Diggers working at the burnt-out Bromley wastewater treatment plant. (Photo supplied by council in June 2022). Photo: Christchurch City Council
A new report on the cause of the Christchurch wastewater treatment plant blaze is consistent with the findings of a fire investigator but will not be publicly released until an insurance claim is settled, the city council says.
The council-commissioned report by Fire Investigation Services Ltd found the 2021 fire in Bromley was caused by the ignition of flammable material on a trickling filter roof, after a subcontractor used an "unauthorised" heat source during repairs.
Chief executive Dawn Baxendale said the report reflected the findings of Fire and Emergency New Zealand specialist investigator Bruce Irvine, whose report was published last December.
She said there were no new factors that would affect the council's insurance claim, after a subcommittee considered the report last Friday.
"We know the local residents have had a terrible time coping with odours after the fire destroyed about 60 percent of the plant's capacity to treat wastewater," Baxendale said in a statement.
"The full report will not be made publicly available until all insurance and legal proceedings have been completed. The insurance subcommittee has requested that I release what information I can without jeopardising any proceedings.
"We are committed to resolving these proceedings as soon as possible, as we know the residents want answers."
The stench from the burnt-out treatment plant badly affected the health of people living nearby, who complained of nausea, headaches, worsening asthma and sleepless nights for months.
Last month, community advocates told the council the lingering stench had left them at breaking point and the wait to resolve the situation had left the people of Bromley "living in limbo".
A council meeting held with residents about the Bromley stench in June 2022. Photo: RNZ / Nate McKinnon
The council said staff were working through "complex" insurance and legal proceedings as quickly as possible.
The wastewater plant was fully insured and the council's insurer accepted its claim soon after the fire, the council said.
The council would not disclose how much the claim was worth but said it had spent $23 million since the fire, including the initial response, reconfiguring the plant, removing rotting material from the trickling filters and assessing the damage.
Irvine found the fire most likely started when contractors accidentally ignited maintenance tape or the fibreglass roof of one of the trickling tanks with a heating tool.
He noted investigators had been unable to determine exactly how the blaze broke out because Goleman Group contractors refused to be interviewed.
Following the release of the FENZ report, Goleman Group backed its employees' view that they did not cause the blaze.
Earlier this year, the council installed five disc and 11 vertical shaft aerators in the first of the plant's six oxidation ponds to churn more oxygen into the water and improve its biological health, at a cost of $4 million.
The smell worsened last month when the disc aerators broke down, but the council said they had now been repaired.
Average hydrogen sulphide levels remained below 0.01 parts per million - well below the 0.03ppm threshold of concern - although odours were still noticeable at times, the council said.