Midge numbers remain high

The high number of midges coming from the oxidation ponds continues to impact neighbouring areas. The midges are caused by the healthy conditions of the oxidation ponds and associated algae, which is a food source for midges.

Since the fire at the Wastewater Treatment Plant midge numbers haven’t been a significant issue and we haven’t had to use the techniques we employed before the fire. Carrying out those midge control measures now is risky, as the current health of the ponds is one of the reasons odour has reduced significantly since before the holiday break.

The most effective midge control measures require dredging the ponds or altering the flow path of wastewater. Both these changes to the treatment process could cause a significant increase in odour. In addition to this, odour caused by a change in pond biology takes time to address, and in a worst-case scenario an increase in odour could last until winter. 

The weather has a huge part to play in how our oxidation ponds operate, and the strength of wastewater entering the ponds is now increasing due to a recent patch of reasonably dry weather. If this weather continues it could make the pond conditions less suited to algae, which could in turn result in a decrease in midges.

We know the midges are frustrating and are grateful for the ongoing patience of residents living in impacted areas. When making decisions about next steps we’re balancing odour and midge management to try and get the best result for the community. Our staff continue investigating which control options we might be able to implement and we’re working with external experts to assess the risks, and to ensure that we’re doing what we can. We’re hoping to have this completed early next week.

Trickling filter demolition update

Demolition of the trickling filter foundations is progressing well as seen in the picture below. The centre column of the structure has more concrete and steel than anticipated and will take a bit more time to demolish. This work also generates slightly more noise and vibrations. Our contractor is mindful of this and coordinates the work so that they’re not constantly working on the centre column. Work on the design of the activated sludge reactor continues and we’ll keep you informed of progress.

The photo below was taken on 21 January 2025.  

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.

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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.