During recent upgrade works there was "some ponding" in the plant’s disposal area and surface run-off from the site, and total nitrogen within treated wastewater had exceeded consent requirements, the Queenstown Lakes District Council said in a statement yesterday.
The Otago Regional Council had been notified immediately and its investigation was under way, it said.
QLDC property and infrastructure general manager Tony Avery said the situation facing Project Pure Wastewater Treatment Plant was unfortunate and would be unwelcome to many.
"We’ve been busy working to improve both the efficiency and resilience of Project Pure by replacing aeration equipment in two older reactor tanks on site, an activity made possible by construction of the facility’s third reactor completed early 2024," Mr Avery said.
"There was always a risk that some parts of the facility’s treatment process would be negatively impacted while carrying out these significant upgrades.
"To reduce as much risk as possible, works were carefully planned to take place during low flow periods and operational teams implemented several mitigation strategies."
The upgrades at the treatment plant involved taking one of the older reactors offline for "inspection and upgrades", while the other two reactors remained functional.
Once complete, the first reactor was returned to operation before the second older reactor was taken offline.
The first upgrade was successfully completed in July this year, and the plant operated on three reactors for a period of time to confirm functionality before work began on the second reactor.
However, while that work was under way, increased flows from winter school holidays and heavy rain put strain on the facility’s biological treatment process.
"This led to treated wastewater exceeding the consent requirement for total nitrogen (an 80th percentile of 12mg/litre), periods where surface ponding occurred across the facility’s disposal fields and surface run-off from the site during heavy rain at the end of October," the QLDC statement said.
Mr Avery said he acknowledged ponding within Project Pure’s disposal fields would trigger comparisons to recent issues at the Shotover wastewater treatment plant, but the two disposal solutions were different from each other, and no long-term problems were expected in this case.
"Project Pure’s fields have been operating successfully for approximately 15 years now, have more modest loading rates and discharge through free-draining soils well above groundwater," Mr Avery said.
"We are investigating the effects of the recent events on the disposal fields and will keep the community informed as we learn more about any remediation activities required.
"With upgrades now complete at Project Pure and all three reactors operating, we’re already seeing the quality of treated wastewater improving despite biological processes needing several weeks to stabilise.”
ORC compliance manager Simon Wilson said yesterday the regional council’s investigation was in its final stages, and it was expected to be closed this week.
"There is no evidence that the discharge entered any creek, stream or river," Mr Wilson said.
He said the regional council took its role as a regulator seriously "and compliance from consent holders is expected".
Mr Wilson said the plant was issued with an infringement notice two years ago. — Allied Media
