Weather conditions leading to increased odours from oxidation ponds

Due to milder conditions and a gentle easterly wind over the past few days, Christchurch City Council has received an increased number of reports of unpleasant odours coming from the oxidation ponds at the wastewater treatment plant.

Head of Three Waters Helen Beaumont says the air quality readings that staff received this morning show increased hydrogen sulphide levels at the monitors set up west of the ponds.

“While the very high rainfall in July flushed the ponds and the westerly winds over the past few weeks have given many Christchurch residents a reprieve from the smells, the biological health of the ponds is still poor,” says Ms Beaumont.

“Generally, the hydrogen sulphide levels we’ve recorded are still below the California Office of Environmental Health Assessment (OEHA) guideline of 0.03 parts per million (ppm), which is the ‘threshold of concern’ for impacts on community well-being.

“However, readings from our Shortland Street monitor, which is close to the ponds, shows that over the past few days nearby residents have been experiencing levels of hydrogen sulphide close to, and sometimes exceeding, the OEHA guideline.

“Despite these increases, we’ve received assurance that we’re still on track for these odours to have significantly reduced by mid-September.”

Ms Beaumont says the new activated sludge treatment process at the plant continues to build a healthy biological base, and this will lead to better-quality wastewater flowing through the ponds over the coming weeks.

“While odours from the ponds will gradually reduce over the coming weeks, it will take another couple of months for the biological health of the ponds to return to a level of resilience where they’re capable of handling increased organic loads if there’s a temporary failure somewhere in the treatment plant process.”

For more information on the wastewater treatment plant recovery visit ccc.govt.nz/wastewaterfire

Latest continuous air monitoring readings