Two ponds go green, two more turn orange

Now that the new activated sludge system is allowing better-quality wastewater to flow through the oxidation ponds, the health of the ponds is starting to recover at a faster rate.

This week we're excited to let you know that ponds 5 and 6 have reached our benchmarks for biological oxygen demand (BOD5) and dissolved oxygen, and we've turned them 'green' on our pond health tracker above. 

A 'green' indication means the biological health of these ponds has improved to a point where they’re capable of handling increased organic loads if there’s a temporary equipment failure somewhere in the treatment plant process.

At the same time, we've seen noticeable improvements in ponds 3 and 4. They've now reached the thresholds we've set for dissolved oxygen and BOD5, and we're able to now turn them 'orange'.

Waterfowl returns to the ponds

The Council's ecologist and our wastewater treatment plant operations team have reported an increase in the number of birds - and their main food source, midges - at the ponds over the past couple of weeks.

A member of the operations team snapped the above image of two adult black swans and their four cygnets on one of our ponds earlier this week.

Our ecologist  undertook a bird life survey of the oxidation ponds over the weekend and recorded more than 1,000 waterfowl present.

Noticeable drop in recorded hydrogen sulphide levels

Every Wednesday we upload the past week's data for the continuous air monitors that have been set up near the Christchurch Wastewater Treatment plant.

The monitors are to detect the levels of hydrogen sulphide in the Shortland Street and Rudds Road areas, as well as at Bromley and South Brighton Schools.

Over the past week we've noticed a significant drop in hydrogen sulphide levels across all sites, helped by both the improving oxidation pond health, and the stronger spring winds that have helped dissipate the odours more quickly.

 Note the readings online are only up until Friday 16 September – we'll publish graphs showing this week's increased levels of hydrogen sulphide early next week once the data from all of the sites has been collated.

You can read the 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 in advance for your patience and understanding as we continue to work on minimising the unpleasant smells after the fire. We’ll be in touch again soon.