Kahuku Wastewater Treatment Plant
The Kahuku Wastewater Treatment Plant (WWTP) has been serving the northeastern Oʻahu community of Kahuku since 1980. Located in the Koʻolauloa District, the plant provides secondary wastewater treatment using the activated sludge process and disposes of treated water through underground injection wells.
In the early 1990s, the plant was expanded—doubling its capacity from 200,000 to 400,000 gallons per day (gpd). While it’s built to handle 400,000 gpd, the facility currently processes under 200,000 gpd on average. It serves homes, schools, a hospital, churches, and a small commercial district, while the rest of the surrounding area uses cesspools and septic systems.
After treatment, the water undergoes a final sand filtration and chlorination using liquid bleach (sodium hypochlorite) to disinfect the effluent. The clean, treated water is then discharged into six injection wells located about 100 feet underground.
Wastewater solids (sludge) are either:
Transported to the Kaneohe Pre-treatment Facility for final processing, or
Dried onsite in sludge drying beds and sent to the Waimānalo Gulch Sanitary Landfill.
The Kahuku WWTP is recognized for its excellent performance and consistently produces clean effluent. In 1998, the U.S. Environmental Protection Agency (EPA) awarded the facility first place nationally for Outstanding Operation and Maintenance.
The plant operates under Underground Injection Control (UIC) Permit No. UO-1257, effective from July 29, 2021, to July 28, 2026. This permit allows the City and County of Honolulu to continue safely using its injection well system in compliance with all environmental standards and monitoring requirements.
- Plant Detail
- Kahuku Service Area
- Secondary lefvel of treatment with sand filtration
- Processed 172,569 gallons per day (CY 2024)
- Injection well disposal (100 foot depth)