Oxidation ponds all return to green

Following the significant amount of rainfall we've had over the past few weeks, the dissolved oxygen levels in the ponds are the highest they have been all winter, and our visual observations of the ponds show that the water looks clear and lightly loaded.

The last time we received a large rainfall event was before the temporary activated sludge plant was brought online, and based on what we observed at the time, we believe there is only a very low risk of odours for the coming weeks. As a result, we've turned all of our ponds 'green' again in the pond health tracker above.

Yesterday, as part of Council’s routine monitoring, it was found that one of the disc aerators  on Pond 1 wasn't operating. The contractor was notified and they attended site later in the morning, advising that a repair was necessary, but were unable to advise when the aerator was likely to return to service. We don't anticipate that the failure of this single aerator will generate odours.

We've undertaken a survey of the sludge blanket at the bottom of Ponds 1 and 2 to get an understanding of how the ponds are likely to perform in the future and found that the layer of sludge is less than anticipated. This is good news, as it means the ponds' sludge levels are still within normal operating parameters. As a result, the sludge is unlikely to be a future source of odours. 

The independent internal review into the Council's response to the wastewater treatment plant fire is now due to be completed by mid September. The external reviewers have informed us this delay is due to the limited availability of some key stakeholders that they considered essential to interview as part of the review.

We update the webpage below with the latest updates as they come to hand. 

Latest hydrogen sulphide monitor results

We have strategically set up hydrogen sulphide (H₂S) monitors at locations around the oxidation ponds and nearby community. These have been in place since July last year and the results are published on the webpage below.

Since the five disc aerators have been repaired, levels of H₂S have remained low, intermittent, and well below the guideline of 0.03ppm. 

This graph usually also displays readings from Rudds Road, but that data isn't displayed this week. We've been getting low level readings of H₂S from this meter, well below 0.01ppm, but persistent over the whole week.

We're very confident they're not from our ponds as the wind directions do not correspond and we're not detecting H2S closer to the ponds. We're investigating whether there is an issue with the meter at that site or another source of H₂S in the vicinity.

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.