King County turns to new contracting method to fix critical wastewater pipes 

Repair of the Eastside Interceptor tunnel requires a complete diversion of wastewater flow through a bypass to keep the system working during construction. One possible setup is represented in the photo.  

Imagine deciding to bake a cake without any idea of the recipe. You begin, only to discover that you need to go shopping for missing ingredients. Or you have to add extra flour because the batter is too thin. Or the bake time runs an extra 15 minutes over.  When you’re finally done … that cake project has taken more time and money than you expected.   

Large construction projects can be sort of like that cake project. Traditionally, public projects are designed under one contract, and built under another. By the time construction crews start the work, design meets reality – often in the form of costly unexpected change orders to the project and delays.   

King County Wastewater Treatment Division (WTD) has project needs so critical it can’t afford such uncertainties. Two major wastewater pipe systems – one in Bellevue and one in Auburn – are corroded after more than 50 years of use and need repair and replacement. Both projects must be done during compressed time windows.   

“There is no extra bake time,” said Lisa Taylor, WTD’s capital project manager. “We had to think creatively and strategically about how we were going to get these projects done on time and at cost.”   

So, King County submitted the case for an alternative method of project delivery called “progressive design build.” This contracting method brings designers and builders to the same table at the early stages of project development. The private sector often uses progressive design build, and it has been gaining interest in the public sector as well. King County built Brightwater Treatment Plant in Woodinville in 2011 using progressive design build, adding substantial capacity and cutting-edge technology for wastewater treatment.   

“We know progressive design build will save time, employee resources, and ratepayer dollars for these projects,” said Taylor. “We hope this will usher in a new era of efficient contracting for our capital and asset management programs.” 

With approval from the Washington State Capital Projects Advisory Review Board, WTD will soon solicit Requests for Qualifications (RFQ) for the two projects.   

In Bellevue, a mile-long portion of the approximately 8-ft diameter Eastside Interceptor pipe – one of the main wastewater lines connecting Eastside cities to the South Treatment Plant in Renton – will be re-lined to ensure that the tunnel can withstand decades more of use. Shutting off the line during repairs is not an option, so a robust diversion pumping system large enough to carry 55 million gallons per day must be installed to allow for the rehabilitation of the tunnel during the short dry season.  

Meanwhile, in Auburn, the “M Street Trunk” project will fix a concrete pipe and dozens of maintenance holes between Auburn Municipal Airport and state Route 18. The work shuts down a major roadway, so the construction crews have to get in and out of there as efficiently as possible to minimize community impacts.  

The contracts will require priority hire, apprenticeship and Disadvantaged Business Enterprise and Minority and Woman Owned Business participation goals. Both projects are expected to be substantially complete by December 2025.  

A section of the East Side Interceptor pipe in Bellevue shows signs of heavy corrosion from hydrogen sulphide, which forms inside pipes especially when wastewater is stagnant. This is a common problem in older pipes that have endured decades of use. WTD teams monitor pipes and identify ones in need of replacement. WTD maintains and upgrades King County’s aging wastewater infrastructure so that it can perform well into the future. 
The Eastside Interceptor pipe  – one of the main wastewater lines connecting Bellevue and Eastside cities to the South Treatment Plant in Renton – will be re-lined (similar to photo shown) to ensure that the tunnel can withstand decades of further use

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