Scientific approach fixes Foxton’s water clarity issues

Published on 17 July 2017

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Foxton’s water clarity issues have been fixed for good and this will come as great news to residents who had been experiencing discoloured water.

Furthermore, Horowhenua District Council’s Water and Waste Services Manager Paul Gaydon says that the solution has been achieved by modifying and optimising the treatment process, not just adding more chemicals.

“To put it simply, we’ve enhanced the removal of the organics in the water clarifier which allowed us to optimise the pre-chlorination and then provided for an autocatalytic reaction which occurs in the sand filters and removes the manganese that discolours the water. Then a lower dose of chlorination is made to disinfect the water before it enters the reservoir. All this means no more brown water.”

Further adjustments to the process include “fine tuning” the treatment plant’s water clarifier.

Mr Gaydon said that since he started working at Council 15 months ago, one of his main priorities has been to solve Foxton’s water clarity problems.

The bore water sourced for the Foxton town supply has a high organic content and high ammonia content, making it challenging to treat and disinfect, and with “no simple fix” available.

Water clarity issues were also due to manganese, a naturally-occurring groundwater mineral, that had built-up on the water mains pipes and which had been dissolving and discolouring the water. While the water was always completely safe to drink, it had an unappealing appearance.

“We’ve done a lot of investigation work to truly understand the problem, look at all the options available, and then identify and implement the right solution to fix the problem once and for all,” Mr Gaydon said.

Last August, the pH-level of the water for the Foxton town supply was adjusted slightly to decrease its acidity and increase its alkalinity, helping stop the manganese building-up on the pipes. In addition, the water mains were being flushed every month to help remove the manganese from the reticulation.

Mr Gaydon says this work had helped improve the water clarity, but that it was not considered a long-term fix.

Sourcing water from deeper bores was also explored, however it was discovered that that water quality was actually worse.

Other alternative options considered included oxidising the water to remove the organic content by using oxygen/chlorine or potassium permanganate. This was either too slow to take effect, or worked faster but only at high concentrations of chemical. Another option identified was ozone treatment, but this came with a very expensive capital cost of several hundred-thousand dollars and ongoing operating expenditure costs.

Mr Gaydon said the solution implemented had a one-off cost of only $113,000.  A further saving of $45,000 annually would be made from the reducing the water mains flushing from monthly to bi-monthly.

He said since they adjusted the treatment process, they surveyed four of the “biggest complainants” about Foxton’s water clarity and all reported “a 100 percent improvement”.

“Foxton’s water clarity issues have been a long-time problem. But I was determined that they would become an ex-problem.”

Mr Gaydon said that the achievement was made possible with help from his Horowhenua Alliance colleagues, water treatment specialist Marcus Coley and water treatment supervisor Marcus Clifford, “for their hard work in implementing and monitoring the process changes and their suggestions along the way.”

Mr Gaydon said that work to fix the water clarity issues experienced by some Foxton Beach residents would continue. This would likely require additional water treatment plant infrastructure, costing approximately $500,000.

District Mayor Michael Feyen says that he was delighted that a water clarity solution for Foxton had finally been found.

“People in Foxton have noticed the huge improvement in their water. I know this, because they are keen to tell me,” he said.

“Council’s water services team is to be congratulated for fixing such a long-time problem experienced in Foxton, and one that some people thought could never be fixed. This is a great outcome.”

* The Horowhenua Alliance is the collaborative ‘three waters’ contract between Horowhenua District Council and Downer for the delivery of the District’s water, wastewater and stormwater services.

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Pictured: three water samples taken from the hydrant in Hetta Street, Foxton - one of the areas that was worst-affected by discoloured water. The far left water sample is from July 2015, the middle sample is from July 2016 and the far right sample is how the water is now.