Thursday 23 July 

Christchurch Wastewater Treatment Plant update

All the stone columns are in! 

We have successfully finished installing the stone columns, marking the end of a key ground improvement stage and bringing us closer to construction of the new plant.

The next phase is now underway, with the removal of the crane pad that was used during the stone column installation. Once this work is complete, we will begin constructing the load transfer platform. This is an engineered stable platform, which the new plant will be constructed on. 

Construction of the load transfer platform starts on Monday. During this stage, there will be a steady flow of trucks delivering gravel to site, and two large rollers will be operating throughout the day. This work will generate some vibration, which we will monitor closely to ensure it remains within agreed limits.

Thank you for your continued patience and support as we complete this important preparatory work.

Stage two of aerator project on track 

Our team has been busy getting the infrastructure in place so we can install the remaining aerators and get everything running on electricity. 

To date, we have installed approximately 6km metres of ducting, completed around 1km of trenching, and laid 4km of cabling for power connections. 

The project remains on track, with the new switchboard expected to be completed by the end of August.

Looking ahead, installation of the remaining 13 horizontal aerators is scheduled to begin at the end of August. Once the container and switchboard have been installed and commissioned, the permanent power connection is expected in early September, with the full automated system scheduled to be operational by mid September.

Planned maintenance for digesters 

As part of our ongoing asset renewal and maintenance programme we'll soon begin a major inspection and maintenance project on Digester 1. 

From September 2026, we'll temporarily take Digester 1 out of service so we can empty, clean, inspect and maintain it. This work will allow specialist teams to safely assess the condition of the digester's internal structures and roof, helping ensure the asset continues to operate safely and reliably for years to come.

This type of work is a normal part of operating and maintaining wastewater treatment infrastructure. While the community may notice increased activity at the treatment plant during this period, we have carefully planned the work to support the long-term performance, resilience and safety of the facility.

Digester 1 is one of four low-temperature digesters at the plant. The remaining three digesters have sufficient capacity to continue providing a high level of service to the community while the work is underway. 

The digesters are an important part of the process as they have bacteria which break down the sludge to form biosolids. 

What this work will involve 

Taking a digester offline is a gradual process that can take one to two months. During this time, the system cools down and biological activity comes to a stop.

We will then begin the clean-out and inspection phase, which is expected to take several months. The work involves emptying the digester, removing accumulated material, making the structure safe to enter and carrying out detailed inspections of key components.

Once inspections are complete, we'll confirm whether any repair or renewal work is needed to extend the digester's service life and then carry out any required maintenance.

The overall project is expected to take between six months and one year, depending on the scope of any maintenance work identified during the inspection.

This work will help ensure the plant continues to provide reliable wastewater treatment services for our community into the future.

Pond health, odour and what to expect this weekend 

The oxidation ponds continue to show encouraging signs of good biological health, with dissolved oxygen levels remaining consistently high across the pond system. This shows our recent flow changes have taken effect. As with any natural biological system, some variation between individual ponds is expected and continues to be closely monitored by staff.

Algae levels also remain higher than would typically be expected at this time of year, which is another indicator of strong biological activity within the ponds. The ongoing period of sunny weather is likely contributing to these conditions.

One aerator in Pond 1 is currently out of service. Our contractor is investigating the cause of the fault and working to return the equipment to operation as soon as possible. The remaining aeration systems continue to support the overall health of the pond network.

Stay updated

We want everyone to be able to stay updated on what's happening at the Christchurch Wastewater Treatment Plant, and we regularly post new information on ccc.govt.nz/wastewaterfire 

You're welcome to send this update to your networks. If you know someone in the community who doesn’t have email or internet access, please print this newsletter off and pass it to them.

If you know of anyone who would like to receive this e-newsletter they can subscribe online. 

If you have any questions, or would like further information on the project, please call us on 03 941 8999 or 0800 800 169 or email wastewater@ccc.govt.nz  

Thanks for your patience and understanding. We’ll be in touch again soon.