$60–$80 million sludge plant overspend fuels council scrutiny

Tuesday, 12 August 2025

The new Moa Point plant had an estimated $200m budget in 2021. This rose to $400m in 2022. Now it’s thought an extra $60m to $80m will have to be spent.

The Wellington City Council has pledged to conduct a post-mortem following a $60 million to $80 million blowout in the cost of the city’s new sludge plant. However, some councillors argue the fiasco could have been avoided if the council had not rejected earlier calls for internal scrutiny.

Councillor and mayoral candidate Diane Calvert said she had a commitment from council chief executive Matt Prosser to conduct a governance review after elected officials were, in a private meeting, told that the new waste water treatment plant budget had increased.

It is understood the extra $60m to $80m is going to be added to the bill, possibly paid via council borrowing but ultimately picked up by residents.

The new plant, at Moa Point near the southern end of Wellington Airport, had a estimated $200m budget in 2021. This rose to $400m in 2022.

The latest council cost saga comes after revelations that the cost to council to fix and reopen the Town Hall had increased by $147m, though this figure was recently scaled back by $15m to $17m.

Wellington City Council chief executive Matt Prosser has committed to a review of the sludge treatment plant blowout.

At the time of the 2023 Town Hall blowout, Calvert put up an amendment for an independent project review to figure out what went wrong. Calvert said this could have ferreted out problems that went on to hit the sludge plant budget.

Councillors Nureddin Abdurahman, Ray Chung, Sarah Free, Ben McNulty, Iona Pannett and Tony Randle voted with Calvert for the review. They lost as mayor Tory Whanau, deputy mayor Laurie Foon, and councillors John Apanowicz, Tim Brown, Rebecca Matthews, Teri O’Neill, Tamatha Paul, Nīkau Wi Neera, and Nicola Young voted against.

Abdurahman said it was likely an independent review of the Town Hall blowout could have identified and stopped the sludge plant cost escalation. Some increase in costs could have still occurred but “not to this level”.

McNulty said it was “hard to imagine” that the Town Hall review would not have helped. Pannett said a review would have done “no harm” and could have helped.

At the moment, the whole wastewater system relies on one pipeline covering the 9km between the Southern Landfill and the Moa Point Treatment Plant.

The new sludge minimisation plant would take wastewater from the treatment plant, and heat it to dehydrate it before feeding it to bacteria.

It makes something like a “baby food” for the bacteria that digest the sludge, allowing them to break it down quickly and easily.

A by-product of the anaerobic digestion process was natural gas, which would be transformed back into power to keep the plant running.

At the end of the process was a dry, innocuous product with a texture similar to cat biscuits and a “musty” smell similar to a dried fertiliser.

Councillor Diane Calvert, a mayoral candidate, had her bid for a review of the Town Hall project rejected.

Brown, who chairs the Environment and Infrastructure Committee, said said there was only ever an 80% chance of the project being delivered on budget. He would not give details of the extent of the blow-out.

“I was always very, very aware of the potential for the cost blowout,” he said. He understood the construction of the plant was loosely within budget but the blowout came in commissioning it, including linking it to the existing network and getting an operator.

The Town Hall cost increase came down to internal council errors while the sludge plant did not appear to come down to management, he said.

Foon said there appeared to be no need for a Town Hall review because it was clear what had gone wrong but she backed the sludge review, “because it is a major project and it had high risk all along”.

Wellington is spending half-a-billion dollars to solve a stinky problem most residents haven’t even thought about: sewage sludge.

Questions put to the council and mayor – including the new cost, whether there was a risk of further blowouts, what contributed the the increase and if recent staff turnover was a factor – were not answered.

Whanau deferred questions to the council, where spokesperson Richard MacLean said said the first briefing to councillors, on July 31, was confidential because “we still didn’t have the facts”. The council had committed to making them known at a public briefing on Thursday.

“There will be an independent post-project review, which will include all aspects of the project including governance,” he said.