Major milestone reached at Rosedale Wastewater Treatment Plant

Watercare has reached a major milestone in its $18 million Northern Interceptor connection project, part of the Rosedale Upgrade Programme.

The work will increase wastewater capacity for Auckland's growing north-west, improve network resilience and support future growth.

Once complete, the project will allow wastewater from the north-west to be redirected from Māngere to the Rosedale Wastewater Treatment Plant, making better use of existing infrastructure and helping reduce the frequency and volume of wastewater overflows.

The latest milestone involved removing a seven-metre section of the existing Wairau Valley Branch Sewer from a newly built confluence chamber, where multiple wastewater pipelines come together before entering the treatment plant.

This work has brought the chamber into service and marks a significant step toward completing the Northern Interceptor connection, which remains on track for completion by the end of October.

This project is a key part of Watercare’s 10-year capital delivery programme, which will invest $15.2 billion in critical infrastructure, the largest investment programme in Watercare’s history.

Kaipātiki Local Board chair Danielle Grant says the Northern Interceptor connection work will give Auckland’s fast-growing north-western communities more wastewater capacity and a more resilient network.

"Currently, wastewater from Auckland's north-west is pumped to the Māngere Wastewater Treatment Plant via the Hobsonville Wastewater Pump Station.

"Redirecting these flows to the Rosedale Wastewater Treatment Plant will increase network resilience, make better use of existing infrastructure, enable growth and help reduce the frequency and volume of wastewater overflows."

Watercare project manager Paula Steinmetz says the work, delivered in partnership with SEIPP Construction, was one of the most technically challenging milestones of the project.

"Before we could progress the Northern Interceptor connection works, we had to remove a seven-metre section of the existing Wairau Valley Branch Sewer from inside a newly constructed confluence chamber.

"This enables the Northern Interceptor and the existing Wairau Valley Branch Sewer to operate as one integrated system feeding into the Rosedale Wastewater Treatment Plant."

Steinmetz says the confined working space inside the chamber meant the pipe had to be removed in two sections.

"To remove this section, we first cut it into two pieces using wire saws. Three cuts were made in total.

"Using wire saws meant all of the work could be carried out from outside the chamber, eliminating the need for anyone to enter the confined space.

"Once the pipe was cut, the two sections were lifted out using an 85-tonne crane. This approach allowed us to safely complete the work while wastewater continued flowing through the network."

Crews prepare the seven-metre section of the Wairau Valley wastewater pipeline for cutting into two sections before it is lifted.

Steinmetz says one of the biggest challenges was carrying out the work while keeping the wastewater network operational.

"The Wairau Valley Branch Sewer was cut within the confluence chamber, allowing wastewater flows to be safely diverted into one of the plant's inlet channels so that the adjacent channel can be isolated for further work.

"This enabled us to safely remove the pipe section while maintaining wastewater services and protecting the environment."

With the pipe removal complete and the Wairau Valley Branch Sewer now connected into the new infrastructure, the next steps involve completing the mechanical and electrical fit-out of the confluence chamber and carrying out commissioning activities before the new Northern Interceptor connection becomes operational.

"I'm incredibly proud of the team we've built and the collaborative approach we've taken alongside our construction partner, SEIPP Construction.

"It's this strong partnership that's helping us maintain momentum and deliver critical infrastructure safely and efficiently."