Northern Interceptor chamber completed under budget in Auckland
Watercare has freed up $7 million for other infrastructure projects after completing one of the largest concrete pours associated with the Northern Interceptor, a major wastewater project designed to support housing growth, strengthen network resilience and redirect flows to areas with available treatment capacity.
The milestone involved constructing a confluence chamber that will allow wastewater flows from Hobsonville to be redirected to the Rosedale Wastewater Treatment Plant when the Northern Interceptor comes online in October.
Programme director Rob Burchell says progress has been better than expected, reducing the cost of the connection from an estimated $25 million to $18 million.
“This has been driven by strong planning, design improvements, and proactive project management,” Burchell says.
“Delivering key components on time and under budget means we can reallocate $7 million to other projects in our $13.8 billion 10-year Business Plan (2025–2034).”
Head of wastewater Andrew Deutschle says the connection will help improve network performance as Auckland continues to grow.
“Redirecting flows to Rosedale makes better use of the treatment capacity in the north,” Deutschle says.
“Over the next decade, flows from around 160,000 households will gradually shift from Māngere to Rosedale, reducing pressure in the south and improving performance across the city.”
Project manager Paula Steinmetz says building the confluence chamber was one of the most technically demanding parts of the work.
“More than 50,000 litres of concrete have been poured to form the walls of a new confluence chamber,” Steinmetz says.
“The crew spent six hours completing the pour using a 47-metre boom pump and specialist equipment to compact concrete around tight pipe penetrations.”
The most complex section of the work was around the Wairau Branch Sewer, which sits just 150mm above the base slab and required careful placement and compaction of concrete around the existing pipe.
“Despite the difficulty, our construction partner SEIPP Construction completed the work with minimal rework needed,” Steinmetz says.
With the chamber walls now complete, crews will install a central column, two internal walls, precast roof beams and the Northern Interceptor pipework within the chamber.