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Resources / Topic / Wastewater / Wastewater treatment plants / Western Wastewater Treatment Plant

Western Wastewater Treatment Plant

At the Western Treatment Plant, sewage travels through a series of screens, tanks, bioreactors, clarifiers and ultraviolet treatments before being discharged as liquid into Cook Strait in the vicinity of the Karori Stream Mouth.

The Western Treatment Plant was granted new consents on 28 July 2010. These consents will continue for 25 years (expire 28 July 2035).

In general, the consents allow WCC to:

  • discharge of treated and partially treated effluent through an existing outfall,
  • to discharge mixed disinfected, treated and milli-screened wastewater during and/or immediately after heavy rainfall,
  • the discharge of contaminants to the air,
  • and permission to occupy the coastal marine area with an outfall structure.

Resource consents

Resource consent reports

Plant performance

Current Status: Non-Compliant
Period: October 2023


The plant remains non-compliant for Biochemical Oxygen Demand (BOD) since 15 September (Geomean limit). The plants current trends project compliance by mid-November.

Please Explain letter: 

GWRC requested an explanation for the plants’ non-compliance with effluent quality. A response was provided to GWRC within the required timeframe.


No discharges in October.

Items of significance:

Outfall Repair:

The completion date for the main outfall pipeline has been delayed with work currently on hold due to a dispute with a nearby landowner. Discussions continue with the landowner and a resolution is expected soon.

 Karori Tunnel Project:

 The nearby Tunnel project has now been completed. This will improve upstream control of flow into the plant and increase resilience in the local network. It will also reduce the likelihood of discharges into the Karori stream during wet weather events.