Christchurch Wastewater Treatment Plant update

22 May 2024

Planting around the oxidation ponds

People travelling along Breezes Road and Dyers Road (SH74) may have noticed our contractors busy planting at a number of locations in the oxidation pond paddocks. We’re taking full advantage of the planting season to give the plants the best chance of establishing and surviving.

This year we are planting approximately 45,000 plants in the paddocks, all of which are eco-sourced natives and selected for their suitability for the local Canterbury environment. We usually only plant around 10,000 native plants a year, but this year we had a very generous donation of 20,000 native plants from Eco Action which has helped us bump up the numbers.

The native plants are primarily being planted to create a natural vegetation barrier to encourage the midges, from the ponds, to remain near the ponds, and not to travel off-site and become a nuisance for neighbours.

Odour control system upgrade complete

In the last newsletter update, we advised that the replacement of the odour control system's bio-bed material was completed. Monitoring by site staff has shown that the odour control system is operating well and performing as required. This is also reflected in regular onsite odour monitoring being undertaken by a consultant.

The bio-bed material, made up of bark and seashells, makes a highly effective soil conditioner, and we’re making use of this in the area surrounding the ponds and in the native planting we’ve mentioned above.

Work on drains around the oxidation ponds

People driving around the ponds might also have noticed some activity at the drains which run around the ponds, namely some minor vegetation removal to enable access for our surveyors. We have a project underway to review the drains and ensure that they are preforming as required. This initial work is to collect all the necessary data to inform the next steps of the project.

Oxidation pond aerators

The contractor has been undertaking their regular maintenance checks on the aerators over the past week. On Tuesday 14 May they isolated each of the 16 aerators to check them over. Fifteen aerators were found to be ok, but one was found to have a broken shaft. This was removed on Thursday 16 May and will be repaired by the contractor, who will investigate the issue and advise when the aerator can be returned to service.

Ponds operating in winter mode

We're still operating the oxidation ponds in the summer to winter transition mode in an effort to reduce odours which were experienced during the same transition last year. This involves directing wastewater past the oxidation ponds nearest residential properties. This reduces the retention time within the pond system more quickly, which should reduce the duration and intensity of any odour event.

We won't know if this approach is successful until the biology of the ponds changes. We're keeping a close eye on the ponds and will be monitoring to see if the changes are effective in reducing odour.

Last year the oxidation ponds started to transition at the end of April, whereas this year monitoring is showing that he ponds are still operating in summer mode. Whilst the temperature of the ponds is slowly declining, there are still high level of algae and associated high oxygen levels.

The image below shows temperature trends for oxidations ponds 1 and 2.

Hydrogen sulphide monitor results

We are continuing to monitor levels of hydrogen sulphide at residential locations around the wastewater treatment plant. Monitoring results have shown that levels over the past month have been decreasing and are now well below the health guideline of 0.03ppm. At times light winds still carry hydrogen sulphide, and other odours, to nearby residential areas but the levels are below 0.01pmm.

Where to get help

If you need health support, we have information available on our website. This includes information on Pegasus Health's Partnership Community Workers and contact numbers for Healthline and counselling services.

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.