The Queenstown Lakes District Council (QLDC) applied for retrospective resource consent from the Otago Regional Council (ORC) for its emergency measures, but the application has yet to be notified and no hearing date has been set.
When the QLDC began its "short-term solution" on March 31 it said it was discharging about 12,000cum of treated wastewater a day, or the equivalent of just under five Olympic-sized swimming pools.
That was 81 days ago.
The ORC has said under the Resource Management Act its staff need to confirm the application is complete, decide if further information is needed and make a formal notification decision, despite the QLDC’s request the application be publicly notified.
Regular sampling is done so any impacts on the Shotover and Kawarau Rivers can be monitored and the data is publicly available.
But the ORC website confirms "questions have been raised about the impact of the discharge on the Shotover and Kawarau Rivers and what role dilution plays".
"Any decision on if this discharge is appropriate and on effects moving forward will be assessed through any consents and compliance processes."
University of Otago freshwater scientist Associate Prof Marc Schallenberg said the issues raised were interesting, but warned as well the discharge was "risky business".
"This is a very interesting topic," Prof Schallenberg said.
"One of the reasons it is interesting is that almost nothing is known about the ecological health of large rivers like the Kawarau.
"Because it is so difficult to sample large and fast-flowing rivers, we know very little about them."
Typically, assessments were based on water quality without any understanding about the effects on periphyton, invertebrates, or fish.
In a river such as the Kawarau, it seemed these ecological components were of little perceived value due to the nature of the river.
"However, in terms of downstream drinking water use and recreation, the water quality (especially faecal contamination, pharmaceuticals, etc) is quite important."
He said the issue was outside his personal area of expertise, but he supposed the mixing, or dilution, that was happening in the river would be quite rapid and thorough not far downstream from the Shotover confluence.
"I guess that by the time it gets to AJ Hackett [Bungy Centre], the sewage will be quite diluted.
"But the final concentration of contaminants will depend on the concentrations in the effluent and the amount of water available for dilution.
"It’s all a messy, risky business where there are downstream users."
