Kailua Regional Wastewater Treatment Plant

The Kailua Regional Wastewater Treatment Plant (KRWWTP) is a cornerstone of Oʻahu’s environmental infrastructure, protecting water quality and public health throughout the Windward side. Originally constructed in 1965 to serve the Kailua area, the facility underwent a major expansion in 1994 to support regional wastewater management and eliminate treated discharges into Kāneʻohe Bay. This upgrade converted the former Ahuimanu and Kāneʻohe treatment plants into preliminary facilities and redirected their flows to Kailua for advanced treatment.

Today, the KRWWTP serves a large portion of the Koʻolaupoko District, including communities in Kāneʻohe, ʻĀhuimanu, and Kailua neighborhoods like Aikahi Park, Maunawili, Enchanted Lake, and Lanikai. Wastewater is collected via 26 pump stations and delivered to the plant for full secondary treatment before being safely discharged through a deep ocean outfall.

The Mokapu deep ocean outfall extends over 5,000 feet offshore and lies 105 feet beneath the ocean’s surface, ensuring treated effluent is released far from sensitive nearshore waters like Kailua Bay. This engineered discharge system supports the City’s commitment to environmental stewardship by minimizing ecological impact.

In late 2025, an $11 million ultraviolet (UV) disinfection system will be completed, enhancing the quality of treated effluent with a non-chemical, energy-efficient process providing an additional layer of protection for the ocean environment.

Another milestone is the completion of the Kāneʻohe–Kailua Conveyance and Treatment Facilities Tunnel Project, a $375 million investment in resilience and reliability. This three-mile-long, 10-foot-diameter gravity sewer tunnel was constructed using a tunnel boring machine beneath the Oneawa Hills. It conveys wastewater from the Kāneʻohe Pretreatment Facility directly to the Kailua plant, minimizing energy use and reducing the risk of wastewater overflows during storm events. The tunnel also functions as a storage system to equalize peak flows—ensuring better treatment performance and environmental safeguards.

KRWWTP operates under a National Pollutant Discharge Elimination System (NPDES) Permit, effective March 1, 2025, through February 28, 2030. The permit and associated Zone of Mixing (ZOM) authorize the City to discharge secondary treated effluent to the Pacific Ocean east of the Mokapu Peninsula, in compliance with stringent effluent standards, monitoring protocols, and permit conditions.