Tonnes of chemicals to clean up lake

Twelve tonnes of chemicals look set to be pumped in to the Utuhina and Puarenga Streams every week in a bid to clean up Lake Rotorua.

After studying different clean-up options over the last year, Environment Bay of Plenty and scientific investigators want to trial dose the two streams with alum, a double sulphate of aluminium and potassium. It is used in the coagulation process to remove particles from water.

They found this approach to be one of the cheapest, most efficient and quickest to help clean up Lake Rotorua.

Pumping alum in to the streams is expected to stop more than half of the phosphorus that flows in to Lake Rotorua from the streams.

The process will cost $500,000 to set up and there will be an additional $400,000 in running costs.

Chemical storage and dose facilities, anticipated to be no bigger than a normal sized car, will be built to hold and distribute the alum.

A base for the Puarenga Stream clean up facility has still to be chosen while it is planned to site the plant for the Utuhina Stream on an industrial site in Depot St.

The facility will include a tank holding 20,000 litres of alum, placed inside another tank, as a safety measure to stop any of the chemical seeping out.

From the tank, alum will run in to a control box, which will manage the amount that goes through to the streams.

Water quality monitoring will take place throughout the trial and investigators will also look at insects that live in the stream. They will also check algae levels and fish to see how they are adapting to the alum and determine the project's success.

Environment Bay of Plenty's environmental investigations manager John McIntosh said the alum dosage is a short- term solution and could get under way within three months.

Even though this plan will not get rid of all Lake Rotorua's problems Mr McIntosh believes it will help.

"We need a whole mix of things and this treatment of the stream is just one of the things," he said.

"This is part of a big project looking at all the things we might do."

The chemical trial is one of the action plans aimed at reducing nutrients in Rotorua's lakes and is now open to public consultation. At present there is no set time frame for the trial to be carried out but Mr McIntosh would like to see it run for two years with officials reporting back to the public after a year.

Mr McIntosh hopes to lodge resource consent for the project with Rotorua District Council and Environment Bay of Plenty within a month.

- DAILY POST (ROTORUA)