Details scarce on status of swamp at centre of sewage spill

A quick assessment by the Queenstown Lakes council and a 420,000-litre sewage spill has been declared "contained" by a swamp, but details of the geology of the swamp or its environmental significance are not forthcoming.

The patch of wetland that soaked up the partially treated wastewater on Monday is not part of the 15-hectare Shotover River Confluence Swamp, noted by the regional council for its "remarkable" variety of plants, some of them nationally or internationally rare or threatened species.

However whether it is a named, natural or noteworthy swamp or the nature of the rock or earth it sits within remains unclear.

Acting head of the Otago Regional Council's regulatory team Joanna Gilroy today declined to answer questions from Crux regarding the area impacted by the spill.

"The issue at Shotover plant is still under active investigation by ORC staff and we are unable to comment further until that has been concluded. Any effects on the wetland are also being considered as part of that investigation."

Queenstown Lakes District Council infrastructure and property manager Simon Mason has told Crux today "a visual inspection of the runoff" is what gave the council confidence to issue a statement on Tuesday the spill has been "fully contained within the swamp".

He did not confirm if any external experts - such as geotechnical engineers or environmental scientists - had been consulted prior to the council delivering its statement.

In his written response to follow-up questions from Crux today Mr Mason says an internal investigation is underway to "fully understand" what caused the sewage overflow, which started at 4am on Monday and continued for 12 hours before being stopped.

"Normally, wastewater treated within the oxidation pond system is pumped from the pond and combined with the flow from the activated sludge plant prior to passing through the ultraviolet plant and on to the disposal field.

"The pump station includes two pumps which automatically manage the level within the pond.

"At this stage in our investigation, it appears that this control system failed to automatically respond to an increase in the pond level over the weekend...this does not mean the pumps themselves failed.

"Instrumentation detected a high level which raised an alarm locally but did not page to an operator as we would have expected."

The flow channeled its way overland, under a fence, across a road and into a swampy patch of vegetation beside the Shotover River, with a local walker describing  it to Crux as "absolutely disgusting".

Earlier this week Otago regional councillor Michael Laws challenged the lack of regulatory enforcement shown to the district council, saying he had seen local authorities prosecuted for "much less".

Monday's overflow from an oxidation pond is the latest in what's been a serious of malfunctions over recent months at the QLDC-run wastewater treatment facility.

However ORC compliance boss Tami Sargeant earlier told Crux her team's priority is allowing the QLDC to focus on fixing the problems.

Main image: Partially-treated sewage spills from the Queenstown Lakes District Council's Shotover Wastewater Treatment Plant, Monday, December 15, 2024.