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Wastewater Treatment Plant:  Honouliuli WWTP

Plant Detail

Honouliuli Service Area

Honouliuli Wastewater Treatment Plant (1978)

  • Advanced Primary level of treatment
  • Processed 25.21 million gallons per day (FY13)
  • Secondary level of treatment for reuse (13 mgd)
  • Deep ocean outfall (8,760 ft. offshore/200 ft. deep)
  • Estimated 20-year CIP funding: $270 million


The Honouliuli Wastewater Treatment Plant (WWTP), located in southwestern Oahu, was built in 1978 with its deep ocean outfall 8,760 feet offshore at a depth of 200 feet completed in February 1979. 


The service area for this system,  often referred to as West Mamala, extends from Halawa to Makakilo, Barbers Point and Mililani.


The Honouliuli WWTP, which was strictly a primary treatment at first, has a design capacity of 51 million gallons per  day (mgd), provides both primary and secondary treatment.  In January 1996, the completion of a secondary treatment facility allows treatment of up to 13 mgd of wastewater.  Secondary treated wastewater receives tertiary treatment via the Board of Water Supply's Ewa Reclamation Facility, for beneficial reuse in the Kapolei and Ewa areas.  The plant currently processes approximately 25.21 mgd daily.


Wastewater enters the Honouliuli WWTP through five separate interceptor sewers:  Makakilo from the west; Waipio Peninsula from the east; Ewa Gentry from the north; Ewa Beach from the south; and Barbers Point (U.S. Navy) from the southwest.


The Honouliuli WWTP operates under National Pollutant Discharge Elimination System (NPDES) Permit (No. HI0020877), effective Dec. 16, 1993.  Although the NPDES permit expired June 5, 1996, the plant operates under an administrative extension pending the issuance of a new NPDES permit by the State Department of Health.  The plant discharges a mixture of primary and R-1 treated wastewater from the facility to receiving waters in West Mamala Bay in accordance with the effluent limitations, monitoring requirements and other permit conditions.  The permit was issued under 40 CFR Section 301(h) that allows the discharge of less than secondary treated effluent if it meets specified parameters as set forth in the regulations.  Under a Consent Decree, the Honouliuli WWTP shall be upgraded to a full secondary wastewater treatment plant by June 1, 2024.

Last Reviewed: Monday, September 23, 2013