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Young water the focus

Improving our understanding of the Hawke’s Bay aquifers - the way they are filled, the cap that keeps them safe, and the effects of drawing off water from them - is crucial to a raft of decisions that need to be made around drinking water supplies.

The latest science and technology have been used to investigate the underground water sources over the last six months, and some unexpected results have been discovered. New technology would continue to be employed, including using aerial mapping to reach 400m below the surface later this year.

The results of the investigations so far were presented at a public symposium, jointly hosted by Hastings District Council, Hawke’s Bay Regional Council, Hawke’s Bay District Health Board and Ngati Kahungunu, held over Thursday and Friday [June 1 and 2].

“Things appear to have changed in the aquifer over the last little while,” said Hastings mayor Lawrence Yule.

“We don’t know why yet, or the extent of the changes, but we do know there now appears to be ‘young’ water in parts of the aquifers.”

At the symposium the parties involved, Hastings District Council, Hawke’s Bay Regional Council, and the Hawke’s Bay District Health Board, recommitted to using all resources necessary to understand the full extent of the issues and to come up with solutions.

For Mr Yule, a crucial new piece of information was the greater than expected natural permeability of the gravels of Hawke’s Bay’s aquifer compared to other parts of New Zealand, and the risks to deeper water that could pose.

The symposium heard that changes to the aquifer structure could be influenced by natural movement, such as earthquakes, which could leave the aquifer unprotected in ways not easily visible on the surface.

Since the Kaikoura Earthquake, the Hutt Valley had recorded unexplained high levels of e-coli and Wellington Water was looking at urgent treatment.

The age of the water is vital. Young water potentially carried pathogens that made people ill. ESR microbiologist Dr Brent Gilpin told the symposium that those pathogens did not survive for longer than a year, hence the requirement for the treatment of drinking supplies that included water less than a year old.

The age of water is measured using, among other techniques, an element called Tritium, which is in the upper atmosphere and then decays rapidly, said GNS Science hydrologist Uwe Morgenstern. Finding Tritium in aquifer water showed recent rainfall or surface water was in the mix, along with any contaminants it could be carrying.

The biggest thing to come out of the symposium was that there was a great deal more work to do, said Mr Yule, “particularly around understanding the full extent and potential impacts of the changes in the aquifer. We also need to acknowledge that water is a taonga and life force. We have always regarded our aquifer water to be risk free but clearly it is not.

“The new information we have gained is vitally important as it will, in many ways, decide the actions we have to take on the surface to make sure people get safe drinking water through their taps.”

Hastings District Council chief executive Ross McLeod told the symposium that staff were continuing investigations into new water sources, continuing heightened monitoring of the water supplies for e-coli and protozoa, and implementing treatment options, including UV, across the network. “There is also a massive emphasis on maintenance, inspections and record keeping.”

All results and scientific findings would be shared across the parties, via a Joint Working Group made up of members from the councils and health authorities, supported by water experts.

4 October 2017

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