The odours reported are the result of three of our aerators failing at the same time.

Repairs have been made to our aerators and they are now working again on Pond Three.

One had an electrical fault, which has been repaired. Another had a mechanical fault, which has had a temporary fix ahead of a permanent replacement.

The third had been clogged by rags and items flushed into the wastewater system.

The odour is dissipating, and any residual smells through town should disappear over the weekend.

We thank our community for alerting us to the problem and for their patience as we worked through the issue.

One of the issues we’re looking to address in its Long-Term Plan is the outdated equipment at our wastewater treatment plant. The potential proposed upgrades will address foul air treatment. The draft LTP will be available to the public from 22 March as part of the Ordinary Council Meeting agenda for 27 March.


We have received service requests regarding odour coming from the wastewater treatment plant. Here’s a rundown of the situation, what we’re doing, and what you can please do to help.


What’s happened?

Our three ponds rely on a fine balance of biochemistry to stop bad odours from travelling most of the time in waste stabilisation ponds. There are two distinct layers within ponds, anaerobic (no oxygen) bottom layer and aerobic (top layer).

The lower layer is made of solids that accumulate over time in the bottom of each pond, where they are slowly consumed by microbes. These microbes produce bad odours which are consumed as they pass through the aerobic layer.

However, if that balance is removed by weather changes, chemicals, or high loads in the network, it will impact the ponds upsetting the aerobic layer and allowing the bad odours to get to the surface.

Pond Three of the wastewater treatment plant [please note – not the new reservoirs] has three aerators, but each has failed. Pond Three is usually the most reliable, but the concurrent failure of three separate aerators is unexpected.


What are we doing?

We are looking for replacement aerators. One is at the end of its life, and our team has been working on a replacement for the last month to get a replacement. A second aerator has a fault, and we are waiting for an electrician to check it. The final aerator stopped this week.

We are investigating today [Friday] as we suspect it is blocked with rags.

We are dosing twice a day in the interim to increase the oxygen level and diverted more of the flow to Pond One.


What can everyone do?

  • Please continue to log service requests at cdc.govt.nz/service-request
  • Please remember the three Ps: Remember the 3 P’s – if it’s not pee, paper, or poo, it doesn’t go down the loo