An earlier report suggested trapped air bubbles were to blame for disrupting the flow of wastewater, sending it back into the plant, flooding it.
The new report details apparent design flaws in the facility, such as critical electrical equipment being located below ground, the abence of sensors or alarms for high water levels, and air relief valves on the plant’s outfall pipe being too small and potentially being stuck shut.
The failure happened while the plant was undergoing upgrade work on its UV channels, reducing its capacity.
“Hydraulic risks associated with directing increased flow to the bypass pipe were identified during risk assessment activities under the UV renewal project but were not resolved.
“An assessment of the hydraulic and air handling capacity of the altered wastewater treatment plant configuration does not appear to have been carried out.”
Five prior “inundation events” happened before the major disaster, it states.
“Potential mitigations, including limiting total inflow to the plant, were identified but were not implemented before the February 2026 flooding incident.”
Our newsroom previously revealed an “overflow event” happened hours before the disaster, but crews “took lunch” before eventually shutting the plant down and going home.
A timeline of the night shows the situation at Moa Point started going awry at 11.17pm, but no immediate action appeared to have been taken by operator Veolia, because of an unexplained “comms failure”.
The duty manager did not turn up at the site until 1.34am, after Fire and Emergency New Zealand had responded to smoke and heat alarms there and left.
It was not until 1.59am that the duty manager started a shut-down of the inlet pump station.
Veolia held a “risk register” for the plant, which the Aecom investigation obtained, but noted it “does not appear to include the risk of significant flooding”, despite previous flooding incidents.
A Veolia spokesman has hit back at the new findings, saying unlike the Crown review, the Aecom report “is not independent nor is it a complete view of the situation”.
The spokesman said Veolia was not in charge of the upgrade works and “did not make the decision to classify the UV installation as a business-as-usual process”.
“This is why standard remote monitoring staffing routines that had worked successfully for 28 years were being followed and staff were offsite when the incident occurred.”
As soon as staff arrived on-site, they took action, the Veolia spokesman said.
“Veolia is the only operator in New Zealand that has the expertise to deal with a crisis of this scale.”
Tiaki Wai chief executive Michael Brewster said the release of the report had “taken slightly longer” than he would have liked, because of insurance issues.
“We understand that people want as much information as they can get and we’ve been open in our commitment to make it available as soon as possible,” he said.
“The findings have directly informed our ongoing work to strengthen resilience across the region’s wastewater network, and as we’ve said we are well underway with the fix.”
The Government’s investigation, released on February 1, revealed a string of systemic failures, governance issues and historical underinvestment all contributed to what it called “one of the most significant infrastructure incidents experienced in Wellington in recent decades”.
Ethan Manera is a Wellington-based journalist covering Wellington issues, local politics and business in the capital. He can be emailed at ethan.manera@nzme.co.nz.