Sour gas found at damaged Christchurch sewage treatment plant
Sulphurous gases, including one known as ‘swamp gas’, have been detected during specialist air quality tests around the burnt-out Christchurch sewage treatment plant, but council chiefs insist the fact that there is no danger to people’s health.
By Jean Edwards of rnz.co.nz
An expert monitoring team flew to the town from Hamilton last week, the same day weary Bromley ratepayers told a council meeting that the foul smell was ruining their daily lives and making them sick.
Specialists tested the type and concentration of gases in the air at several locations around the plant and nearby streets last Thursday.
Helen Beaumont, leader of Christchurch City Council, said the results showed small amounts of hydrogen sulphide from digesters and oxidation ponds, commonly known as sewage or swamp gas.
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Tests near the ponds also detected methyl mercaptan, a pungent gas that forms when organic matter breaks down.
While the readings were well above the odor detection threshold, Beaumont said they remained well within WorkSafe exposure standards.
“The reassuring news we have received from our first review of the tests is that there is nothing in the air that poses a physical risk to people’s health, although we recognize how mentally difficult the situation is. for residents who live close to the plant,” she said.
Test results will be published online once they have been peer reviewed.
Beaumont said further air quality testing would be done until decaying materials in the two fire-damaged trickle filters were removed.
“We know that the stench of trickle filters increases significantly after rain, so we will be doing follow-up sampling after the next weather event. We will also continue to monitor odors until the contractor has removed all material. trickling filters,” she says.
People who live near the plant have complained of sleepless nights, nausea and headaches, and are worried about the health effects of prolonged exposure to the smell.
While council staff told last week’s meeting that public health officials raised no direct concerns about the smell, Canterbury Medical Officer Dr Cheryl Brunton said the RNZ’s exposure to strong odors could affect people’s physical health.
READ MORE: Fixes for stench plaguing Christchurch suburbs don’t impress
“Exposure to hydrogen sulfide, a gas that can be a component of odor from damaged bacteria filters and treatment ponds, can cause nausea, watery eyes and headaches at relatively low concentrations. It can also make symptoms worse in people who have asthma,” she said.
“Even if people exposed to the smell do not experience physical health effects, continued exposure to unpleasant or noxious odors can still have a detrimental effect on their mental well-being, especially when they have a limited or no ability to avoid continued exposure.”
Brunton said people with health concerns from the smell should see their GP.
Odor monitoring from the plant – which comes from filters and oxidation ponds – is carried out by both the City Council and Environment Canterbury.
The roofs of the filters were destroyed in last November’s fire, so when it rains the decaying biomass trapped inside stinks.
The council warned there was no silver bullet, with the process of removing around 26,000 cubic meters of hazardous material from the filters expected to take up to seven months.
In the meantime, the council hopes new aerators will improve the smell of the ponds.
Advisors have pledged to provide bi-monthly progress reports on efforts to control the stench, while staff look at ways to support those struggling the most.
A spokesperson for Environment Canterbury said two staff members visit the treatment plant twice a week to record their observations of the smell, in addition to reporting from the public via the Smelt It app.