Changes to Ponds 2A and 2B

We’ve noticed that Ponds 2A and 2B are showing signs of changing due to the reducing daylight hours and the very settled weather conditions we have experienced lately.

The biological oxygen demand (BOD5) has slowly been trending upwards while the dissolved oxygen levels are slowly decreasing. We have also noticed a slight visual haze on the surface of the first two oxidation ponds, and a very faint odour when we’re within 10m of the ponds’ edge.

Taking all these indicators into account, we’ve decided to err on the side of caution and turn ponds 2A and 2B back to ‘orange’ in our pond tracker.

An orange reading means the water quality in that specific pond is average and there’s the possibility of odours, especially on very calm and settled days.

What we're doing about this

We have anticipated that the cooler months and reducing sunlight hours could affect the performance of the oxidation ponds and we are working hard to establish a series of 16 mechanical aerators on Pond 1.

These aerators, which we’ve sourced locally and are being manufactured in Rolleston and Timaru, will churn more than 300kg/h of oxygen into the wastewater and improve the biological health of the pond.

We’re currently installing the electrical cabling that’s required for these aerators, and permanent location marker buoys will be installed next week.

Five disc aerators (above left image) – which transfer lots of oxygen to the water while also creating optimum flow patterns in the pond – are on schedule to be installed around the edge of Pond 1 by the end of this month.

An additional 11 vertical shaft aerators (above right), which can push very high levels of oxygen into the water, will begin arriving on site by mid-March. This is the style of aerator we installed on the clarifiers last year, as part of the temporary treatment process.

We’ll begin installing these across Pond 1 by the end of March, and hope to have this work completed in May.

Options around a permanent solution for the fire-damaged wastewater treatment plant will go before the Council once the insurance processes have been settled. This process could take some months.

We’ll keep you updated as this project progresses.

Current hydrogen sulphide readings

This graph displays the hydrogen sulphide (H₂S) results from monitors situated at:

• Rudds Road, which will detect hydrogen sulphide carried on an easterly wind from the direction of the wastewater treatment ponds.
• The Dog Shelter, which is located between Living Earth and the oxidation ponds, which will detect hydrogen sulphide coming from either the ponds or the estuary.
• South New Brighton School, which will detect hydrogen sulphide carried on a west or southwest wind from either the ponds or the estuary.

The graph shows that only low levels of H₂S were detected on a few occasions at the sites. 

We're seeing consistent trends of occasional H₂Sconcentration readings at the sites near the estuary, coinciding with very low wind speeds and typically in the hours after low tide.

You can read the latest data for all locations, and an explanation about how to read the information by clicking the link below. You can also find past readings for each site. 

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 

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.