We’re continuously monitoring air quality around the plant’s oxidation ponds and nearby communities.

Our new hydrogen sulphide monitoring dashboard(external link) shows the hourly averages of hydrogen sulphide measured for each location. 

Just select a location on the map to see the latest H₂S level for that monitor.

Our hydrogen sulphide monitors have been in place since July 2023, and the results are regularly published on this page.

The odour affecting nearby areas is mainly caused by hydrogen sulphide. This gas has a strong ‘rotten eggs’ smell, even at very low levels – much lower than the levels known to cause health effects. You can read more about the ways we measure and interpret hydrogen sulphide levels under ‘Odour and health’ below.

What we’re monitoring

We undertook an air monitoring programme to confirm where these gases are coming from across the treatment plant site, and measure their impact at different distances from the plant.

Our monitoring now focuses on hydrogen sulphide because previous monitoring detected no other odour-related chemicals at levels that could pose a health risk.

The monitors measure hydrogen sulphide at the following five locations:

  • Carters Road (Shortland Street North)
  • Mecca Place
  • Rudds Road
  • Shortland Street
  • South New Brighton School
     

See the latest hydrogen sulphide (H₂S) levels

Our new hydrogen sulphide monitoring dashboard(external link) shows the hourly averages of hydrogen sulphide measured for each location. 

Just select a location on the map to see the latest H₂S level for that monitor.

Please note: This dashboard provides monitoring information to support community awareness. While Christchurch City Council always works to make sure the information is accurate and up to date, data may occasionally be delayed, incomplete, or unavailable due to operational or technical factors.

Comparing levels by location 

The graph below shows the combined hourly averages of hydrogen sulphide recorded for each location last week.

The biological health of the ponds is fragile. Spikes of odour are being detected at community monitoring sites. Our teams are doing everything they can to address the current situation.

Health and previous monitoring information

When symptoms may occur

People vary widely in how sensitive they are to hydrogen sulphide. Some can detect it – or experience symptoms – at levels between 0.0003 and 0.016 parts per million (ppm).

The California Office of Environmental Health Assessment sets a guideline of 0.03 ppm, averaged over an hour, to avoid symptoms such as:

  • Nausea
  • Headaches
  • Eye, throat, or skin irritation
  • Sleep disturbance
  • Worsening asthma

At this level:

  • 83% of people can smell hydrogen sulphide
  • About 40% may experience symptoms

On our graphs, the purple dotted line represents this 0.03 ppm wellbeing threshold.

Interpreting monitoring spikes

If you see a spike above 0.03 ppm, it means that during that hour, the concentration was above the 0.03 ppm wellbeing guideline. These spikes usually occur when steady, low or moderate winds blow towards the monitor.

Health effects and recovery

Hydrogen sulphide at these levels is unpleasant and can cause short-term symptoms, but it does not build up in the body. Symptoms should resolve once the spike drops. Long-term health effects are very unlikely

Everyone responds differently, so please monitor your own symptoms. If you feel unwell, consider contacting your GP or healthcare provider.

January:

February:

March:

April:

May:

June:

July:

August:

September:

October:

November

December

Combined air monitoring results

Combined air monitoring results

Bromley School air monitoring results

South Brighton air monitoring results

Rudds Road air monitoring results

Shortland Street air monitoring results

Estuary Road South air monitoring results

Maces Road air monitoring results

House testing results: August 2022

House discolouration investigation and findings.

Christchurch City Council has received and published the findings of the houses tested for paint discolouration.  Read the report [PDF, 4.2 MB].

All houses tested were found to have had lead-based paint, with almost two-thirds showing a likely reaction between hydrogen sulphide and lead in the paint.

The remaining houses didn’t show a chemical reaction, but our expert contractors, ENGEO, noted the discolouration could be removed by washing it with a chlorine solution, as the discolouration is most likely related to mould. This mould isn’t connected to the odour from the wastewater treatment plant, but is probably mould normally found on houses.

We have been advised that the discolouration is likely to only be temporary, and a 1966 study into the effects of hydrogen sulphide on lead-based paint does not suggest permanent damage to the paint. 

The discolouration is expected to gradually reduce as daylight hours lengthen, the health of the oxidation ponds improves, and we progress through spring and summer.

Any discolouration under the eaves could take longer to fade as it won’t receive direct sunlight.

What you can do if your house is affected:

  • We expect the discolouration to fade as the health of the oxidation ponds improves, hydrogen sulphide levels drop and daylight hours lengthen.
  • Wash your walls with a commercial chlorine-based solution, or warm, soapy water. This could help remove any organic dust, common moulds and some discolouration. The presence of these common moulds is not linked to the wastewater treatment plant fire.
  • Adhere to the manufacturers’ proprietary ratio recommendations if you use a commercial chlorine-based solution.
  • Wash your house several times if required.
  • If you're physically unable to clean your house or require assistance, we can provide advice and arrange help. Contact us at wastewater@ccc.govt.nz.

What you should not do:

  • Use a high-pressure washer to try and clean any staining or discolouration, as this could result in flakes of lead-based paint entering the environment.
  • Exceed the manufacturer’s proprietary ratio recommendations if you use a commercial chlorine-based solution.

A mail-out containing the above information and updates from the treatment plant site, and health information will be delivered to 6,700 homes – including South New Brighton and Southshore – from Friday. Due to the distribution area, some residents might not receive this mail-out until Monday.

House testing results: June 2022

We've received our test results of the four houses that we sampled after concerns were raised about a black mould appearing on the exterior of some buildings near the wastewater treatment plant.

The results from a reputable external contractor have confirmed that the discolouration observed isn't due to mould. While sampling did detect the presence of various mould types, there were no spores or types outside of common mould that typically grows on the exterior of Canterbury houses. 

We're undertaking further investigations to determine what's causing the discolouration of external paint that some residents have reported. We will publish and share these results once we receive them.

Initial air quality testing results