Central Interceptor

The Central Interceptor is an upcoming Watercare Services infrastructure project to bore a giant wastewater pipe underneath the Auckland Central Isthmus, to carry wastewater flows from parts of the city to the Mangere Wastewater Treatment Plant.
Apart from being intended to allow for population growth in Auckland and the resulting increased wastewater demands, it also is aiming 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. The new capacity is expected to reduce these overflows by at least 80%, reducing the times per year that contaminated stormwater is dumped into the harbour from 52 days a year to 10 or fewer days. Sixteen access shafts, up to deep, will be constructed.
The new interceptor will be Auckland's largest wastewater project in history, costing approximately $1.2B, and being 13 km long (plus side branches), and 4.5m diameter. It is to run from Western Springs to Mangere.
Construction.
The construction contract was signed in March 2019 with the Ghella Abergeldie Joint Venture. Construction is expected to be from 2019 to 2024.
Construction will be via tunnel boring machine, and the course will take the tunnel 15m underneath the Manukau Harbour, though (due to the height of the Central Isthmus), in other areas if will be as much as 110m below properties.
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