Watercare gets on with connecting the Northern Interceptor in Rosedale Wastewater Treatment Plant

The connection of a new 10-kilometre wastewater tunnel to Watercare’s Rosedale Wastewater Treatment Plant will help to reduce wet-weather overflows when it’s completed next year.

Work is currently underway on a $25m project to enable stage one of the Northern Interceptor to be brought into service.

Watercare is working with construction partner, SEIPP Construction, to connect the first 10 km section of the Northern Interceptor into the Rosedale Wastewater Treatment Plant.

Photo: Crews open trench to start bringing the Northern Interceptor into the Rosedale Wastewater Treatment Plant back in late May.

Watercare head of wastewater planning Andrew Deutschle says the completion of the connection works at the treatment plant will enable Watercare to redistribute wastewater flows away from the Māngere Wastewater Treatment Plant.

“Currently, flows from Auckland’s north-west are being directed to Māngere Wastewater Treatment Plant from the Hobsonville Wastewater Pump Station.

“Redirecting flows away from Māngere to the Rosedale Wastewater Treatment Plant will help to improve network resilience, make better use of current assets in our network and reduce the frequency and volume of overflows.

“Once the Northern Interceptor is plugged in, we’ll be able to get on with a billion-dollar investment programme to support planned and future growth in Auckland’s north-west, between 2026 and 2040.”

These projects are:

• Extending the Northern Interceptor to Westgate by 2029 and to Henderson by 2036.

• Connecting in the final stage of the Whenuapai and Red Hills wastewater scheme into the Northern Interceptor in 2028.

• Completing upgrades to a digester and reactor clarifier at the Rosedale Wastewater Treatment Plant by May next year.

Watercare project manager Paula Steinmetz says work to connect the Northern Interceptor to the Rosedale Wastewater Treatment Plant is going smoothly, with much of the initial groundwork already complete.

“Next on the schedule is the start of foundational work on the confluence chamber and lining the final section of the Wairau Valley Branch Sewer.

“A confluence chamber is a collection point, where different pipelines merge and connect into the wastewater treatment plant.

“This sewer, along with the future Rosedale Rising Main, will also connect into the new confluence chamber alongside the Northern Interceptor.

“The rising main section of the Northern Interceptor and discharge chamber has been installed and the gravity section to the confluence chamber is currently being constructed.”

Steinmetz says preparation is also underway to commission the new septage facility, where tankers will be able to discharge wastewater directly into the plant.

“Although much of the project is focused on the works in the plant, our crews are also installing six odour filtration domes along the interceptor’s pipeline route.

Photo: One of the six odour filtration domes being installed along the Northern Interceptor route back in June.

“These domes filter out any unpleasant smells from the air released by the air valves.

“Air valves are commonly found on large pressure pipelines, such as the Northern Interceptor, to allow for efficient operation by releasing air that accumulates during use."

Steinmetz says from this month [subs note: September 2026] crews will also begin lining work for a 200-metre section of the Wairau Valley Branch Sewer to give it added longevity as well as protection while the confluence chamber is being constructed over it.

“It’s always challenging to do civil construction works during the winter season, especially on an established and active site like the Rosedale Wastewater Treatment Plant.

“I’m proud of the excellent team we’ve built and the collaborative approach we’ve taken.

“It’s this strong partnership that’s helping us maintain momentum and deliver the infrastructure safely and efficiently.”