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Walnut Creek, Calif. — Honolulu Mayor Kirk Caldwell announced completion of Hawaii’s “largest-ever” wastewater system upgrade. Following a U.S. Environmental Protection Agency Consent Decree to improve Windward Oahu’s sewage collection and treatment system by June 2018, Brown and Caldwell worked with the City and County of Honolulu and its team of construction partners to deliver the Kaneohe-Kailua Wastewater Conveyance and Treatment Facilities Project on an accelerated schedule and within budget.

The solution involved connecting the Kaneohe Wastewater Pre-Treatment Facility (KWWPTF) to the Kailua Regional Wastewater Treatment Plant (KRWWTP) via a three-mile long, 10-foot-diameter gravity sewer tunnel, increasing the region’s wastewater conveyance and storage capacity while reducing overflows. The tunnel conveys wastewater by gravity flow, sloping from a depth of 39 feet below ground level at the KWWPTF down toward the KRWWTP, ending at 77 feet below ground level. Traveling under Oneawa Hills was the preferred tunnel route, rather than placing a force main through Kaneohe Bay, therefore avoiding potential catastrophic sewage overflows into the environmentally sensitive public resource.

To lift the wastewater to the surface for treatment, a 45 million-gallons-per-day (mgd) Tunnel Influent Pump Station was designed by Brown and Caldwell and constructed at the KRWWTP. The project also includes a new 15 mgd replacement for the existing Kailua Influent Pump Station, generator and headworks buildings, and odor control facilities.

“This first-of-its-kind project in Hawaii is one the entire community can be proud of,” said Honolulu Mayor Kirk Caldwell. “Our team has created a world-class sanitation facility that will last for generations, while also protecting the environment that’s so important to our island lifestyle.”

A significant benefit of the project is reduced energy consumption paired with improved environmental protection. Wastewater conveyance via the new tunnel system occurs through gravity flow rather than pressure, eliminating three upstream pump stations and a three-mile long force main, all considered potential community overflow points.

“Our goal was to help the city construct and deliver an important asset to protect community health and wellbeing while not adversely affecting the environment,” said Brown and Caldwell Pacific Area Leader Ray Matasci. “I feel privileged to be part of an engineered solution that protects and sustains Hawaii’s cherished landscape.”

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