle, Washington. The project is one of King County's major combined sewer overflow projects, and includes over two miles of pipelines and tunnels with associated regulator structures, pump stations, and CSO treatment equipment. From the project's inception, a wide array of innovative approaches has been used to develop and complete the project including: extensive hydraulic, sedimentation, and discharge plume modeling to develop the design criteria and gain project approval from various regulatory agencies; the design of the CSO tunnel (and associated regulators) to act as a clarifier and provide both storage and treatment functions; and the use of innovative construction technologies and methods, and specific contract requirements to minimize risk and add value to the project.