Concern over chemicals in mass sewage discharges into Shotover River

Katie Todd, Otago/Southland reporter

Wastewater being discharged into Queenstown's Shotover River could breach national ammonia limits, Otago Regional Council says.

In March, the Queenstown Lakes District Council (QLDC) used emergency powers to begin pumping treated effluent into the river each day from its wastewater treatment plant - the equivalent of nearly five Olympic-sized swimming pools a day.

It retrospectively applied for consent in May, then last week applied for the case to be handled by the Environment Court.

However, a letter now published online shows Otago Regional Council (ORC) had already assessed the application, and placed it on hold due to several concerns.

In the letter dated 19 June, Consents Processing Planner Hannah Goslin said QLDC needed to provide more evidence to support its claim the discharge would have "less than minor" impacts.

"The application relies on a small amount of monitoring data to support the conclusions reached in terms of the scale and significance of effects," she said.

ORC raised concerns about ammonia and phosphorus concentrations observed in the river.

It said monitoring at five sites suggested "potential for the discharge to cause exceedances of the national bottom line for ammonia", and it asked why QLDC had not set a discharge quality limit for phosphorus.

It said QLDC claimed the river would dilute the treated wastewater by 15 to 25 times - but had not backed that up with any hydraulic modelling, dye tests, or flow calculations.

ORC also wanted more evidence to support QLDC's claim there was an initial "flush" of germs when the discharge began.

It also called for a public health risk assessment to evaluate the likelihood of illness from disease-causing microorganisms in the treated wastewater - particularly given the river's "suitability for bathing."

ORC gave QLDC until 11 July to respond to its letter.

"If the information you provide raises more questions, your application will remain on hold until sufficient information has been provided to enable processing to continue," Goslin said.

On Friday, QLDC said the Environment Court was already familiar with the Shotover discharge situation and "would help to provide an efficient and comprehensive decision from a neutral arbiter."

However, ORC would still oversee public notification, submission timeframes, and the technical assessment of the application, it said.

RNZ has approached QLDC and ORC for comment.