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Council investigating 'dreadful' stains on homes near stinky wastewater plant

Friday, 27 May 2022

Amy Harwood says her South Brighton home now looks “dreadful” because of markings she has never seen before.
Amy Harwood says her South Brighton home now looks “dreadful” because of markings she has never seen before.

Amy Harwood’s South Brighton home has mysterious dark stains on its weatherboards – and she claims it is linked to the horrible stench that hangs in the air.

The Christchurch City Council is investigating whether “reports of discoloration or stains” it has received are linked to its fire-damaged wastewater treatment plant in Bromley.

Parts of the plant, as well as the city’s oxidation ponds, are causing a pungent odour that can be smelt across east Christchurch. Many liken it to human faeces.

Jane Davis, the council’s infrastructure, planning and regulatory services general manager, said a specialist firm has been engaged to investigate the reports of stains on homes.

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Harwood says she cannot get rid of these stains, even with mould remover.
Harwood says she cannot get rid of these stains, even with mould remover.

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An example of some dark stains on a Shortland St home, which a resident says has only come up in the last month.
An example of some dark stains on a Shortland St home, which a resident says has only come up in the last month.

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“They will begin sampling next week,” she said.

'[The] smell is sometimes so bad that I have to lock myself in my room.' Kids in Bromley are being affected by a revolting smell that often wafts over the Christchurch suburb.

Harwood said she first noticed the “dreadful” stains on her home last weekend.

“I was like, ‘holy hell, where has this come from?’, because it wasn’t there a month ago.”

She said she had never seen anything like it, and she could not wash it off, even with mould remover.

“It’s horrible, it’s embarrassing,” Harwood said. “If it’s doing that to my house, what’s it doing to our bodies is kind of my biggest concern.”

Work continues at the wastewater plant, pictured here on the right, to prepare to remove the remaining smelly material.
Work continues at the wastewater plant, pictured here on the right, to prepare to remove the remaining smelly material.

Air tests conducted near the damaged plant show one of the council’s “gases of interest”, hydrogen sulphide, is, in some places, at a level that could cause headaches and nausea.

But the levels remain well below those that would cause serious health effects.

Hydrogen sulphide, also known as sewer gas, was linked to the discoloration and darkening of lead-based paint in a 1966 study.

Christchurch mayor Lianne Dalziel, left, says health concerns of residents living with the stench are “a high priority”.
Christchurch mayor Lianne Dalziel, left, says health concerns of residents living with the stench are “a high priority”.

Christchurch mayor Lianne Dalziel said she recently visited homes in Shortland St, which are next to the stinky wastewater plant, and she could see the “obvious” dark stains.

The health concerns of residents living with the stench was “a high priority”, Dalziel said. “That’s the question that we need to 100% know the answer to.”

Shortland St resident Janet Profit​ said insurers had taken a sample of the dark material on her home this week.

She wanted to know what the results were. “Not knowing what it is is the problem,” Profit said.

Helen Beaumont, the city council’s three waters boss, said the council was concerned for the wellbeing of residents living near the damaged plant.

Air testing had identified “gases of interest”, she said, namely hydrogen sulphide and other reduced sulphur compounds, such as methyl mercaptan – which has a distinctive putrid smell akin to rotten cabbage.

Dr Cheryl Brunton, Canterbury District Health Board’s medical officer of health, said continued exposure to unpleasant odours could also affect mental wellbeing, especially if people cannot avoid it.

“It is possible that some of the symptoms being experienced by people from the Bromley area are related to exposure,” she said, though she pointed out there could be other reasons for sickness, like the flu.

Brunton said anyone with health concerns should contact their GP.

Hydrogen sulphide, which has a rotten eggs odour, can be smelt at concentrations as low as eight parts per billion (ppb), according to California's Office of Environmental Health Hazard Assessment. Some studies put the number higher.

The California assessment puts hydrogen sulphide’s threshold for “annoyance” – which includes headaches and nausea – at 40ppb, though people’s sensitivity varies greatly.

These are some hydrogen sulphide levels detected by the city council so far:

These tests were not done over time, and only show a snapshot of what was in the air for a few seconds.

New Zealand’s environment ministry has an ambient air guideline for hydrogen sulphide of 10ppb to prevent “the resulting impacts on wellbeing rather than specific health effects”.

Higher levels of hydrogen sulphide have been detected inside the boundaries of the wastewater plant, including 368ppb off the oxidation ponds on May 18, but the gas rapidly dilutes in the air.

Beaumont said a meter allowing continuous sampling of hydrogen sulphide arrived on Friday and would be set up in Bromley immediately.

There were plans to get more of these meters, she said.