King County, WA, Completes Challenging Sewer Bypass and Rehab of Eastside Interceptor

King County’s Eastside Interceptor (ESI) collects the majority of waste¬water flows from the Puget Sound Area Cities of Kirkland, Bellevue, Mercer Island, Sammamish, Issaquah, Newcastle and Renton, and conveys it to the County’s South Treatment Plant. This aging reinforced concrete pipe (RCP) inter-ceptor was constructed over 50 years ago and corrosion caused by hydrogen sulfide (H2S) gas has begun to take its toll on the pipe’s interior.

Sections of the pipe are experiencing mild to severe corrosion that causes the concrete interior to crumble, exposing rebar and affecting the structural integrity of the pipe. The County has developed a proactive approach to deal with the degra¬dation of the pipe by identifying sections of pipe experiencing corrosion, prioritizing rehabilitation needs based on severity, and developing projects to carry out the reha¬bilitations to keep the line in service.

The Eastside Interceptor Section 2 (ESI2) Rehabilitation Phase II Project was developed to rehabilitate approximately 3,700 ft of a severely corroded 96-in. diameter section of the ESI intercep¬tor line located in Renton. The project is funded through King County Wastewater Treatment Division’s Capital Improve¬ment Program which uses proceeds from revenue bond sales, short-term borrowing, and capacity charge revenues from sur¬rounding cities. This section of pipe runs through an urban area between Boeing’s 737 commercial airline facility and the Renton Landing, a busy mixed-use devel-opment. Beginning in 2016, King County performed an alternatives analysis that looked at various rehabilitation options for the Project including cured-in-place pipe (CIPP), spiral wound PVC liner, and Lina¬bond. Linabond was selected as the most appropriate rehabilitation method for this section of pipe as it maintained the great¬est existing capacity. Carollo Engineers, Inc. was contracted by the County in the summer of 2018 to complete the prelimi¬nary design effort and prepare the design in the hopes of constructing the project in the 2019 dry season. This required a fast-track approach to design, permitting, and easement acquisition.