McMillen Jacobs Associates worked with Wilson Okamoto Corporation (WOC) of Honolulu on the Kaneohe-Kailua Wastewater Facility Plan for the City and County of Honolulu Department of Environmental Services and Department of Design and Construction. One of the plan’s key elements is a deep, large-diameter, 16,000-foot-long conveyance/storage tunnel constructed between the Kaneohe Wastewater Preliminary Treatment Facility (WWPTF) and the Kailua Regional Wastewater Treatment Plant (RWWTP). Kaneohe and Kailua are located on the east side of Oahu, about 10 miles northeast of Honolulu.
The tunnel will convey wastewater flows by gravity from the Kaneohe WWPTF to the Kailua RWWTP, allowing the Kaneohe WWPTF, the existing Kaneohe pump station, and the associated 42-inch force main to be decommissioned. This will let the City concentrate its operations and maintenance staff at Kailua and simplify overall operations for the City. The tunnel will also provide storage for peak wet-weather flows, preventing spills that may occur when wastewater flows exceed the capacity of the Kailua RWWTP.
McMillen Jacobs Associates is responsible for technical evaluations and design of the Kailua-Kaneohe Tunnel. The tunnel will have a finished diameter of 10 feet and will be constructed at a depth ranging from about 40 to over 500 feet, depending on the topography. Geologic conditions along the tunnel alignments vary from basalt flows beneath prominent ridges to unconsolidated clay, coralline sand, coral, and soft bay deposits in low-lying areas. Currently the project is in construction and McMillen Jacobs Associates is providing construction support services, including slurry wall construction and jet grouting inspection.