Key facts

There are heaps of interesting facts about the Central Interceptor. We’ll update this page throughout the project.

Project build: 2019-2025, 13km long: the longest wastewater tunnel in NZ, 4.5 metres high and 4.5 metres wide with a capacity of 200,000 cubic metres.

Facts about our tunnel

  • It’s underground - between 15 and 110 metres below the surface.

  • It’s 4.5-metre in diameter

  • It slopes downhill from Western Springs – this means wastewater can flow to Watercare’s Māngere Wastewater Treatment Plant.

  • It will have 16 permanent shafts for operational use and future access – these will collect and transfer wastewater from the existing network into the tunnel providing a more direct route to the Māngere Wastewater.

Facts about construction

  • The main underground tunnel will be connected to two smaller link sewer tunnels.

  • We’re using a tunnel boring machine (TBM) to build the tunnel.

  • The TBM travels between 15 and 110 metres underground.

  • Construction will include structures at the connection points such as access shafts, drop shafts, flow control structures, overflow structures, grit traps, air vents and air treatment facilities.

  • There will be 16 construction sites - three major sites and 13 ones.

  • Most work will occur underground.

The tunnel boring machine that will dig the Central Interceptor tunnel.
The tunnel boring machine that will dig the Central Interceptor tunnel.

Facts about Auckland’s wastewater

  • Lots of the drain pipes in central Auckland are old - when it rains treated sewage overflows into our waterways.

  • Auckland is serviced by approximately 8,000 kilometres of public wastewater pipes.

  • We’ll reduce overflows in central Auckland by up to 80 per cent when the Central Interceptor and western isthmus strategy are completed.

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More information

Central Interceptor newsletter (July 2019)
Media release (March 2019)
Media release (November 2018)
Media release (September 2018)
Central Interceptor review – Outcomes from the International Review Panel
Media release (May 2018)
Media release (March 2018)
Media release