Source: Radio New Zealand
The city council says staff are trying to minimise the odour by using all available tools to improve the ponds’ water quality.
The Canterbury Regional Council has received more than 2000 reports about a putrid stench from Christchurch’s wastewater treatment plant since the start of the year.
Offensive odours have plagued the city’s eastern suburbs following a fire at the Bromley plant in 2021, with the Christchurch City Council describing conditions at the oxidation ponds as the worst since then.
The stench left people battling nausea, worsening asthma, sleepless nights and deteriorating mental health.
A city council-organised community meeting was being held in Bromley on Tuesday night to give people an update on efforts to fix the problem and what to expect over the coming weeks.
Canterbury Regional Council acting director of operations Judith Earl-Goulet said it was considering what, if any, enforcement action against the city council might be appropriate and in the public interest.
The regional council had received 2,344 reports about unpleasant smells from Christchurch’s eastern suburbs since the start of this year, including 1,814 reports last week alone.
“Reports as far out as Wigram indicate to us that the smell is widespread and being felt across much of Ōtautahi Christchurch,” she said.
“Our team has been talking face-to-face with people in the area and we know the impact of the offensive smell is significant, with the extended length of ongoing smell particularly challenging.
“We’ve let Christchurch City Council know that they are non-compliant with their discharge to air consent condition on the basis that the smell from the plant has been identified beyond the plant boundary. Our investigation into the wider issue is ongoing.”
A November 2021 fire badly damaged the plant’s two trickling filters. RNZ / Nate McKinnon
The November 2021 fire badly damaged the plant’s two trickling filters, affecting the quality of effluent flowing into the system.
The city council said the plant’s oxidation ponds were usually healthy at this time of year but several compounding factors had contributed to the stench, including “increased loading” to the ponds and recent heavy rain.
“We expected the high levels of rain in January to help flush wastewater through the system and improve pond health – however, this didn’t happen, as it appears to have set back the algae growth in the ponds,” the council said.
“We’ve always known we’re operating the temporary plant with a narrow margin for error, as it has no extra capacity. This makes the system more vulnerable to sudden changes. While the ponds are now showing signs of improvement, much of the recovery depends on natural processes such as algae growth and oxygenation.”
The city council said staff were trying to minimise the odour by using all available tools to improve the ponds’ water quality.
Jet boats were being used to drive on the ponds to increase the dissolved oxygen.
The council was also dosing the ponds with hydrogen peroxide and balancing flow between ponds to better distribute load and support recovery.
“The dissolved oxygen levels have stabilised and are beginning to improve. The pond colour is also changing, which is another sign that conditions are starting to turn,” the council said.
“We remain focused on stabilising and improving the ponds before conducting a full review to identify any additional triggers behind this event.”
National Public Health Service medical officer of health Dr Annabel Begg said exposure to hydrogen sulphide odour from the plant could cause nausea, headaches, eye and throat irritation, skin irritation, sleep disturbance, and worsening asthma symptoms at relatively low concentrations.
“If people exposed to the odour don’t experience physical health effects, continued exposure to unpleasant or nasty, noxious odours can still have an adverse effect on people’s mental wellbeing,” she said.
“While exposure to hydrogen sulphide is unpleasant and may result in health effects, it doesn’t accumulate in the body. Any health effects would be expected to resolve when the odours are brought back to normal levels, and long-term health effects are highly unlikely.
“People experiencing health issues as a result of the odour coming from the treatment plant should seek health advice from their GP, doctor, Hauora or healthcare provider, or call Healthline free on 0800 611 116, anytime 24/7 for advice as soon as possible. In an emergency call 111.”
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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand