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As ALICE, the huge tunnel boring machine, chews its way under the Auckland suburbs of Avondale and Mt Albert, it produces a continuous stream of waste– a slurry of water, clay and other materials – that must be carried away and processed. Intergroup provided and runs the wastewater treatment plant, delivering 24/7 operations. Without this treatment plant, ALICE would quickly grind to a halt.

Waste water treatment crucial to tunnelling operations

Australasia’s largest road tunnel, currently being dug under Avondale and Mt Albert by an enormous tunnelling machine, will eventually form part of the NZ Transport Agency’s Waterview Connection project. This project is one of the most important infrastructure developments, and at $1.4B one of the most expensive, ever to take place in New Zealand.

The tunnelling machine, dubbed ALICE, operates virtually round the clock.

All of the material that ALICE gouges away from the tunnel face, along with the water used in the tunnelling operation, is carried back to a wastewater treatment plant operated by Intergroup, under contract to the Well-Connected Alliance (WCA).

The treatment plant is built to handle up to 22.5l/s of wastewater. While this is considerably more than ALICE’s output, the extra capacity allows the treatment plant to catch up – emptying the buffer tanks – if needed.

Imported from Australia, the water-treatment plant will be used to support ALICE until the end of the tunnelling in late 2015.

High-quality performance to meet strict environmental discharge standards

All of the wastewater must be treated to strict standards. Although the chemical composition of the wastewater can vary widely, with fluctuating pH, the treatment plant must be able to cope and deliver clean water and solid (cake) for disposal.

The plant is largely automated – meaning that it doesn’t require an operator on duty at all times. However, Intergroup technicians regularly visit the plant to ensure that it is operating correctly and such things as chemical supplies are sufficient and feeds are functioning properly.

Intergroup’s critical role

Processing the wastewater produced by ALICE is a crucial element in the Waterview Connection project.
If the processing plant ceases operation the buffer tanks will quickly fill up. Once they are at capacity, the whole operation must shut down.

ALICE is big
  • With a cutting diameter of 14.4m, ALICE is the 10th largest machine of its kind ever built
  • ALICE weighs 3200T, is 87m long and requires 15 people to run it
  • ALICE’s average daily progress is about 10m per day
  • Breakthrough at the northern end of the project area is expected in September/October
  • The project is being delivered by the Well-Connected Alliance, comprising the Transport Agency, Fletcher Construction, McConnell Dowell Constructors, Parsons Brinckerhoff, Beca Infrastructure, Tonkin & Taylor, and Japanese construction company Obayashi Corporation