The Unique Kaneohe-Kailua Gravity Sewer Tunnel and Treatment Facilities Project

The KK Tunnel System has transformed the wastewater system and enhanced the state’s utility infrastructure, making it an easy choice for Wastewater Project of the Year



The Kailua Regional Wastewater Treatment Plant (KRWWTP), built in 1965, has undergone significant changes in 2018. A $375 million project has transformed the wastewater system and, in turn, the community.

The U.S. Environmental Protection Agency Consent Decree of 2010 required this project’s completion by June 2018. The Kaneohe-Kailua Gravity Sewer Tunnel and Treatment Facilities Project was Hawaii’s first deep tunnel and pump station, requiring a fast completion to meet the deadline. Both City and County Department of Environmental Services (ENV) pushed the project through its various phases and, with funding from the ENV Capital Improvement Project, the team met every deadline consistently for the eight years of the project’s process.

“As a result of our robust operations, maintenance, and rehabilitation program, our annual spills have reduced dramatically from about 200 in 2006 to 54 in 2017,” states Markus Owens, Public Information Officer of ENV.

The KRWWTP is unique in its three-mile long, 10-foot wide, underground gravity sewer tunnel, in addition to other unique features. Since the facility is adjacent to a residential neighborhood and an elementary school, measures were taken to protect the area from problems related to odor, noise and light, efforts that the surrounding community took note of. Said Owens, “The community was especially complimentary in our approach to inclusion, discussion, education, and mitigation of impacts, and said that this should be a model for all governmental (not just City) projects.”

Some of the project’s features include: dual drywells and wetwells, ventilation and odor systems, and sound-attenuated structures.

The project’s creation was a very involved process. Initially, there were public concerns regarding the 13-foot diameter hole being near to residential homes. The team did extensive public outreach and added a monitoring program for negative effects of the tunnel but none occurred. The tunnel’s design involved 400-foot deep borings in hard basalt. Being that it was the deepest of its kind in Hawaii, many operational safety, monitoring and alarm systems were designed. Groundwater intrusion also posed a challenge during construction; a probing and grouting program was used to combat this problem. Other project features included dual drywells and wetwells, ventilation and odor systems, and sound-attenuated structures.

The tunnel’s design involved 400-foot deep borings in hard basalt, the deepest of its kind in Hawaii.

The project’s concept was developed by ENV as an alternative method of transporting flows from the Kaneohe-Kahaluu sewer to the KRWWTP. The Wilson Okamoto Corporation and McMillan Jacobs designed the idea, and the ENV worked with various environmental groups. Lori Kahikina, P.E., was “central to the entire process,” according to Owens. This was due to her roles as ENV Director and head of the Collection System Maintenance Division. Many other individuals and companies also worked to ensure the success of this project from its conception stages to its completion.

The KRWWTP features a three-mile long, 10-foot wide, underground gravity sewer tunnel.

Honolulu Mayor, Kirk Caldwell, described the project as “one the entire community can be proud of.” The project also includes reduced energy consumption and improved environmental protection. As Hawaii’s largest ever wastewater system upgrade, it was crucial to protect the area’s unique environment while improving the infrastructure. Ray Matasci, Pacific Area Leader of Brown and Caldwell, described the goal of the engineered solution as protecting the community’s welfare without negatively impacting the environment. The Hawaii Department of Environmental Services is looking forward to maintaining the same goals in the upcoming Sand Island and Honouliuli WWTP Secondary Treatment projects as well.


Julia Edinger is the Editorial Assistant for American Infrastructure Magazine. She can be reached at


Photos Courtesy of Bowers + Kubota

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