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Wastewater Treatment Plant:  Waianae WWTP

Plant Detail

Waianae Service Area

Waianae Wastewater Treatment Plant (1968)

  • Primary+ to Secondary (1996) level of treatment
  • Processed 3.42 million gallons per day (FY13)
  • Deep ocean outfall (6,184 ft. offshore/107,5 ft. deep)
  • Estimated 20-year CIP funding: $24 million

The Waianae Wastewater Treatment Plant (WWTP) is a secondary treatment facility serving the Waianae Coast, which consists of the communities of Nanakuli, Lualualei, Maili, Waianae and Makaha.  The facility has been operational since 1968.


The Waianae WWTP was originally a primary treatment facility with a treatment capacity of 1.72 million gallons per day (mgd).  The plant was upgraded to advanced primary treatment in 1988 expanding its treatment capacity to 5.2 mgd with a peak capacity of 13.8 mgd.  In 1996, the facility was upgraded to provide secondary treatment.


Wastewater is collected and transported to the WWTP through a pipeline along the coastline (following Farrington Highway).  Two wastewater pump stations located in Nanakuli facilitate the delivery of the wastewater to the WWTP.


Sludge generated by the facility is thickened, dewatered, and disposed in the Waimanalo Gulch Sanitary Landfill.  The treated wastewater is discharged to an ocean outfall located 6,184 feet offshore at an average discharge depth of 107.5 feet.


The WWWTP operates under a National Pollutant Discharge Elimination System (NPDES) Permit effective as of June 26, 2011, and expires April 30, 2016.  The NPDES permit and applicable Zone of Mixing (ZOM) authorizes the City and County of Honolulu to discharge secondary treated wastewater from the facility to receiving waters (Pacific Ocean) through its deep ocean outfall in accordance with the effluent limitations, monitoring requirements and other NPDES permit conditions.

Last Reviewed: Wednesday, July 24, 2013