FAQs

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What was the RMA/consenting process?

We obtained all required resource consents and landowner approvals for the Central Interceptor project in 2015, including consents for the above-ground sites. See the consent documentation.

What is being built?

The Central Interceptor is the largest wastewater project in our history. It’s a 13-kilometre long and 4.5-metre wide tunnel, between Western Springs and the Māngere Wastewater Treatment Plant for collecting and transferring wastewater for treatment and safe disposal.

Why is the Central Interceptor being built?

In the older parts of central Auckland, wastewater and stormwater flow into a combined network of pipes. When it rains, stormwater overwhelms these pipes that are designed to overflow into our waterways. 

We want everyone to be able to enjoy clean waterways, beaches and estuaries – so we’re building the Central Interceptor. The project is an integral part of our long-term strategy to effectively manage wastewater within the Auckland region, to protect public health and the environment, and to provide for growth.

When will construction start?

We anticipate that construction will start at two sites in mid-2019: Māngere Wastewater Treatment Plant, May Road in Mt Roskill. The project will be completed in 2025. We’ll regularly update our site information page with construction dates and other site details.

How is the Central Interceptor being built?

Most of the construction work will be underground. We’re using a tunnel boring machine or TBM, to bore through the earth’s substrate and lay segments of the tunnel as it goes. The TBM will travel between 15 and 110 metres underground helping to reduce construction effects on residents and local roads.

What is a tunnel boring machine?

A tunnel boring machine (TBM) bores through the substrate and lays partial segments of the tunnel as it goes. Dirt and rock (spoil) is removed along the tunnel and out of a nearby shaft. Tunnel segments are also conveyed to the machine along the tunnel as it is created.

How deep is the tunnel?

The tunnel is 15 metres deep at the lowest point, under Manukau Harbour, and 110 metres at the deepest point, in Hillsborough.

Why is the tunnel different depths underground?

The tunnel is being built under basalt rock and the depth of this rock varies along the length of the tunnel. The tunnel slopes downhill from Western Springs helping the wastewater flow by gravity to the Māngere Wastewater Treatment Plant.

What will happen to the dirt and rock that is removed when boring the tunnel?

We’ll use the dirt and rock (spoil) taken from the tunnel during construction to rehabilitate a former mining quarry on Puketutu Island. One day, this island will be opened to the public as a regional park.