Means and Methods

  1. What are the specifications of the gravity sewer tunnel?
    • An approximate 3-mile tunnel from Kaneohe Wastewater Pre-Treatment Facility (WWPTF) to Kailua Regional Wastewater Treatment Plant (WWTP) will be constructed by a Tunnel Boring Machine (TBM). The TBM will drill a tunnel up to 13 feet in diameter. A pipe will then be installed and secured in place with grout (to fill the void space between the outside of the pipe and the tunnel wall). The final inside pipe diameter will be 10 feet. Since the tunnel will convey wastewater by gravity flow, it slopes down toward the Kailua Regional WWTP, starting at a depth of approximately 35 feet below ground level at the Kaneohe WWPTF, and ending approximately 62 feet below ground level at the Kailua Regional WWTP.
  2. What is the time frame for construction?
    • The current schedule for completion shows 5-years, 8-months involving three separate phases:
      1. Demolition of unused facilities to clear way for tunneling production and to accommodate influent pump station (IPS) at Kailua Regional WWTP: January 2013 – September 2013
      2. Tunnel Construction, including related improvements at Kaneohe WWPTF and Kailua Regional WWTP): October 2013 – November 2016
      3. Construction of IPS and headworks at Kailua Regional WWTP: April 2015- June 2018
  3. What will happen to the Kaneohe pre-treatment facility (PTF)?
    • The Kaneohe WWPTF will be de-commissioned. A new wastewater tunnel connection facility with odor control will be constructed within the same property boundary.
  4. What will happen to the existing force main?
    • The existing wastewater line will be used as a back-up for two years following completion of the tunnel. It will be available during emergencies; however, the City would need to bring in portable pumps to activate the force main.
  5. What is the life expectancy of the gravity sewer tunnel?
    • 100-150 years.
  6. How will wastewater get to the surface for treatment at the Kailua Regional WWTP?
    • A new tunnel influent pump station (TIPS) will be constructed to lift wastewater from the ground wet-well and pump it to the new headworks at the surface. The headworks is the start of the treatment process. Odor control systems will be incorporated.
  7. Why is the gravity sewer tunnel the best alternative?
    • A one-year effort by the City to consider two alternatives involved a three-step process. Review of the Environmental Impact Statement (EIS), a Preliminary Engineering Report (PER), and a core-working group for community outreach.
    • The tunnel is the best alternative because no above ground storage is required, view planes remain unobstructed, additional land is not required and the Kaneohe WWPTF can be decommissioned.
    • The tunnel will use gravity rather than pumping to transport the wastewater, eliminating the risk of a force main rupture along the route.
    • The 10-foot final diameter, 3 mile-long gravity sewer tunnel will store and convey flow and help prevent overflow spills, especially during storms.
    • The life cycle costs of the tunnel are less resulting in savings to the ratepayer. Because there is no pumping and flow is by gravity long-term energy costs are lower.
  8. What are some examples of gravity sewer tunnels?
    • Similar tunnels have been constructed in Atlanta, Boston, Columbus, St. Louis, Los Angeles, Portland, Sacramento, San Diego, Seattle, Chicago, Milwaukee, Cleveland and San Francisco. Examples of tunnel projects completed include: East and West Side Combined Sewer Overflow (CSO) Tunnels (Portland, OR); Northeast Interceptor Sewer (L.A., CA), Upper North West Interceptor Sections 3&4 (Sacramento, CA), South Cobb Tunnel (Atlanta, GA), Sunnydale Auxiliary Sewer (San Francisco, CA)


Community Impact


  1. How will vibrations during construction impact nearby homes, schools and businesses?
    • There may be slight vibrations created by the tunnel boring machine (TBM) that can sometimes be felt at the surface. When the machine is launched at the Kailua WWTP, it will be at a depth of 80 to 90 feet. The machine will be at a depth of 100 feet or more when the first home is reached. We do not anticipate significant vibration impacts. In reference to the San Francisco project, when the TBM was 100 feet or more below ground, no vibration at the surface above the machine was apparent.
  2. How close are homes to the tunnel?
    • Distances from the tunnel access shaft at Kailua Regional WWTP to the nearest residence (Aikahi Gardens) is approximately 330 feet (lateral). During construction of the tunnel, the TBM will be approximately 120 feet below ground level at its closest receptor (Aikahi Gardens).
  3. How did other communities manage vibration and blasting issues?
    • The San Francisco project conducted a study involving preconstruction surveys, vibration monitoring and schedule coordination with residents. The same process will be used for this project.


  1. Will there be blasting during the construction of the tunnel? If so, how long will the blasting occur?
    • Blasting will only initially occur at Kailua Regional WWTP to excavate the shaft to approximately 90 feet deep and 80 feet in diameter, and to start the tunnel in that location. Blasting is required to break up rocks so they can be removed in order to get down below ground. Blasting is estimated to take approximately 2 months.
  2. How does blasting work?
    • Contractors will calculate how large of a charge is needed and where to set it based on distance and soil conditions. Before contractors do the first blast, they will calibrate the blasts and closely monitor charges at higher risk areas.


  1. How much truck traffic is expected?
    • The tunnel boring operation will take place at the Kailua Regional WWTP site. Roughly 50 trucks a day are expected to take the remnants from the tunnel boring offsite, along Kaneohe Bay Drive. Trucking will only occur during workday hours during tunnel boring work. Truck activity will be at both ends of the project depending on the phase of construction.

Noise, Odor, Aesthetics

  1. Will the tunnel cause noise, odor or be visible to adjacent communities once it is operational?
    • The tunnel will be virtually unnoticeable. The Kailua WWTP will still be visible. The tunnel will incorporate odor control at both tunnel shafts.
  2. Excess Hydrogen Sulfide (H2S) creates odors. How will excess be managed?
    • A quicker transport of wastewater results in less odor generation. The functional design of the tunnel allows a quicker relay of wastewater resulting in less H2S. Any residual odors will be treated at odor control facilities at the Kaneohe and Kailua ends of the tunnel.
    • In comparison, a force main flow moves only when being pumped. Flow is necessary for pumping, therefore, the force main is always full of wastewater moving and stopping. Stagnant wastewater not exposed to air produces H2S. The tunnel has air in it and waste flows are continuous.
  3. The following improvements are also proposed to address odor issues:
    • Construction of a new headworks facility in an enclosed building with odor control.
    • A new dewatering building designed for minimal gas leakage while trucks load dewatered sludge for transport


  1. How does the city plan to manage noise, traffic, vibration, odor and dust during construction?
    • A comprehensive monitoring program was established in late 2012.  The program will be used during and after construction to track ground movement, vibrations and noise.  Construction of the tunnel will be virtually unnoticeable since it is underground.  Above ground construction will be done at pre-existing City & County wastewater treatment sites.  Sound reduction equipment and construction walls will be used.  A traffic management plan will be implemented to minimize queuing on public roadways.
  2. Will construction be running 24/7? What about night hours?
    • Tunnel boring could be operating continuously for 24-hours. Material excavated during the night will be stockpiled and disposed of during daylight hours. No trucking or major above-ground work is planned during evening hours. Work outside of the tunnel will be during the day.
  3. Will the project employ local labor?
    • The gravity sewer tunnel is very specialized and will require skilled trained labor. Supervisors and management personnel will require external experts to train local labor resulting in a blend of both. The City must comply with Act 86, which requires 80 percent to be local labor.
  4. How many local construction companies are able to qualify for a construction job like this?
    • A job this size requires both outsourcing and subcontracting many local firms. Most of the construction can be handled locally. A few specialized labor requirements for the operation of the tunnel boring machine must be outsourced.
  5. Where are trucks taking excavated materials? What is being done with the soil and rock after boring?
    • Materials are expected to be basalt rock for 90 percent of the tunnel. The basalt may have some commercial value for structural, aggregate or road base depending on quality. The soft material, if there are no takers, is to be hauled to a landfill where it can be used for daily cover. Currently, this material is being hauled to a site in Hauula. However, this is subject to change as construction progresses.

Possible Obstacles

  1. Will earthquakes impact the tunnel?
    • A technical engineering analysis will be conducted to confirm the pipe will perform satisfactorily during ground movement due to earthquake.
  2. What happens if there is a crack or break?
    • In the event of a crack or break while in operation, repair patches or repair sleeves will be used. During construction, defective pipe will be rejected and replaced with new pipe.
  3. Is it possible for the tunnel to leak?
    • The gravity sewer tunnel is located at least 35 feet below ground level and will be below the groundwater table. If there are leaks, the water pressure will force the groundwater to seep into the tunnel rather than sewage leaking out of the tunnel system.
  4. What are the impacts on the community, cultural resources and landscapes?
    • The City prepared an Environmental Impact Statement (EIS) that included an archaeological study and cultural impact assessment. No significant impacts were found. The reports in their entirety are included in the Final EIS Volume #1 and Volume #2
    • Prior to construction, an archaeological monitoring plan is required from the contractor. At critical shallow areas of construction, on-site archaeologists will examine excavations for signs of cultural materials. When complete, the tunnel will be totally underground with no impact on view planes or landscapes.
  5. Will the project enable new and unplanned growth in the Windward region?
    • No. The Environmental Protection Agency requires the City to implement improvements but not to accommodate more development. The Koolaupoko Sustainable Community Plan shows the projected population growth is -3.2 percent (decrease) through 2035. Decisions on land use and zoning are based on the sustainable community plan, not on wastewater systems.


  1. What is the cost of this project?
    • The project is estimated to cost $200 million. Cost estimates will be updated as design progresses.
  2. Will sewer rates and taxes be affected?
    • As with all sewer improvements, the tunnel is funded wholly by sewer ratepayer fees. Taxes (property or excise) do not fund sewer projects. The cost of the tunnel is factored into the rates already approved for the next several years.

Tunnel Boring Machine (TBM)

  1. How does a tunnel boring machine work?
    • TBMs excavate rock using rotating disc cutters in a rotating wheel called the cutter head. The disc cutters create compressive stress fractures in the rock. The rock gets chipped away and transferred through openings in the cutter head to a belt conveyor where it runs through the machine for removal from the tunnel.
    • To advance, the machine uses a gripper system that pushes against the side walls of the tunnel. The machine will then push forward off the grippers gaining thrust. At the end of a stroke, the rear legs of the machine are lowered, the grippers and propel cylinders are retracted and repositioned for the next boring cycle.
  2. How big is the TBM for this project?
    • It is approximately 13 feet in diameter and about 160 tons. Its longest assembled length will be approximately 300 feet long.
  3. Why is it named Pohakulani? What does it mean?
    • Similar to naming ships, the tunneling industry has a tradition of naming tunneling machines with a female name. To continue this, the Aikahi Elementary robotics team named the TBM “Pohakulani” which means “Rock Girl” in Hawaiian.


Outreach Process

  1. How can concerned community members get involved?
    • As part of the City and County of Honolulu’s ongoing community outreach for the Kaneohe-Kailua Sewer Tunnel Project, the City has appointed John Katahira as its community liaison during the design phase.
    • Mr. Katahira has more than 16 years of civil, sanitary and environmental engineering experience and is a licensed civil engineer.
    • Mr. Katahira is available to answer questions community members have about the project. He is available to meet with affected residents and neighborhood groups to clarify the details of the project and address any concerns. He can be reached via email at:  kktunnel@tlcghawaii.com
    • The KK Tunnel Project Hotline has also been created for community members to reach the Construction Management team by phone, (808) 445-9079 or email info@kktunnel.net, with any questions or concerns in regards to the project.

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