Diesel feared in protected river

Boom across the Makotuku Stream at Horopito. Photo/Bevan Conley

Some diesel from the September spill at Turoa may have found its way into the pristine Manganui o te Ao River - but testing by Horizons in early October found none.

The September 27 spill of 19,000 litres of diesel from a tank at the ski area saturated ground and entered the Makotuku Stream, Raetihi's usual water supply.

The Makotuku is diverted by New Zealand Energy (NZE) to generate electricity. Up to 25,920 cubic metres of water can be taken from it every day.

The spilled water then flows into the Orautoha Stream, then the Manganui o te Ao and then the Whanganui River, potentially allowing diesel through into them as well.

The Manganui o te Ao is famed for its trout fishing, blue ducks (whio) and unspoiled riverside camping at the Ruatiti Domain. It is also the subject of a Water Conservation Order, the highest level of protection that can be afforded to any water body.

Within two hours of NZE being told of the spill on October 2, the diversion of the Makotuku was stopped.

On October 3 and 4 Horizons Regional Council staff walked the Orautoha, Manganui o te Ao and Whanganui and took samples. They didn't see or smell any diesel. When the samples were analysed tiny traces of diesel were found in two taken from the Makotuku at the NZE race upstream at SH4, but none at any of the sampling spots in the Orautoha or Manganui o te Ao, or at Pipiriki on the Whanganui.

That doesn't mean none got there, because it could have passed through between September 27 and October 3, Horizons Regional Council's strategy and regulation manager Nic Peet said.

If there was some contamination, the flood on October 15-16 would have swept all traces away.

Horizons' investigation into the diesel spill could result in prosecution or a fine of up to $500,000 for Ruapehu Alpine Lifts (RAL), the owner of the diesel tank. Dr Peet said it would not be finished until at least January.

The Conservation Department is also investigating the spill. Ruapehu partnerships manager Jonathan Maxwell was DoC's controller at the incident.

He said diesel was a lightish hydrocarbon that flushed through relatively easily, and broke down in sunlight. Blue ducks were unaffected by the spill.

The tank at Turoa was double skinned and completely to standard, he said. "A hose came off its connection. It was just one of those things."

The department was now looking at how gas, petrol and diesel were stored on conservation land. At some places the fuel is stored in underground tanks that are quite old.

The Ministry of Business, Innovation and Employment's Health and Safety Group is also investigating.