Seaview Wastewater Treatment Plant Odour Monitors
To better monitor and understand odour, monitors have been installed within the Seaview plant boundary and in carefully selected locations around the community.
These monitors pick up Hydrogen Sulphide, or 'H2S' - commonly known as a 'rotten egg' smell.
These monitors pick up odour at very low levels, starting at 0.1 parts per billion (ppb).
We expect that odour levels inside the plant boundary will be greater than those in the community.
People experience odour in very different ways. Thresholds for noticing hydrogen sulphide can vary significantly from person to person. Some people may pick up light odour at 1 ppb, and others may only experience odour at 1500 ppb. The Ministry for the Environment’s air quality guideline for hydrogen sulphide is 5 ppb. This is based on preventing odour impacts on wellbeing rather than specific health effects.
To provide practical guidance, we have adopted 30 ppb as the threshold for concern for impacts on community well-being. This is also used by Christchurch City Council, and is based on guidelines from the California Air Resources Board for a one-hour average.
Worksafe regards 3,000 – 5,000 ppb (3 - 5 parts per million or ppm) as a strong odour. The New Zealand workplace limit is an average of 5,000 ppb over an 8-hour working day.
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Which way is the wind blowing?
The wind can have a real impact on when and where people experience odour. A northerly can spread odour to the areas south of the plant, and a southerly can spread it northwards. On a still day, odour can stay around the plant.
Your nose may vary
The way people experience odour varies significantly. Some people have very sensitive noses, which pick up smells that other people might not notice. The odour levels displayed are a broad indicator of when someone might smell H2S, and not definitive.
What’s that smell?
We know that hydrogen sulphide is not the only odour compound that people experience in the area. Odour is complex, and people might smell other odour compounds from the plant and surrounding environment. These graphs are not a comprehensive representation of all odour.