'70% confident': Moa Point races to reopen after catastrophic failure

After 10 months and millions spent on repairs, Wellington’s Moa Point sewage treatment plant is hoping to resume operations this week.

The plant suffered a catastrophic failure in February, with more than 14 billion litres of untreated sewage pumped into the sea off Wellington’s south coast.

Multiple reports have been released since, including a Crown Review which highlighted years of systemic and governance failures across organisations including Wellington Water and Wellington City Council.

The first stage of treatment is due to resume on Thursday.

Officials took media on a tour of the plant last week to see work underway, including the primary sedimentation process.

During the tour Tiaki Wai’s plant recovery director Steve Hutchison told the Herald he is 70% confident they will be ready to restart treatment this week.

Moa Point recovery director Steve Hutchison and Tiaki Wai Chief Operating Officer Charles Barker. Photo / Grace Symmans

The Herald has since sought an update on the likelihood of operations resuming in two days’ time.

In a statement, Tiaki Wai chief operating officer Charles Barker said: “the team is working through the final checks before we confirm that we can safely restart the first stage of treatment at the Moa Point Wastewater Treatment Plant on our target date, which remains 12 November at present”.

“The restart is also weather dependent as we must complete some final crane operations. We will advise the community of any significant change.

“When we restart the plant, we will advise the directly impacted community first, and then the media and other stakeholders.”

The first phase of recovery is getting the primary sedimentation room back online, so sewage can be screened before moving through to secondary treatment. The third stage is ultraviolet disinfection lights which won’t be started until the biological material is back up to the standard where UV can be effective.

The UV room where the flooding occurred during the catastrophe is still undergoing a complete system upgrade.

The UV room where the flooding occurred on February 4.

In the first stage of recovery, the plant will be able to treat 250 litres per second. On a usual day 810 litres per second of water goes through the plant.

The slower start is driven by the need to safely grow the micro-organisms which treat the sewage, but Tiaki Wai hopes over five weeks the plant will be able to take 900 litres per second.

Normally there are three primary sedimentation tanks operating in parallel; by November 12 one tank (also called a train) will be back operating, Hutchison said.

“We’re just going to start up the first train first, build up our biological material, our biomass in the next stage of the treatment process, and then we’ll bring the second train on and then the third train on.”

Two of the three primary sedimentation tanks. Photo / Grace Symmans

Barker said although recovering the plant is nothing to celebrate, it is a “massive effort”.

“Tiaki Wai have got a lot of expertise from overseas and all combined to provide a high performing team that’s allowed us in 10 months to go from what was, you know, what is on the record as a catastrophic event, to getting back onto the path of starting the plant and reducing the environmental impact.”

He said international visitors to the plant have been impressed with the progress in a short span of time.

On February 4, multiple rooms were flooded including the “sludge gallery” where yellow tape still marks the height floodwaters reached.

Flooding reached the height of the yellow marker at the centre, top of this photo. Photo / Grace Symmans

The facility is expected to be fully restored by February, but improvement work for the hydraulic capacity of the bypass and outfall, underway before the flood, will not be completed until late 2027 or 2028, Barker said.

Current estimates suggest the work will cost $53.5m (mostly covered by insurance) with $10.9m of council funding going towards repairing the defective bypass pipe.

During the repairs the team has used the opportunity to refurbish other parts of the plant, Barker said.

“I think that’s what the community would expect us to do is fix the plant but also take every opportunity to make the plant better.”

Temporary measures are in place to stop a repeat of the disaster, including not reducing the plant to half capacity again, 24/7 manning of the plant and new controls.

Barker said until the plant is fully repaired there is still the risk of discharges into Tarakena Bay.

“The first 3000L/s gets treated and the next 1,000L/s gets screened and passes down the long bypass.

“Flows over 4000L/s are very rare (i.e. during very extreme weather events) but they would exceed plant capacity, which would result in a short outfall discharge of the excess flows.”

While remediation work is underway Tiaki Wai expects the short outfall will need to be used again.

“That’s a really hard ask for our community to have to go back and tolerate because it is intolerable,” said Barker.

Hutchison said once the upgrade project is complete, there will be “a lot less upgrades and repairs”.

“There’s still always maintenance work that you need to do at an operating treatment plant, but a lot less.”

Grace Symmans is a Wellington-based reporter who covers news in the capital. Grace joined NZME in 2025 as a producer for Wellington Mornings on Newstalk ZB. She can be emailed at grace.symmans@nzme.co.nz.