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

New interactive map

28 March 2024.

We’ve produced an interactive map(external link) that shows what we’ve got planned or underway to address odour at the Wastewater Treatment Plant. Selecting any of the hot spots on the map will show you a description of what work is being done to address odour at each source.

We’ll keep this map and webpage up-to-date as our work changes.

Upcoming community board presentation

28 March 2024

On Monday 8 April, Wastewater Treatment Plant Operations Manager Adam Twose is presenting to the Waitai Coastal-Burwood-Linwood Community Board. He’ll give an update on the latest actions underway and our plans for the next few months.

This meeting will be live-streamed on the Council live website(external link) and is open to the public.

Two aerators out of service

28 March 2024.

A vertical shaft aerator and disc aerator went unexpectedly out of service over the weekend. The vertical shaft aerator went down following damage and needs to be replaced with one of our critical spares that the contractor keeps available for instances like this. The disc aerator has minor damage and needs to be removed and repaired. Both aerators are expected to be back in service on Friday 5 April.  

At this stage, the loss of two aerators isn’t having an effect on the oxidation ponds. Fourteen aerators remain in service and forecast wind conditions are good for dispersing any additional odour in the short term.

Transition to winter mode

28 March 2024.

We have a plan to minimise the odour from the ponds, which could occur


Odour mitigation work underway

18 March 2024

We recently submitted an odour mitigation plan(external link) to Environment Canterbury in response to issues raised in a Compliance Monitoring Report.

The plan outlines the many actions we’re taking to address odour at the Christchurch Wastewater Treatment Plant to address the issues, improve the performance of the plant and lessen the impact on the community.

We’ve provided an update below on some of the key actions currently underway at parts of the plant. We’ll continue to provide updates on this work and any additional actions that happen in future.

Screen room – a temporary ventilation system has been installed in the screen room and consultants are looking into a permanent system.

Primary settlement tanks – this is where the majority of odour is coming from and we have a range of work underway to improve their performance:

  • We’ve reduced the number of tanks in service to move sewage through the system more quickly. Following an electrical failure we had to return one tank to service. We intend to get back down to four tanks as soon as possible.
  • We’re doing manual daily scum removal.
  • We’ve engaged a contractor to investigate the possibility of a containment system to address odour.
  • We’re investigating covering chambers where there is significant surface disturbance.
  • We’re investigating improving the automatic water spray scum removal system.

Temporary secondary treatment – a consultant is working over 18 weeks to improve this phase of treatment.

Odour control system – we have three bio-bed systems to address odour. We’ve rewired the system to get more fans working and are doing more proactive maintenance. We’re engaging a contractor to renew the remaining bed media.

Oxidation ponds – all aerators are in service and expected to remain so. On 8 March we briefly turned all aerators off to carry out critical maintenance work. This went well and didn’t cause additional odour. There is no further planned maintenance coming up and all aerators are available as we head into winter.

Digesters – investigations revealed the pipework is slightly too small. A project is in the final stages to upsize this. We’re also doing more proactive maintenance.

Odour monitoring – the intensive odour monitoring service is underway and continuing beyond the initial four weeks.

Transition to winter  we’ve developed a plan to minimise the odour from the ponds during the summer to winter transition. This is being checked over the next week and will be put in place by the end of the month.

Website changes – we’re working on making changes to our website so it’s easy to see what odour mitigation work is underway. We expect this to be available in the next week or so.
 


Odour mitigation plan published

11 March 2024

 An odour mitigation plan for the Wastewater Treatment Plant has been released by Christchurch City Council.

The plan was produced in response to issues raised in a Compliance Monitoring Report from Environment Canterbury, following reports of odour in areas close to the plant.

You can read the plan here [PDF, 3.4 MB] or find out more on Newsline(external link).


Update on odour mitigation 

1 March 2024

An update report(external link) regarding the insurance process for the Christchurch Wastewater Treatment Plant was received by Council at the Finance and Performance Committee meeting on Wednesday 28 February.

The report contains all the information that can be released at this stage to keep the public informed without prejudicing our ongoing insurance claim or disclosing confidential commercial arrangements. The report confirms that design work to restore the trickling filters is underway and progressing well. Design work is due to be complete within the next two months.

At the meeting the Council acknowledged the community is continuing to experience odours from the Wastewater Treatment Plant. Our staff continue to address the recent increase in odour through a number of actions.   

The primary settlement tanks at the plant were previously identified as one of the main contributors of odour. To address this, we’ve now reduced the number of tanks in service from seven to five. As a result, sewage is now spending less time in in the tanks before it moves to the next stage of the treatment process. Early indications show this has reduced the odour from this source, and we’re planning on taking another tank out of service next week to improve things further.

Our external odour-specialist consultant is making good progress with their intensive odour monitoring programme and they’ve made a small number of recommendations for us to implement.

The trial at the temporary activated sludge plant is underway and being closely monitored to see if the addition of another aeration lane improves the performance of the temporary plant. It will take more time for us to assess if this has any benefits.

The oxidation ponds continue to operate well. Pond #1 now has all 16 aerators back in service. At some stage next week maintenance work requires us to briefly turn off all 16 aerators. We expect they’ll only need to be off for a couple of hours and we’ll plan this for a time where wind conditions are favourable for maintaining  the aeration of the ponds without assistance.


How we're addressing recent odour 

22 February 2024

We’ve worked with the operations team to put together the update below on what’s been causing the recent odour and the steps we’re taking to address it. Our staff are doing all they can to tweak operations at the plant when unexpected odours arise. Operating the plant in its damaged state is an ongoing challenge and we’re doing the best we can to solve problems as quickly as possible.

Our recent monitoring has shown that the odour is coming from the primary settlement tanks at the Christchurch Wastewater Treatment Plant. The tanks are one of the key processes for treating sewage as it comes into the plant. There are seven tanks, which hold incoming sewage allowing the sludge in the sewage to settle to the bottom of the tanks. The sludge then goes to the plant’s sludge digesters for treatment.

The primary settlement tanks have underperformed over the summer and have been identified as one of the main contributors of odour. We are taking measures to improve the performance of the tanks by reducing the number in service. By doing this we’re reducing the amount of time sewage is held in the tanks, which reduces the odour being emitted by them.

At the same time, we’re having conversations with suppliers of odour suppression equipment to assess whether that would help tackle any odours that arise from the tanks.

An external odour-specialist consultant is now halfway through their intensive odour monitoring survey of the plant, and site staff are using this information to make real-time operational decisions on site to try and reduce the odour.

At the temporary activated sludge plant, we’re trialling the addition of another aeration lane. The trial will help us understand if increasing the amount of aeration in this phase of the process makes a difference to the performance of the temporary plant. We’ll be closely monitoring this over the course of the next month to assess any benefits.

The oxidation ponds continue to operate well. Pond #1 now has 15 of the 16 aerators back in service. One of the vertical shaft aerators is being removed and taken to the workshop for servicing, with an anticipated return date of mid-to-late-March. Staggering maintenance of the aerators is important as it improves the resilience of the plant and reduces the chance of multiple aerators being out of service at any one time.


Intensive odour monitoring underway

16 February 2024

We’re one week into an intensive odour monitoring programme focused on the Christchurch Wastewater Treatment Plant itself rather than the oxidation ponds. This will help us better determine the source of recent odour from the plant. This monitoring programme will continue for another three to four weeks.

The initial results from the odour survey show odour is due to the underperformance of the primary settlement tanks. We’re working to address this issue by optimising the performance the tanks, which should reduce odour from this source.

In terms of the oxidation ponds, we are detecting intermittent odour from Oxidation Pond #1. We’re continuing work with the contractor to get all the pond aerators back into service. Three of the eleven vertical shaft aerators are currently out of service, but one is due to be back before the end of the week. We expect all aerators should be back in service by the end of February or early next month.

At this time of year decomposing sea lettuce in the estuary can also be a source of odour, particularly in Ferrymead and coastal areas.


Wastewater Treatment Plant odour 

31 January 2024

Onsite monitoring at the Christchurch Wastewater Treatment Plant shows an increase in odour in recent days. This is backed up by our monitoring stations beyond the site boundary.  

An investigation has identified the odour as coming from the primary settlement tanks, which process wastewater before it enters the temporary activated sludge treatment plant. Our staff are currently in the process of making changes to reduce the odour from these tanks. This is likely to take a couple of days to resolve. We’ve also engaged a consultant who specialises in odour monitoring to assist staff in identifying and responding to odour sources.

There is better news from the oxidation ponds. Our monitoring shows the ponds’ recovery over the holiday period has been maintained, with the majority of the ponds green, and only two still set at their orange setting on the tracker. There are currently 13 of 16 aerators operational, while our contractor works on repairing and returning the other three aerators to service as soon as possible.

We appreciate some of this information is disappointing, and our staff are doing all they can to reduce the odour as quickly as possible.

You can find information about available support on our website.(external link)


Pond health improving 

26 January 2024

Our team has been working hard to operate the wastewater treatment plant and oxidation pond system as effectively as possible.

The overall health of the pond system continues to improve, and the odour has reduced. The temporary activated sludge plant is once again performing well after a phase of instability over the holiday period.

Our air quality monitoring still shows that in certain wind conditions, the plant itself is producing an odour, rather than the ponds. The data also shows that at times ponds #1 and #4 are the source of odour.

While the picture is looking good, we’ve kept oxidation ponds #1 and #4 orange on the pond tracker for now. We’ll keep monitoring the health of the ponds and expect continued improvement.

We’ve got a range of improvement and maintenance work underway. This includes essential maintenance work on three vertical shaft aerators and planning work for a temporary activated sludge plant improvement project.


Treatment plant and oxidation pond performance update

10 January 2024

We’re doing our best to operate the treatment plant in its damaged state, and are continuously making minor changes to improve its performance and keep odours to a minimum.

Our monitoring shows that in certain wind conditions the odour comes from the plant itself, rather than the ponds, and we’re looking at ways we can reduce this.

The oxidation ponds have been operating reasonably well, with H2S levels now at .01ppm. However, during the holiday period the volume and composition of sewage being received at the plant varies significantly and at times the activated sludge plant struggles to adapt, which can lead to occasional odours.

Our contractor is working hard to get two oxidation pond aerators back into service after mechanical breakdowns last year. The contractor is also working through the annual maintenance for all the pond aerators to ensure that they are all available and serviced for the winter period.

We’re making it a priority to explore a permanent solution. For those who might have missed it, an update report on the Christchurch Wastewater Treatment Plant’s insurance claim was provided to councillors in November 2023 – you can find more information and read the report here(external link).


Oxidation pond performance improving

21 December 2023.

We returned the aerators on Oxidation Pond #1 to service about two weeks ago, and it’s already making a positive difference to the biological health of the pond system. The odour coming from the ponds has reduced, as reflected in our monitoring, which shows hydrogen sulphide levels trending down.

Monitoring by both wastewater treatment plant operations staff and contractors shows dissolved oxygen levels are improving, the ponds are looking healthier and algae is returning.

All this means the ponds are now in a healthier state as we head into the holiday period, and we’re able to upgrade the ponds to mostly green on the pond tracker. Unless any new issues come up, we expect odour to gradually reduce even more over the next couple of weeks.

An underlying risk of odours being present around the wastewater treatment plant remains until the permanent solution for the treatment process is completed. Odours can be influenced by unexpected issues arising and weather conditions including temperature and wind.

To reduce the chance of odour over the holiday period, we’ll have 15 of our 16 aerators operating throughout. We also have staff and contractors working through this time.


Oxidation pond performance update

11 December 2023.

The activated sludge plant is not operating as effectively as it should be. This is having an impact on how the ponds are performing, resulting in odours from Pond 1.

Our analysis shows the sludge plant is struggling to cope with the change in weather conditions as we move into summer. All available aerators on Oxidation Pond 1 are turned on to help minimise odours and we’re taking several other actions to improve the sludge plant’s performance, including re-establishing a Compliance Recovery Action Plan.

We have a range of other work underway to improve the overall performance of the treatment plant including repairing an intermittent fault in one of the clarifiers.


Aerators re-started to manage odours 

4 December 2023.

All available aerators on Oxidation Pond 1 have been re-started to minimise odours from the ponds. This decision was made following reports of odours in the area and monitoring showing reduced pond health.  

There may be some increased odour this afternoon as the aerators restart which will stir up the ponds. This should be short-lived, as there are winds forecast for tomorrow afternoon, which will further help rebalance pond health and minimise odours.

The aerators will ensure the ponds continue to stay healthy and function well.


The oxidation ponds are back to green

24 November 2023.

With summer on our doorstep, the ponds are showing signs of being very healthy. Our ongoing monitoring shows that Pond 1, the only one which was still classed as orange, now meets the criteria to finally turn green.

This also means that we're able to turn off several aerators, and we'll monitor the situation to see if they need to be re-started.

This also allows the contractor to do some regular maintenance over the summer period. This will involve bringing the aerators to the shore and taking them away for a service. We'll reinstate them back onto the ponds ready for autumn. 

We've also started the midge monitoring programme. Midge numbers are currently low, which reflects how well-established our midge control measures are, which we've progressively brought in since 2017. We'll continue to monitor the midge numbers, and bring in extra midge control measures if required. 


Insurance update

16 November 2023.

An update report on the Christchurch Wastewater Treatment Plant’s insurance claim for the November 2021 fire on the trickling filters has been provided to councillors. Read the full report.(external link)

The November 2021 fire was an unprecedented event that caused significant damage to two trickling filters at the Plant.

An update report regarding the insurance process, including investigations and the current position, was considered at yesterday's Finance and Performance Committee meeting (Wednesday 22 November).

This report contains all the information that can be released at this stage to keep the public informed without prejudicing our ongoing insurance claim or disclosing confidential commercial arrangements. Read more on Newsline.(external link)


Latest update

30 October 2023.

Two of the vertical shaft aerators on Pond 1 have stopped running. The contractor is aware of the issue, but the windy conditions mean they're unable to inspect and repair the aerators until Wednesday when the wind is forecast to drop. 

At the same time the current windy conditions, and warmer, longer days mean the ponds remain in good health, and we don’t expect the aerator break-downs will result in the ponds producing odours.

The remaining 14 aerators on the pond continue to operate.

On the night of Tuesday 2 October 2023, the arms of one of our two clarifiers at the wastewater treatment plant stopped rotating and were out of action for several hours.

These arms sweep the activated sludge off the bottom of the tank, and play a vital part in the treatment process - our temporary activated sludge plant requires both clarifiers to be running to achieve the current maximum flow through the plant.

Divers found three pieces of rubbish at the bottom of the tank, and since these have been removed, the clarifier arm has continued working. 

The findings of an independent review into the Council’s response and recovery from the wastewater treatment plant fire, and the Council's draft improvement plan, have also just been published with the Council's agenda for next week.  

The review highlights aspects where the Council did well and provides recommendations and suggestions where the Council could improve so that it’s better prepared to face other significant events in the future.

The draft improvement action plan identifies the need to work collaboratively with the local community, key partners and the local Waitai Coastal-Burwood-Linwood Community Board.

Read the Council report(external link) or independent review [PDF, 750 KB].


An update on the oxidation ponds

30 May 2023.

We've updated our situation(external link) page with an update on the oxidation ponds and the odours that are starting to get emitted from them as we head into the cooler winter period. We’re still trying to determine exactly what’s causing the smell, but we believe a combination of factors might be at play.

These include mechanical issues on the disc aerators, algae reducing considerably over the winter months, recent wet weather, and below-average settling floc earlier in the treatment process. Read more about each of these, and what our next steps are.(external link)


A return to all 'green' ponds

20 April 2023.

The 16 aerators we have installed on Oxidation Pond #1 are already making a significant difference to the biological health of the pond system. The aerator's performance is also exceeding the strict design criteria set by the Council staff.

Monitoring by both wastewater treatment plant operations staff and contractors is showing that all ponds are now recording higher dissolved oxygen levels, and visual observations are showing the ponds look healthier.

Observations of the aerators have also shown the initial sludge disturbance has settled down quicker than anticipated, with the water being aerated by the aerators running clear, with no ongoing sludge disturbance.

This has resulted in a negligible level of odours and hydrogen sulphide now being emitted by the ponds; recent monitoring had shown these levels were slowly beginning to increase over recent months.

All this means the ponds are now in a much healthier, robust position as we head into winter, and we’re able to turn all ponds to ‘green’ in the pond tracker(external link).

This rapid response in pond health, and the additional performance provided by the aerators, means the systems we’ve installed are more resilient, and the future risk of odours is now reduced compared to previous forecasts.

However, there will continue to be an underlying risk of odours present around the wastewater treatment plant until the permanent solution for the treatment process is completed.


Oxidation pond aerators are fully operational

 14 April 2023.

A project to minimise odours coming from the Christchurch wastewater treatment plant oxidation ponds has been successfully completed, with all 16 aerators surging to life yesterday. Read more on Newsline.(external link)


FENZ fire investigation report published

16 December 2022.

We have just received from FENZ their Fire Investigation Report – Shuttle Drive, Bromley, Christchurch City [PDF, 5.1 MB].

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 has 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.

The Ministry of Health(external link) has more information about lead-based paint.

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.

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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.