The project allows for population growth in Auckland and the resulting increased wastewater demands, and also aims to reduce the amount of wastewater overflows from the older combined wastewater/stormwater systems in western Auckland, which currently, on strong rainfall days, are forced to dump excess water (contaminated by faeces) into the Waitematā Harbour.
One typical example was on 27 January 2023, when a water quality alert was issued for 11 Auckland beaches because of wastewater overflows in heavy rain.
[3] The new interceptor will be New Zealand's largest wastewater project, costing approximately $1.5B,[4] and is 13 km long (plus 4.3km of link sewers).
[4] In 2021 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 extend the tunnel further to Point Erin Reserve - giving the project a final length of 16.2 km.