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Published 23/01/2020

Trucks transport sludge as preparations for pipe repair begin

Trucking operations are continuing as an alternative to the sludge pipeline between Moa Point Treatment Plant and the landfill at Carey’s Gully.

The pipeline failed last week, and a repair could be a month away or longer. No wastewater or sludge was discharged to the environment as a result of the failure, which occurred in a wastewater tunnel beneath Mt Albert.

Investigations have located the point of failure and work is under way to plan a repair with a temporary bypass, as well as a long term fix. It will be a complex job, because wastewater also flows within the tunnel towards Moa Point, making for dangerous working conditions.

With the pipeline out of action, there is a risk that if the trucking option is interrupted for 24 hours or more, some sludge may need to be discharged via the long outfall pipe that carries treated wastewater out to Cook Strait.

When the plant was built, the intended alternative to pumping sludge to the landfill in the event of a significant failure was to discharge it via the long outfall. Public expectations have changed since then however, and Wellington Water and teams of contractors are making every effort for this not to happen.

The trucking system is keeping up with daily demand, but because treatment operations at the plant and the landfill were not designed to load and unload sludge from trucks, there remains a risk that we may have to discharge sludge from the outfall.

Wellington Water is also working across a number of other options for the pipeline repair and to manage the sludge volumes.

  • The treatment plant discharges over 70 million litres of treated water a day.
  • Just over a million litres of sludge is produced at the plant a day. This is being transported by truck to the landfill.
  • The sludge pipeline from the treatment plant to the landfill runs for 9km. It consists of two pipes, which operate one at a time, to allow for maintenance. It is highly unusual that they both have failed.

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