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Wastewater Treatment Plant:  Waimanalo WWTP
Waimanalo Service Area

Waimanalo Wastewater Treatment Plant (1969)
  • Secondary level of treatment with sand filtration
  • Processed 527,300 gallons per day (FY13)
  • Injection well disposal (200-220 foot depth)
  • Estimated 20-year CIP funding:  $15 million

The Waimanalo Wastewater Treatment Plant (WWTP) is a secondary treatment facility that serves the Windward shore from Makapuu Point to Bellows Air Force Station.  However, not all of that area is sewered and a portion still uses cesspools and septic tanks to process residential wastewater.


The plant was built in 1969 and put in service in 1972. The state of Hawaii, DLNR, originally owned the facility, but it was operated and maintained by the City since 1972 in an agreement with DLNR. The State officially turned over the plant to the City in 2012. 


Recently, the state spent about $28 million to upgrade the facility and is in the process of turning over the plant to the City.


Sludge generated by the facility is taken to the Kailua Regional WWTP for final processing before being sent to the Waimanalo Gulch Sanitary Landfill.  The secondary treated effluent is further processed through a filtration system. This facility has a sodium Hypochlorite disinfection system  that disinfects the effluent before injecting it into the 10 underground injection wells. These underground injection wells are approximately 200 feet deep where the treated wastewater is discharged.


The Waimanalo WWTP operates under an Underground Injection Control (UIC) Permit (Permit No. UO-1259) effective Aug. 30, 2013, and expiring Aug. 29, 2018.  The UIC permit authorizes the City and County of Honolulu to discharge secondary treated wastewater effluent from the facility to the receiving subsurface environment through its injection well system in accordance with effluent limitations, monitoring requirements and other permit conditions.

Last Reviewed: Thursday, September 12, 2013