Favourable progress has been made with attempts to reduce the amount of algae in Wanaka's domestic water supply, following the trial of a filtration plant at the western intake, project manager Ken Gousmett reported this week.
Mr Gousmett told the Queenstown Lakes District Council infrastructure services committee on Tuesday the filtration plant had been operating since early December and the first results had come in mid-January.
Results during this peak period were "very favourable" and "[information] tells us a full-scale installation would do what is required", Mr Gousmett said.
"This comes with a high price tag but not as high as it might be. We can say with some confidence now that it will meet concerns about algae."
Wanaka residents have long complained about unsightly algae gunking up their appliances, taps and pipes and causing water-pressure problems. The algal material is not toxic and does not present public health concerns.
A report by MWH Ltd and the University of Otago presented to the Wanaka Community Board in the middle of last year outlined a range of treatment options, including drilling bankside bores to reduce algae intake ($1 million), installing microstrainers to remove some of the algae ($3 million-$4 million), or installing membrane filtration for an absolute barrier ($14 million per intake).
The council set aside $200,000 for further investigations.
It also decided to trial a Pilot Automatic Micro-Fibre filtration plant for several months and investigate the removal of algae and any other suspended solids from the lake.
Acting capital works manager Steve Hewland said in a report dated January 12 the trial meant fresh samples of algae could be analysed, giving a clearer picture of the type of algae the council was dealing with.
Another benefit of the trial was it could verify the turbidity treatment for future drinking water standards.
Mr Gousmett said the council would continue to test the water samples at various depths in the lake this month, with the hope of finding other solutions for the algae problem.
Both intakes had been cleaned in October and again last week and there had been much less algal growth since October.
"One had 100% thin coverage and the other had 80% thin coverage. Not as bad as it had been - a good outcome," Mr Gousmett said.
