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Projects / Karori Wastewater Tunnel upgrade

Karori Wastewater Tunnel upgrade

Current status

On behalf of Wellington City Council, we are upgrading the wastewater tunnel to improve the performance of the network leading to the Western Wastewater Treatment Plant and reduce the risk of overflows into the environment.

Start Date
End Date

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

Wellington Water, 04 912 4400

Work is underway to excavate the site and construct a new chambered valve system. This will help us better manage the flow to the treatment plant and be safer for our staff to operate and maintain.

The tunnel is accessed off South Karori Road and there may be some increased traffic to and from the site.

This project continues Wellington Water’s work on behalf of Wellington City Council to reduce wet weather overflows to the Karori Stream. 

The Western Wastewater Treatment Plant (WWTP) has the capacity to treat flows of up to 200 L/s. However, if the peak inlet flows exceed this level, any additional incoming flows are diverted to the 1000m3 tank at the WWTP. If the storage tank is full, partially treated wastewater is discharged to the main outfall. If the main outfall does not have enough capacity, fully treated effluent is discharged to the stream and the remaining volume is discharged to the main outfall.

This project will reduce the risk of discharges to Karori stream by enabling better management of peak inlet flows to the WWTP.