Central Interceptor

Approximate route

The Central Interceptor is a wastewater infrastructure project in Auckland, New Zealand. The project is being undertaken by Watercare Services and involves boring a 4.5 metres (15 ft) diameter wastewater pipe underneath the Auckland central isthmus, to carry wastewater flows from parts of the city to the Māngere Wastewater Treatment Plant.

The interceptor is New Zealand's largest-ever wastewater project, costing approximately $1.5B.^[1] The tunnel was initially to run from Western Springs to Māngere,^[1] with the length of the tunnel being 13 kilometres (8.1 mi), with an additional 4.3 kilometres (2.7 mi) of link sewers.^[2] In 2021, resource consent was granted to extend the project to Tawariki St, Grey Lynn - enabling the new tunnel to connect to the Orakei Sewer Main. In May 2024, resource consent was granted to further extend the tunnel to Point Erin Reserve - giving the tunnel a final length of 16.2 kilometres (10.1 mi).^[3] When complete, the interceptor will be New Zealand's third longest tunnel.^{[citation needed]}

The project allows for population growth in Auckland and the resulting increased wastewater demands, and also aims to reduce the volume of overflow from the older combined wastewater/stormwater systems in western Auckland, which dump excess stormwater (contaminated by faeces) into the Waitematā Harbour on days of heavy rain. A notable example on 27 January 2023 resulted in a water quality alert being issued for 11 Auckland beaches because of contaminated stormwater overflows caused by heavy rain.^[4] The additional capacity of the central interceptor is expected to reduce these overflows by at least 80%, reducing the number of times per year that contaminated stormwater is dumped into the harbour from 52 days to ten or fewer.^[2]