Frequently asked questions
Why do we need the Central Interceptor?
In 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.
Do we have consents for the work?
We obtained all required resource consents and landowner approvals for the Central Interceptor project in 2015, including consents for the above-ground sites. We will be working within our resource consent guidelines. See the consent documentation.
What is the Central Interceptor?
The Central Interceptor will be the largest wastewater tunnel in our history. It’s a 14.7-kilometre long and 4.5-metre wide tunnel that runs between Grey Lynn and the Māngere Wastewater Treatment Plant, collecting and transferring wastewater for treatment and safe disposal.
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. Visible construction will be contained to the 17 sites where shafts will be built and connections made to local sewer networks and overflow points.
When will construction start at each site?
This year construction started at our Māngere Wastewater Treatment Plant and May Road (Mt Roskill) sites. The project will be completed in 2025. We’ll regularly update our 'what's happening' information page with construction plans and details for each site.
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 between 15 metres to 110 metres (at its deepest point) underground.
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 Grey Lynn to Māngere. Gravity helps wastewater flow to the Māngere Wastewater Treatment Plant.
What will happen to the dirt and rock that is removed when boring the tunnel?
Not all dirt and rock is able to be reused. Any good quality material taken from the tunnel during construction will be used to rehabilitate a former mining quarry on Puketutu Island. One day, this island will be opened to the public as a regional park.
Please get in touch with our main works contractor:
Phone: 0800 425 802