Projects / Western wastewater treatment plant outfall pipe renewal

Western wastewater treatment plant outfall pipe renewal

Current status

On behalf of Wellington City Council, we are upgrading and realigning the outfall pipe at the treatment plant after it was damaged in a slip. This work will improve the resilience of the pipe .

Start Date

If you have any questions about this work, please contact:

Wellington Water, 04 912 4400

Work to stablise the slope and build the pipe bridge started in March 2023.  The work progressed well with the slope stabilisation completed, gabion baskets installed to protect stream banks and the foundation piles complete. 

However, work is currently on hold while long-term access agreements and easements are put in place.  Negotiations are continuing constructively and we hope to be able to complete the works early in the New Year. Then there will be a period of site remediation.


The outfall pipe at the Western wastewater treatment plant carries fully treated effluent out to Cook Strait.

In February 2022, it was damaged by a slip during a severe wet weather event. The pipe was was repaired, but was damaged again by a further slip during a subsequent wet weather event.

To address this and ensure the resilience of the pipe, work is now underway to stabilise the surrounding area and realign the pipe, including building a pipe bridge to further protect it from the risk of slips and damage from severe weather events.

Until this work is completed fully treated effluent is being discharged into Karori Stream, which is being continually monitored.