QLDC seals off sewage wasteland that "does not exist."
We background how the failure happened, how its being managed and the impossibility of a quick or cheap fix.
We’ve spent two days this week exploring the largely unseen parts of the Shotover sewage plant just a kilometre away from SH6, the Shotover bridge and the three visible large wastewater ponds that we’ve all seen from the main road.
To be clear, the main wastewater plant has plenty of problems and is near or over capacity. But the immediate crisis affects what was designed to be a dispersal field further on from the three main ponds, towards the Kawarau river.
The dispersal field was designed around 2016 as a gravel bed to treat the final stage of sewage from the main plant and stop a previous practice of wastewater going into local rivers.
The design was controversial, experimental, the subject of cost cutting and an environmental compromise.
One of the Shotover dispersal field consultant designers for QLDC, David Potts of the LEI consultancy in Christchurch, wrote a paper for The New Zealand Land Treatment Collective (NZLTC) prior to construction. You can read the full paper here.
Here’s an extract:
“This original design required a gravel platform to limit groundwater breakout with an estimated capital cost of $19 million. To reduce cost, a system was investigated on the river-side of the protection works. To meet iwi and other stakeholder’s concerns, the new land dispersal system had to drain naturally through the underlying silts, rather than being forced through under pressure. “
“This innovative design reduced the estimated capital cost to $4.3 million. To support the operation, a number of piezometers are being installed that will be monitored to confirm groundwater mounding modelling predictions undertaken during consenting. This saving has resulted in the direct discharge of effluent to the Shotover River stopping four years earlier than planned.”
But …. it didn’t.
Something has gone seriously wrong with this innovative, discounted design and nobody apparently knows how to fix it. We understand that part of the reason is non-porous ground that is not allowing partially treated water to soak away. It also looks like there are many other elements of this experimental design that just don’t work, and probably can’t be fixed.
What was supposed to be a dry gravel bed is now a large fetid lake, overflowing semi-treated effluent into the Kawarau and Shotover rivers.
This is what the Shotover dispersal field is supposed to look like - dry gravel.
This is what it looks like this week - totally underwater. Note the newly installed 2-3 metre high banks or land barriers around the edge.
This is what appears to be a permanent discharge pipe from the dispersal field channeling water straight down to the Kawarau River.
What’s worse is that ratepayers have had to fund an emergency land barrier to contain the growing lake and Otago Regional Council scientists have captured two instances of the barrier collapsing.
For what we believe to be the past few months overflow from the dispersal field/lake has been channelled directly towards the Kawarau River from a large diameter pipe that is feeding an overflow pond.
The QLDC denies this and says all waste water leaving the plant is going via the gravity fed gravel filter system.
Here’s our photo and video evidence from Thursday, November 21st of the dispersal field overflow going into the Kawarau River and the Shotover River. Note that this waste water will not have gone through the failed gravity fed filtration system.
Video: much of the overflow comes from a large discharge pipe at the Kawarau river end of the dispersal field.
Video: From the dispersal field site the waster water is flowing through a large recreational reserve just 20 metres from the (leaking) fence and directly under the Queenstown airport flight path.
The wastewater (foreground) then flows into the Kawarau river via one, potentially two, entry points.
No work was visible around the dispersal field this week and the area looks disorganised, even abandoned - apart from a large number of new temporary orange fences (installed November 21) and warning signs. Unused water cell tiles in the foreground.
An ORC aerial image of the dispersal field starting to fail (2023) and fill with water.
An ORC image from 2023 of wastewater flowing into the Kawarau River.
An ORC image of early attempts by QLDC to stop the dispersal field disappearing under water.
ORC investigator’s image of a breach in the new earth bank erected by QLDC around the flooded dispersal field.
Video: Waste water flowing into the Shotover river from a long bush channel that leads back to the flooded dispersal field.