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Contamination cleared from old sites

Contamination cleared from old sites
The old Prohibition Mine site at Waiuta, above, and below treatment systems for arsenic in water downstream.

Two historic New Zealand gold mine sites that were claimed to be among the most contaminated in the world have now been remediated.

In a joint statement, Environment Minister Dr Nick Smith and Conservation Minister Maggie Barry said work has been completed on the elimination of contamination from the Prohibition Mine site at Waiuta and the Alexander Mine, also in the Reefton goldfield.

Several years ago the old mine sites were designated as among the most contaminated sites in the world.

Dr Smith said the sites were cleaned up in the past 18 months in projects jointly funded by the Department of Conservation (DOC) and the Ministry for the Environment’s contaminated sites remediation fund.

The two projects cost around $3.6 million to complete. Ms Barry said the Prohibition and Alexander mine sites were acutely toxic.

“The levels of arsenic were among the highest recorded anywhere in the world at 400,000 parts per million on land, or 500 times the safe level, and in water at 300 parts per million, or 33,000 times the safe limit for drinking water,” Ms Barry said.

“The Prohibition Mine site was contaminated from the operation of a roasting plant from 1935 to 1951, when arsenic bearing ore was roasted to release gold,” she said.

“The Alexander processing plant that produced the high levels of arsenic operated between 1934 and 1936. The mine closed in 1943. “The sites also had high levels of mercury and cyanide.”

DOC took over the mining site in 1987 and had immediately fenced it off to prevent further public access.

It then prepared a remediation plan which was accepted by the Government but this was put on hold for a couple of years.

Ms Barry said that DOC engaged nine of its workers in ensuring the two mines were made safe for people to visit the mines for about an hour at a time.

Ms Barry said that at all stages of the operation, workers would be clothed in appropriate protective clothing and wear positivepressure respirators.

The work was specialised and included the demolition and disposal of the existing condensing tower which was a major area of contamination.

The DOC crew also ensured the material in the mines, which was the most highly contaminated, was removed, treated and disposed of at a specialist treatment site near Christchurch.

Contamination cleared from old sites

The crew also removed the entire surface of the site to a nearby low-lying area where it was lined and capped with mullock from the old workings of the mines.

When this had been completed the entire mine site was also be capped with mullock.

The high level of arsenic in the abandoned mines was and first recorded in 2005 by Laura Haffert, a doctoral student at the University of Otago and this resulted in worldwide publicity.

Nick Smith says he believes the contamination arose through poor oversight of operations when the mines were operating.