Shotover Wastewater Treatment Plant upgrades

What is happening?

We're planning to build a treated wastewater calamity pond, which will provide temporary storage during unexpected events or disruptions.

Before construction can begin, the existing treatment ponds need to be decommissioned. This means removing water from the ponds and allowing the remaining wastewater sludge to dry within the existing pond area. Any water removed from the ponds will be processed through the treatment plant and treated before it is discharged to the environment.

When will work take place?

Work will be underway from November 2026. Sludge dries most effectively during the warmest and driest months, when evaporation rates are highest and the risk of rainfall is lowest. In Queenstown, the best conditions for natural drying are typically from November to March. Depending on weather conditions, the drying process is expected to continue through the first half of 2027.

What might I notice?

During the drying process, there may be occasional odour from the site. Significant odour effects are not expected, but people nearby may notice odour from time to time.

Any odour will depend on weather conditions, including temperature, wind direction, and rainfall. Odour is more likely after periods of significant rain.

How will odour be managed?

QLDC will work with the contractor to prepare an odour management plan before the works begin.

This is expected to include:

• Regular odour monitoring during the works.

• Applying lime if elevated odour levels are detected. Lime helps reduce odours by raising the pH of wastewater and sludge, which suppresses the formation and release of odorous gases such as hydrogen sulphide.

• Deployment of additional odour suppression measures, if required.

Site conditions will be monitored throughout the project so any required mitigation measures can be put in place quickly.

What material is being dried on site and what will happen to it?

The material being dried is wastewater sludge that has built up at the bottom of the oxidation ponds over many years as part of the normal wastewater treatment process. It is made up of organic matter and contains a high proportion of water.

During the decommissioning works, the sludge will be left to dry within the existing pond area to reduce its moisture content. Once dry, it will be consolidated and safely contained in a designated part of the pond site. It will then be covered with gravel. 

What will happen to the site once the pond decommissioning works are complete?

Once the ponds have been dewatered and the remaining material has been dried and consolidated, construction of the treated wastewater calamity pond will begin.

What is a treated wastewater calamity pond?

A treated wastewater calamity pond is an important resilience measure for the wastewater treatment plant. It provides temporary storage for treated wastewater if normal operations are disrupted, for example by a power outage, equipment failure, or maintenance issue.

Based on average daily wastewater flows, the pond is designed to provide up to 48 hours of temporary storage. This gives operators time to respond to an issue and restore normal operations.

The calamity pond is part of QLDC’s wider programme to improve the resilience and reliability of wastewater infrastructure. It will be operational by the end of 2027.