Cadia's water torture

Unprecedented rainfall has put Cadia Valley Operations in a predicament they’re not used to - too much water.

The impact of December’s deluge has been so significant the open cut pit will be closed for three weeks while water that has been collecting at the bottom is pumped out.

“It’s ironic to think back to where we were three years ago and in the space of just two or three months, the whole world has changed,” Newcrest Mining Limited services general manager Tony McPaul said yesterday.

Assuming no evaporation or further rainfall, the mine now has 13,700 megalitres of water stored in four dams - enough to last four years.

With further falls a possibility, crews have been working 24 hours a day to increase the capacity of three dams.

Unfortunately, the rain came too early to be captured by an expansion of the Rodds Creek Water Holding Dam.

The wall is being raised 15 metres to increase the capacity from 3700 megalitres to 14,500 megalitres.

Eight thousand megalitres, enough to fill Lake Canobolas 10 times, has also gone over the wall of Cadiangullong Dam wall since August.

Some of this could have been captured and transferred to the Rodds Creek dam had the expansion been completed.

“Hindsight is a great thing,” Mr McPaul said.

“We always planned to have the wall completed by winter, when you’d expect to get rainfall, but to 297 millimetres of rain in December alone just couldn’t be predicted.”

Just over 470 millimetres of rain was recorded during August and December.

A decision was recently made to stop pumping water out of the pit until there was more space available in the storage dams.

“We still have plenty of stockpile material so even though there are no trucks in the pit at present, we still have plenty of feed for the plant,” Mr McPaul said.

In November, Orange City Council was asked to shut down the pipe that transfers nearly nine megalitres of partially treated effluent to the mine each day.

The mine has also not needed to extract water from the Belubula River and Flyers Creek since August.

“If you’d have talked to me in June or July last year and said we’d have full dams and would have to turn the effluent off and stop harvesting against our licences, I wouldn’t have believed you,” Mr McPaul said.

Work is continuing to raise the height of two major tailings dams by six metres.

“We’re required to have the capacity to store a one in 100 year rainfall event so the Boxing Day event, which was a one in 50 year event, has chewed up some of that capacity,” Mr McPaul said.

“The extra height means if we get another major rainfall event, we can contain it.”

The rain has not affected the operation of the Ridgeway mine, Ridgeway Deeps mine or construction of the Cadia East underground mine.

bevan.shields@ruralpress.com