Christchurch City Council has released an odour mitigation plan for the Wastewater Treatment Plant, in response to a non-compliance report from Environment Canterbury that cited odour complaints from communities close to the plant.

Counci Head of Three Waters Brent Smith said the reasons behind the increased odour issues were because of the “hot and dry summer” which meant the sewage entering the plant was more concentrated and anaerobic.

“When you combine this with hotter temperatures you end up with an increase in odour.”

Smith said an intensive monitoring programme had identified several sources of odour at the plant, and actions were either underway or planned to address them.

One significant source of the odour has been the primary settlement tanks, which have underperformed during the summer.

By reducing the time sewage is held in these tanks, early results have shown a decrease in odour.

Smith acknowledged the community’s stress over the smell saying “the recent increase in smell is a significant cause of stress for the community and we’re committed to doing everything we can to minimise this.”

Maintaining the plant in its current condition poses challenges, including unpredictability, but Smith assured that the team was equipped to handle any issues that arise.

“As we move into winter, the biology of the ponds will change, which is likely to result in a couple of weeks of increased odour.

“We can’t predict exactly when this will happen, but we’ve got a plan ready to go to minimise odour through this period.”