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Published 29/05/2023

Main Outfall Pipeline undergoing maintenance

Wellington Water is undertaking planned maintenance of the Main Outfall Pipeline (MOP) near Seaview.

These consented works involve a permanent fix to a leaking internal pipe joint after an initial temporary repair last December.

The MOP is a key network asset that services wastewater management for the entire Hutt Valley.

This land-based pipeline starts at the Seaview Wastewater Treatment Plant and runs past the Eastern Bay communities of Eastbourne finishing at a short outfall 500 metres south of Pencarrow Head.

First commissioned in 1963, the MOP is responsible for discharging an eyewatering 60 million litres of treated wastewater each day, which equates to around 700 litres a second.

Wellington Water Chief Advisor Wastewater Steve Hutchison says remedial work is carefully planned and done by contractors who specialise in applying an innovative pipe joint sealing technique.

 “A section of the MOP must be first emptied to enable maintenance work. This will take three days and involve opening several scour valves along the pipeline to drain any remaining treated wastewater.

 “Our contractors will climb into the MOP [it is 1.2 metres wide] and install a German made AMEX-10 seal to a leaking internal pipe joint. This maintenance work is expected to take at least seven days,” says Steve.

 There is, overall, about 4000 (prestressed) concrete rubber ring jointed pipes within the 18.3-kilometre-long outfall pipe. While this requires ongoing maintenance, the internal sealing system is a cost-effective solution, can be installed quickly, and without long-term service disruption to the community.

 Steve says, “The seals retain joint flexibility and there is no need to excavate and replace an entire pipe section. We can also pressure test the valves, and this helps with identifying any other vulnerable joint seals.”

To meet resource consent requirements, MOP annual maintenance works must be completed during an 8-week window between May and July. 

 During the MOP maintenance, treated effluent will be diverted from the Seaview Wastewater Treatment Plant into the lower reaches of the Waiwhetu Stream from where it flows into Wellington Harbour.

 All recreational water users should follow the advice of Land, Air, Water Aotearoa (LAWA). There will be warning signage in place at the Seaview Road Bridge, Port Road Bridge, Seaview Marina Beach, and Marine Parade.

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