A major pipeline in Tauranga is damaged and needs replacing more than a decade ahead of schedule at an estimated cost of more than $83 million.

But the replacement project, in its early stages, is already raising red flags for tangata whenua.

The ocean outfall pipe carries all of Tauranga's treated wastewater 960m out to sea off Papamoa Beach at Sunrise Ave.

According to a report presented to Tauranga City Council's Wastewater Management Review Committee this afternoon, the "critical asset" is in "poor structural condition".

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Wally Potts, the council's drainage services team leader, said the 1.9km pipe was damaged in a storm during the installation process circa 1976.

An aerial view of the Te Maunga Wastewater treatment plant. Photo / Google Maps
An aerial view of the Te Maunga Wastewater treatment plant. Photo / Google Maps

As a result, the pipe has never been able to withstand the peak volumes it was intended to carry without the risk of failure.

A resource consent, due to expire in 2040, allowed the pipe to discharge treated wastewater into the ocean at a peak rate of 900 litres per second - the level needed to accommodate Tauranga's predicted growth to that date.

Because of the damage, however, the peak level is kept below 600 litres per second to lessen the potential of it bursting.

A section burst in the early 2000s and was repaired.

As the Western Bay grew, demand on the pipe increased. The situation became more acute when the $107m Southern Pipeline was commissioned in February.

"The peaks are getting peakier," Potts said.

Based on growth predictions, the full length of the outfall pipe would need to be replaced by 2028 - 12 years ahead of schedule.

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The ocean outfall pipe - in yellow on the left - is the only pipe that carries 100 per cent of Tauranga's treated wastewater. Graphic / Tauranga City Council
The ocean outfall pipe - in yellow on the left - is the only pipe that carries 100 per cent of Tauranga's treated wastewater. Graphic / Tauranga City Council

A project to replace the end of the pipe on land - expected to cost around $15m - is at the consenting stage and the council hoped to finish construction within two years, Potts said.

Work was starting on options for replacing the marine end by 2028 - a project with an early cost estimate of $68m.

It was the question of how to handle excess treated wastewater in the meantime that had some tangata whenua representatives at the meeting alarmed.

Carlton Bidois of Ngati Ranginui was not happy with the suggestion Pond 1 could be used to store treated wastewater to help balance the wastewater system.

Pond 1 - used to store waste activated sludge - was in the process of being decommissioned after breaching a resource consent.

Bidois said he understood that once decommissioned, the pond would be returned to a natural state.

He recalled no mention of using it to store treated wastewater in the years of decommissioning negotiations.

"You knew the failures of the outfall pipe since its inception ... I really feel like we've been led up the garden path."

Council staff and elected members said they understood the decommissioning related to the sludge, and did not rule out future uses for the pond.

Potts said any future use of the pond - and what it would mean if it could not be used - was something that could be discussed as part of the project and the council was happy to have those discussions with tangata whenua.