Get the latest news and meeting reports on the wastewater treatment plant recovery. We'll be updating this page as required if the situation changes or there is new information.

Latest news and updates

Clarifier 4 repairs starting 

14 March 2025

Essential repairs to one of the Christchurch Wastewater Treatment Plant’s four clarifiers are now complete. Work to repair leaks in Clarifier 3 went well and our team was able to complete this work six days ahead of schedule. The clarifier is now back in service.

Because of the success of the repair to Clarifier 3 we've decided to proceed with repairing leaks in Clarifier 4. We had planned this for later in the year but have brought the essential work forward so we can use the same team and make the most of a good weather window over the next couple of weeks. 

The repairs will start on Monday 17 March, and are expected to be complete by Friday 28 March.

The reduction of our temporary activated sludge plant to 50% capacity to enable these works is resulting in some odour. This is due to the increased load on the oxidation ponds. So far, the increase in odour isn't significant and seems to be localised to the area around the ponds/plant and along Cuthberts Road. 

We're monitoring plant operations closely during this time and will continue to do all we can to complete the repair to Clarifier 4 as quickly as possible. 

New aerator in action

We've replaced one of the aerators on oxidation pond 1. The new aerator is a lot more efficient than the old one, and we're assessing whether it will have any impact on odour while it gets up and running, as it might be disturbing sludge at the bottom of the pond. Over time it will have a positive impact on odour as it will increase aeration.

Work to repair clarifier leak starting

28 February 2025.

Essential repairs to one of the Christchurch Wastewater Treatment Plant’s four clarifiers could result in a period of increased odour.

On Monday 3 March work will begin to repair a leak in Clarifier 3. Sorting the leak will get the clarifier working at full capacity, which needs to happen ahead of more extensive work on Clarifier 4 planned for next summer.

Our temporary activated sludge plant will be reduced to 50% capacity to enable this work. This will result in increased load to the oxidation ponds, which may cause odour. The intensity and frequency of odour will be influenced by many factors including weather conditions.

We’re doing all we can to complete the repair as quickly as possible. We expect work to be complete by Tuesday 18 March.

Increase in midges

22 January 2025.

The wet weather in late December 2024 and January 2025 has had a positive impact on the biological health of the ponds. The volume of rain means wastewater entering the plant wasn’t as strong, and as a result, algae are flourishing.

Algae helps the pond system operate well by generating oxygen within the ponds and preventing the anoxic conditions which can cause odour. The fragile health of the ponds is demonstrated through Fire Investigation Report – Shuttle Drive, Bromley, Christchurch City(external link).

Consequently, we have not had an opportunity to consider it fully. Our own investigation is ongoing and we will not be commenting further.

Snapshot of hydrogen sulphide levels decrease

2 November 2022.

This graph shows how the hydrogen sulphide levels coming from the oxidation ponds have significantly decreased over the four months from 10 June to 10 October 2022.

The activated sludge plant was made operational on 28 July, with the biology reaching full maturity on 17 August, despite the challenges of growing the biology over the middle of winter. 

It took four weeks for the better-quality wastewater to flush through our network of six ponds, with the odour substantially reduced by mid-September. This was in line with the timeframes that we promised the community we'd work to.

Hold off from cleaning your house

30 September 2022.

With hydrogen sulphide levels dropping and the days warming up, it might be tempting to clean any discolouration off your house that might have been caused by a chemical reaction between lead paint and hydrogen sulphide. 

We ask that you keep waiting. Before we begin encouraging people to clean their homes, we'd like to see at least four weeks of low hydrogen sulphide levels and improved weather to get an idea of how any discolouration fades. 

We're about to start monitoring some 'test houses' and will provide updates on our website to show how the discolouration improves. 

If you absolutely must clean your house now, make sure you're familiar with our list of dos and don'ts that we published last month. 

Do:

  • Read the report findings and information(external link) on house discolouration. 
  • 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.
  • Several washes might be required.

Don't:

  • Don't 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.
  • Don't exceed the manufacturer’s proprietary ratio recommendations if you use a commercial chlorine-based solution.

Our team is keeping a register of homes that have reported paint discolouration. If your home has discolouration and you haven't let us know, or if you'd like more advice about what to do, email wastewater@ccc.govt.nz.

Newsline stories

2024 Newsline stories


2023 Newsline stories


2022 Newsline stories


2021 Newsline stories

Newsletters

2025 Newsletters

2024 Newsletters

2023 Newsletters


2022 Newsletters


2021 Newsletters

Meetings, minutes and reports

11 March 2024

Christchurch Wastewater Treatment Plant Odour Mitigation Plan [PDF, 3.4 MB].

7 July 2022

Christchurch Wastewater Treatment Plant  meeting between CDHB, ECAN and Christchurch City Council.

Action points:

  • Proceed with the setting up of the continuous monitors at the agreed sites.
  • Work with comms regarding the best way to display data on website from continuous monitors.

30 June 2022

Christchurch Wastewater Treatment Plant  meeting between CDHB, ECAN and Christchurch City Council.

Action points:

  • Circulate notes for confirmation
  • Circulate report on SIFT – MS sampling when available
  • Prepare draft/updated information for Council website.

23 June 2022

Christchurch Wastewater Treatment Plant meeting between CDHB, ECAN and Christchurch City Council.

Action points:

  • Send invitations to Medical Officer of Health for the Council meeting on 30/06

21 June 2022

Wastewater Treatment Plant Communications Advisory Group minutes [PDF, 592 KB].

9 June 2022

Christchurch Wastewater Treatment Plant meeting between CDHB, ECAN and Christchurch City Council.

Action points:

  • Report on Summary of completed sampling to be prepared.
  • Continue deploying H2S meters.
  • Ecan make available information from SO2 and H2S monitoring when available.

Timeline

Timeline of key events and decisions

November 2021

  • On 1 November 2021, emergency services respond to a fire at the Wastewater Treatment Plant in Bromley. Both of the trickling roof filters collapse. The damage couldn't be assessed properly until the fire was completely out.
  • On 4 November, the Council installed a sprinkler system to remove hot spots and help reduce the smell. We also begin working on an adaptive management plan to figure out the best possible outcome for the discharge of wastewater from the plant.
  • On 26 November, the fire is officially completely extinguished by the fire service. The Council identifies the need to remove the two trickling filters. Both filters store 13,000 cubic metres of material.
  • The Council started using misters and polyaluminium chloride - an odourless powder that dissolves in water - to help suppress the smell. Polydosing also settles more of the suspended solids in the wastewater, improving the water quality as it progresses through the plants.
  • Hydrogen peroxide - a compound that naturally breaks down into water and oxygen – starts to be added to the wastewater before it’s discharged into the oxidation ponds.

December 2021

  • On 6 December, the Council completed a successful trial to remove a section of the fire-damaged media from the plant. This means the Council could begin assessing the stability of the structures.
  • On 17 December, Council staff planned to convert two of the plant’s four clarifier tanks (or secondary contact) into aeration tanks. Installing four aerators in each of the two tanks will help decrease the bad smells and improve the quality of the wastewater being discharged. The Council anticipated that it would be years before the trickling filters could be replaced or rebuilt.

February 2022

  • On 14 February, aeration components begin to arrive to implement the interim plan to minimise odours from the fire-damaged plant.

March 2022

  • On 16 March, eight aerators are installed in two of the plant’s four clarifiers.
  • Soon afterwards, increased odours from the trickling filters are detected after wet weather. It's determined that the acute stench is caused by the material inside the trickling filters rotting and drying out.

April 2022

  • On 6 April, the aerators installed in March are turned on.
  • On 12 April, the Council decided to fast-track the appointment of a contractor to remove the burnt filter material.

May 2022

  • Filter media removal work starts.
  • On 6 May, independent testing to better understand the odours from around the fire-damaged plant detects small amounts of hydrogen sulphide and methyl mercaptan.
  • On 26 May, the Council confirms a community support package for 3,380 of the most affected residents.

June 2022

  • Southern Demolition and Salvage Limited conducted a test run, removing and transporting the burnt trickling filter material on Friday 3 and Saturday 4 June.
  • Work to remove the trickling filter began on 6 June.

July 2022

  • The new activated sludge treatment process becomes fully operational at the plant.
  • This new system pumps wastewater from the converted aeration basins to the clarifiers, which greatly improves the quality of the wastewater.

August 2022

  • Trickling filters are emptied one month ahead of schedule.

September 2022

  • Odours from the oxidation ponds are expected to reduce from September, although it is expected that some odours will remain for most of the month. These will progressively reduce as the pond's health improves.

April 2023

  • A project to increase the biological health of Pond 1 is completed after 16 aerators are installed and turned on, churning more than 300kg of oxygen into the pond every hour.
  • In the long term, these aerators will ensure the entire pond continues to stay healthy and function well.

May 2023

  • The disc aerators on Pond 1 failed and were in the process of getting repaired.

Late 2023

  • Fencing around oxidation ponds was installed to improve safety and reduce rubbish entering ponds. Subsequent minor changes were made to deter birds and improve effectiveness.
  • Insurance negotiations were continuing.
  • In November, a report on the insurance claim for the November 2021 fire was provided to the Council. 
  • In December, aerators on Oxidation Pond 1 restarted to minimise odours.

March 2024

  • A report on the insurance process and odour mitigation efforts was provided to the Council.
  • Odour mitigation plan released. 
  • Odour mitigation work is underway. Various actions taken to improve plant performance and reduce odour. 
  • A new interactive map was created showing odour mitigation work. 

April 2024

  • Ponds switched to winter operation mode. Adjustments made to our operations to reduce odours when the biology changes as weather cools. 

May 2024

  • The Mayor and councillors approved a grant of $130,000 to resource a project with the goal of strengthening and sustaining effective and respectful relationships with Eastern Communities.
  • Completed work to cover inlet chambers to contain odour. 
  • Completed replacement of the bio-bed material in the odour control system. Old material reused as soil conditioner for native planting areas.

October 2024

  • Christchurch City Council and its insurers have agreed on a settlement in relation to the fire-damaged trickling filters at the Christchurch Wastewater Treatment Plant.
  • The Council also approved the replacement of the trickling filters with an activated sludge reactor.
  • This significant milestone allows us to move forward with building a resilient and more environmentally friendly wastewater treatment plant for our growing city.
  • Replacing the trickling filters with an activated sludge reactor will give the Council the opportunity to significantly reduce greenhouse gas emissions. Additionally, activated sludge reactors can deliver better environmental outcomes and have a smaller footprint that can be cost-effectively upsized to accommodate the needs of our growing population.
  • Design work is underway and it’s expected to take up to three years to complete the design and construction of the new activated sludge reactors.

November 2024

  • Demolition of the Christchurch Wastewater Treatment Plant’s fire-damaged trickling filters started.
  • Southern Demolition is doing the work, which is expected to take four to five months to complete. 
  • The demolition is the first stage of physical work to replace the filters with an activated sludge reactor, which will fix long-standing odour issues. 

December 2024

  • Demolition of the trickling filter walls is complete. Work is now focused on the central columns and foundations. 

November 2021

  • On 1 November 2021, emergency services respond to a fire at the Wastewater Treatment Plant in Bromley. Both of the trickling roof filters collapse. The damage couldn't be assessed properly until the fire was completely out.
  • On 4 November, the Council installed a sprinkler system to remove hot spots and help reduce the smell. We also begin working on an adaptive management plan to figure out the best possible outcome for the discharge of wastewater from the plant.
  • On 26 November, the fire is officially completely extinguished by the fire service. The Council identifies the need to remove the two trickling filters. Both filters store 13,000 cubic metres of material.
  • The Council started using misters and polyaluminium chloride - an odourless powder that dissolves in water - to help suppress the smell. Polydosing also settles more of the suspended solids in the wastewater, improving the water quality as it progresses through the plants.
  • Hydrogen peroxide - a compound that naturally breaks down into water and oxygen – starts to be added to the wastewater before it’s discharged into the oxidation ponds.

December 2021

  • On 6 December, the Council completed a successful trial to remove a section of the fire-damaged media from the plant. This means the Council could begin assessing the stability of the structures.
  • On 17 December, Council staff planned to convert two of the plant’s four clarifier tanks (or secondary contact) into aeration tanks. Installing four aerators in each of the two tanks will help decrease the bad smells and improve the quality of the wastewater being discharged. The Council anticipated that it would be years before the trickling filters could be replaced or rebuilt.

February 2022

  • On 14 February, aeration components begin to arrive to implement the interim plan to minimise odours from the fire-damaged plant.

March 2022

  • On 16 March, eight aerators are installed in two of the plant’s four clarifiers.
  • Soon afterwards, increased odours from the trickling filters are detected after wet weather. It's determined that the acute stench is caused by the material inside the trickling filters rotting and drying out.

April 2022

  • On 6 April, the aerators installed in March are turned on.
  • On 12 April, the Council decided to fast-track the appointment of a contractor to remove the burnt filter material.

May 2022

  • Filter media removal work starts.
  • On 6 May, independent testing to better understand the odours from around the fire-damaged plant detects small amounts of hydrogen sulphide and methyl mercaptan.
  • On 26 May, the Council confirms a community support package for 3,380 of the most affected residents.

June 2022

  • Southern Demolition and Salvage Limited conducted a test run, removing and transporting the burnt trickling filter material on Friday 3 and Saturday 4 June.
  • Work to remove the trickling filter began on 6 June.

July 2022

  • The new activated sludge treatment process becomes fully operational at the plant.
  • This new system pumps wastewater from the converted aeration basins to the clarifiers, which greatly improves the quality of the wastewater.

August 2022

  • Trickling filters are emptied one month ahead of schedule.

September 2022

  • Odours from the oxidation ponds are expected to reduce from September, although it is expected that some odours will remain for most of the month. These will progressively reduce as the pond's health improves.

April 2023

  • A project to increase the biological health of Pond 1 is completed after 16 aerators are installed and turned on, churning more than 300kg of oxygen into the pond every hour.
  • In the long term, these aerators will ensure the entire pond continues to stay healthy and function well.

May 2023

  • The disc aerators on Pond 1 failed and were in the process of getting repaired.

Late 2023

  • Fencing around oxidation ponds was installed to improve safety and reduce rubbish entering ponds. Subsequent minor changes were made to deter birds and improve effectiveness.
  • Insurance negotiations were continuing.
  • In November, a report on the insurance claim for the November 2021 fire was provided to the Council. 
  • In December, aerators on Oxidation Pond 1 restarted to minimise odours.

March 2024

  • A report on the insurance process and odour mitigation efforts was provided to the Council.
  • Odour mitigation plan released. 
  • Odour mitigation work is underway. Various actions taken to improve plant performance and reduce odour. 
  • A new interactive map was created showing odour mitigation work. 

April 2024

  • Ponds switched to winter operation mode. Adjustments made to our operations to reduce odours when the biology changes as weather cools. 

May 2024

  • The Mayor and councillors approved a grant of $130,000 to resource a project with the goal of strengthening and sustaining effective and respectful relationships with Eastern Communities.
  • Completed work to cover inlet chambers to contain odour. 
  • Completed replacement of the bio-bed material in the odour control system. Old material reused as soil conditioner for native planting areas.

October 2024

  • Christchurch City Council and its insurers have agreed on a settlement in relation to the fire-damaged trickling filters at the Christchurch Wastewater Treatment Plant.
  • The Council also approved the replacement of the trickling filters with an activated sludge reactor.
  • This significant milestone allows us to move forward with building a resilient and more environmentally friendly wastewater treatment plant for our growing city.
  • Replacing the trickling filters with an activated sludge reactor will give the Council the opportunity to significantly reduce greenhouse gas emissions. Additionally, activated sludge reactors can deliver better environmental outcomes and have a smaller footprint that can be cost-effectively upsized to accommodate the needs of our growing population.
  • Design work is underway and it’s expected to take up to three years to complete the design and construction of the new activated sludge reactors.

November 2024

  • Demolition of the Christchurch Wastewater Treatment Plant’s fire-damaged trickling filters started.
  • Southern Demolition is doing the work, which is expected to take four to five months to complete. 
  • The demolition is the first stage of physical work to replace the filters with an activated sludge reactor, which will fix long-standing odour issues. 

December 2024

  • Demolition of the trickling filter walls is complete. Work is now focused on the central columns and foundations.