Further work on sewage treatment

Lake Hawea's sewage treatment system will undergo work this month to improve its wastewater results, which continue to exceed resource consent conditions.

Wastewater readings taken from the oxidation ponds' discharge trench are showing higher than permitted nitrogen and ammonia-nitrogen levels.

At yesterday's Wanaka Community Board meeting, 3 Waters and solid waste senior engineer Rob Darby explained the scheduled work which aimed to mitigate the amount of nitrogen being discharged.

Semi-submerged monitoring balls would be used to track the flow within the ponds and determine whether the sewage was moving too quickly from the inlet to the outlet.

The work would also involve the installation of ''baffle curtains'', which would create ''a bit of a maze, so the sewage can not take a shortcut to the exit point'', Mr Darby told the Otago Daily Times.

''It has to follow a path through the ponds to get maximum treatment time in the ponds.''

At the board meeting, deputy mayor Lyal Cocks asked if the desludging carried out in February last year had helped wastewater results, as had been expected.

Council infrastructure engineer Nicola Greaves said pond performance had not improved as much as was hoped and there were still issues with nitrogen levels.

Mr Darby said the work was expected to cost nearly $25,000.

lucy.ibbotson@odt.co.nz