Council Fine Tunes Hydrocarbon Sensor Protecting Raetihi

Ruapehu District Council (RDC) is continuing to test and adjust the hydrocarbon sensor on Raetihi’s water intake in preparation for returning the Makotuku River as the township’s water source.

A spill from the Turoa ski field on Mt Ruapehu in October last year leaked 19,000 litres of diesel into the Makotuku River forcing RDC to switch the water source for Raetihi township to the Makara Stream.

Ever since the end of the of the civil defence response phase to the diesel spill RDC has been working to return Raetihi’s water source to the Makotuku River.

RDC Environment Manager, Anne-Marie Westcott, said that the successful installation of a hydrocarbon sensor on the raw water line feeding the Raetihi water treatment plant is a critical factor in enabling council to return the water supply to the Makotuku.

“Council is taking an extremely cautious approach in returning to the Makotuku River as Raetihi’s water source,” she said.

“The installation of a hydrocarbon sensor on a town’s water supply like in Raetihi has never been done before in New Zealand.”

“We are not willing to switch back to the Makotuku until the new systems have been thoroughly tested and we are satisfied that they are robust enough to withstand a wide range of factors.”

“In the case of the hydrocarbon sensor this includes testing it across a range of weather conditions from the current hot and dry conditions to wet and wild all of which affect things such as the river flow, run-off and water turbidity.”

“During the last heavy rain fall the hydrocarbon sensor picked-up very low readings measured in micrograms per litre.”

“As streams have natural oil in them that is released from the decay of plant material samples will need to be taken to confirm if the hydrocarbons detected is from the diesel or naturally occurring oils.”

Ms Westcott noted that this was positive and demonstrated how sensitive the sensor was at recording oils at very low concentrations.

“It may be however that the sensor has been set at too lower level than is required to detect diesel so we will be looking into that.”

“The other adjustment we have made is the installation of a float designed to keep the sensor submerged at the right level as the river flow goes up and down,” she said.

“The intake is designed to ensure that any diesel trapped in sludge is released into the water and can float to the top to be picked-up by the sensor.”

“We appreciate that the Raetihi community would like to see a return to larger Makotuku River over the current temporary smaller Makara Stream as their water supply as soon as possible but we won’t be taking any chances with the health of the community.”

Ms Westcott added that council hoped to be able to advise a target date for the switch back to the Makotuku at the next Waimarino Waiouru Community Board meeting on Thursday 13th February.

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