By Shannyn Soliven
HNN Summer Intern
HONOLULU (HawaiiNewsNow) -- A three-year, $375 million project to build a gravity sewer tunnel and make other infrastructure upgrades in Windward Oahu was officially wrapped up Thursday.
The 3-mile-long tunnel is 400 feet below the surface in places, and was constructed to be able to handle "massive excess capacity," including during major storms, Mayor Kirk Caldwell said.
"This first-of-its-kind project in the state of Hawaii allows sewage to flow by the use of gravity instead of using energy and being pumped under pressure," Caldwell said, in a news release.
He added that a newly-built pump station has "state-of-the-art redundancy to avoid problems should there be a failure of one of the pumps. This is a project the entire community can be proud of."
The improvements, officially known as the Kaneohe-Kailua Wastewater Conveyance and Treatment Facilities project, are aimed at preventing overflows and spills. In addition to the tunnel and pump station, the project included a generator building and odor control facilities.
The city said the upgrades are considered the most ambitious of its 424 projects included in a consent decree with the U.S. Environmental Protection Agency and state Department of Health, ensuring improvements to wastewater collection and treatment systems on Oahu.