Christchurch Wastewater Treatment Plant update

Thursday 19 February 

This morning's odour 

We know that the odour was particularly noticeable for a period this morning, and this was picked up on some of our odour monitors. We’re sorry for the disruption this may have caused.

While we had taken steps to manage the impact of the recent rainfall event, these situations are unpredictable and we knew some odour was possible. Weather conditions have since improved, and the odour has largely subsided.

Odour levels can change quickly, particularly with shifts in weather and other environmental factors. We are continuing to closely monitor the situation and will keep the community updated as soon as we can if there are any further changes.

When we’ll be in touch again

Unless conditions change significantly, we’ll be back in touch on Monday with another update, including the next round of hydrogen sulphide graphs. 

 Community outreach – introducing Gary Watson 

My name is Gary Watson, I’m working alongside the local Councillors and Community Board to support good information flow and to look at ways to help make living in the area as positive as it can be while the plant is rebuilt.

I’ve been in community roles at Christchurch City Council since 1999. I delivered the social response in May 2022, meeting many of the affected community over that time.

I intend to be based in your community to be as accessible as possible. It will take me a little time to get things in place, but I will be at the Bromley fair on Saturday cooking the barbeque if you are interested in a chat.

My contact details at this stage are gary.watson@ccc.govt.nz but once I have found a base I will share that address and a phone number with you.

Odour status 

The recent storm and then more settled weather conditions over the last 36 hours have seen an increase in odour from the ponds for a period this morning and a change in our odour assessment, with a higher probability of odour from some of the ponds.

Although Pond 2A has high algae concentration, the results of dissolved oxygen were low and there is low algae concentration in Pond 5 and 6.

Staff are monitoring the odour and making changes where possible. We’re continuing hydrogen peroxide dosing and all of our aerators are operating.

An algal expert has assessed the health of the algae in the ponds and provided a detailed report – read more on that below.

Activity on site

The team is well into excavation for the activated sludge reactor – we have excavated 3200m3 of sand, enough to build about 1 million medium-sized sandcastles. Next week, they will start installing sheet piling to support the existing structure and enable the excavation next to it.

Here’s what you need to know about noise, dust and traffic management:

• Noise and vibration is monitored at the site boundary, with strict limits in place. If these limits are exceeded, mitigation measures will be put in place.
• Dust control includes visual monitoring, water carts, speed limits, and other suppression techniques to keep dust to a minimum.
• Traffic management is in place to reduce impacts on the community. 

Work hours will be Monday to Saturday, 7.30am to 6pm. If any work needs to happen outside these hours, we'll notify the community in advance. 

Latest hydrogen sulphide monitoring 

The latest hydrogen sulphide graph shows that H₂S remains present at detectable levels. Our teams will continue to monitor readings closely and provide updates as trends develop.

Algae expert on the ground

An algae specialist visited the ponds last week to help us understand how the ponds are recovering. Algae are a key indicator of pond health – different types show up as conditions improve, so looking at what’s growing helps us track how each pond is doing.

Overall, the specialist found that all seven ponds look healthier than they did in early February when the stench was at its worst. We’re now seeing more of the “good” algae that usually appear in well‑functioning ponds. These early algae help improve the water so more species can return over time.

Pond 1 is still the least healthy, with fewer algae types and more bacteria than we want to see. But even there, we’re starting to notice small signs of improvement.

The other ponds showed good progress, with a mix of healthy green algae and, in some ponds, tiny invertebrates. These are normal in ponds that have good oxygen levels and are treating wastewater well.

We’ll keep checking algae regularly. It’s one of the key tools helping us understand how the ponds are recovering and what to expect as conditions continue to improve.

Smelt it? Log it.

If you notice an odour, the best way to report it is by visiting smelt-it.web.app and logging what you’re experiencing – including location and strength. These reports help us build a fuller, more accurate picture of what’s happening across the community, so we can continue working to improve conditions.

Stay updated

We want everyone to be able to stay updated on what's happening at the Christchurch Wastewater Treatment Plant, and we regularly post new information 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.