The Henderson - M.L.King CSO project is managed by the King County Department of Natural Resources, working in concert with City of Seattle Public Utilities. The sewer system in the Rainier Beach area was 50 years old and in need of improvement. This $45 million sewer construction project improved water quality and protected Lake Washington from combined sewer overflows (CSOs) during extreme storms. The work added capacity and improved the system’s efficiency to convey, store, and treat both waste and storm water.

Tetra Tech INCA provided construction survey services for the location and grading of the 20 “ forcemains, 42”, and 72” pipelines, bridge construction, Regulator and Inlet sites, and control for the construction of the 14 foot storage tunnel. There was also an extensive surface monitoring program that INCA provided the locations for placement and continuing survey measurements of those points during construction of both the pipeline and tunnel portions. There were several street and site improvements that were surveyed. INCA also provided a topographic map of Henderson Street, from Yukon Avenue South to Seward Park Avenue South, for the City of Seattle’s use in the design of street improvements.

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