Increase in odour possible

We’re expecting there could be an increase in odour coming from the Christchurch Wastewater Treatment Plant and oxidation ponds in the coming weeks.

A number of factors are influencing the current conditions, including the current patch of dry and warm weather, which has led to more concentrated waste entering the ponds.

This puts pressure on the oxidation ponds, resulting in decreased levels of dissolved oxygen and algae – which may lead to odour.

As always, we’re doing our best to address these issues. Running the damaged plant is a challenge and we’re quick to react when we see changes that could result in odour.

Midge update

We’re still recording midges in large numbers, but for the most part they’re staying around the ponds and not moving into neighbouring areas.

We trialled a midge control method on Pond 2A late last week. This method is called mechanical disturbance, and involves using a jetboat and midge dredge, which disturbs the bottom of the ponds and disrupts the midge lifecycle. Since the trial we’ve been monitoring both midge numbers and odour. We’ve already noticed a drop in pond health since this occurred, which could contribute to an increase in odours.

The midge season could continue until about early April, and in certain weather conditions it’s possible midges will end up in neighbouring areas. 

Staff have reviewed our Midge Control Programme and made recommendations which we are incorporating into our activities. Also based on this report, we’ve now initiated a new combined Midge and Odour Monitoring and Control Project.

The project is in the early stage of design and we’ll provide more details as we can release them. However, we have designated it a high priority project, with an anticipated project completion date of October 2025, in time for the start of the next midge season.

The number of complaints about midges has dropped significantly and we’ve only received one complaint since 24 January

Trickling filter demolition update

Work continues to demolish the activated sludge reactor. We’ve just completed demolition of Trickling Filter 1, including the in-ground structure and central column. This was a challenging aspect of the project as the concrete was incredibly tough. The next stage is removal of the Trickling Filter 2 column. Work is on track and we expect to have both trickling filters entirely demolished by the end of March.

Stay updated

We want everyone to be able to stay updated on our response and recovery from the treatment plant fire, and we regularly post new information and reports 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.