Water results raise questions on aquifer use

Water just over a month old has been found in the Brookvale Rd Bores, a GNS Science report has revealed.

In secure supplies older water is desired, as contamination in the form of living organisms cannot survive in the ground for long periods.

The report on age testing of drinking water was released today by Hastings District Council, and raises a number of questions relating to management of the aquifers in the region.

It was prepared for the council by GNS Science as part of the five-yearly assessment of the District's water supplies under the New Zealand Drinking Water Standards, and is based on water samples taken in May 2016, three months before the recent Havelock North Water Contamination event.

Hastings District Council Mayor Lawrence Yule said the results of the report released today were very interesting.

"These latest test results show a significant proportion of young water in samples drawn from the Brookvale and Wilson Road (Flaxmere) bores, and point to possible young water being drawn from the Frimley Bore," he said.

"In Brookvale for example, the youngest water is just over a month old. This has the potential to introduce bacteria into the water source."

In the past, the council had been able to supply untreated water partly because of the older age of the water.

"These results will have implications for future decision making over our water supplies," he said.

"The results may make it difficult for a number of our water sources to be classified as secure under the Drinking Water Standards."

The Council asked the GNS Science team whether young water in the samples could have been caused by a leak or fault in the bores themselves. The scientists believed this was unlikely, advising Council the tests were not sensitive enough to pick up such small quantities of water.

Significant proportions of the water flow needed to be affected to be detected through age testing which measure radioactive isotopes in the water and compares them to the levels present in rainwater.

The council was currently studying the detail of the report to assess the implications of this new information. It had also provided a copy of the information to the Hawke's Bay Regional Council to assist it in its responsibilities for managing the region's groundwater resources.

Other issues had been highlighted by the testing, including the biggest presence of young water in the aquifer system was in the "unconfined" areas of the aquifer - where more permeable gravels from the Tukituki and Ngaruroro river 'fans' fuse together with the main Heretaunga aquifer system.

Across the aquifer system, average water age seemed to be getting younger, with 'mean residence times' reducing. This might suggest levels of water abstraction might be having an influence on the aquifers although further testing would be required to confirm this.

The mixing areas between younger and older water where the aquifer is 'recharged' appeared to have moved 'downstream' closer to the core aquifer with respect to the influence of the river systems.

While the core Heretaunga Plains aquifer still provides pure, clean water, the results of the report would be of interest to a number of parties.

"Our staff are keen to discuss this work with the Regional Council in particular", Mr Yule said.

They had given permission for the report's data to feed into the ground water modelling the HBRC was doing with GNS.

It was also likely to influence future policies and decision making around levels of water abstraction - the taking of water from the aquifer for irrigation, industrial use, municipal water supply and other purposes.