The ORC asked the Queenstown Lakes District Council (QLDC) for more information to support its claim the effects of the emergency discharge from its Shotover wastewater treatment plant into the river would be "less than minor".
In a letter dated June 19, and published late last week, ORC consents processing planner Hannah Goslin said the QLDC’s retrospective consent application for the discharge relied on "a small amount of monitoring data to support the conclusions reached in terms of the scale and significance of effects".
"It is understood that monitoring is ongoing, and further data will be provided as it becomes available," Ms Goslin said.
"Observations from current monitoring indicates that ammonia concentrations at [five sites] suggests there is potential for the discharge to cause exceedances of the national bottom line for ammonia."
She said "each of these sites" had at least one exceedance of the 95th-percentile in the monitoring record available at the time the QLDC lodged its emergency consent application.
She called for an assessment of the "expected key contaminant concentrations" downstream from the discharge which considered background water quality conditions and low flow scenarios.
The assessment should include assumptions for dilution rates, river flow and discharge volumes.
It should also consider the effects after "full mixing" in the Shotover and Kawarau Rivers, she said.
The ORC was also seeking information on the likely maximum flow rate and the flow’s effect on the braided river’s river bank, the aquatic ecosystem and the river’s natural character.
An initial assessment of the application had been made by the ORC planner and five experts who would complete the technical audit, she said.
The ORC’s request information was published on the council’s website on Thursday, the day before the QLDC asked the ORC for its application to discharge to the river to be heard by the Environment Court rather than at an ORC hearing.
The QLDC used emergency powers and began discharging treated wastewater directly into the river on March 31 as its Shotover treatment plant’s disposal field failed.
The resource consent application to discharge treated effluent to the Shotover River was submitted to the ORC on May 1.
A statement from the QLDC on Friday said if the ORC granted the QLDC’s request for its application to go before the Environment Court, the ORC would still be required to provide an assessment of the application and a report, which would include a summary of public submissions, before the matter was heard by the court.
