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.