New mine could crack dam floor

A NEW longwall coalmine directly beneath Woronora Reservoir has the potential to crack the dam floor and cause serious leaks from southern Sydney’s main drinking water supply, say documents produced by the Sydney Catchment Authority.

Although it considered a catastrophic leak unlikely, the authority recommended that the mining company install large plugs in its tunnels to contain water loss from the reservoir above the coalmine.

Documents obtained under freedom of information laws by the NSW Opposition show the intense behind-the-scenes battle between the US mining company, Peabody Resources, the catchment authority and the NSW Planning Department over the Metropolitan Colliery plan. 

The Planning Minister, Kristina Keneally, approved a modified version of the plan last month, as a trade-off between environmental damage and jobs. The company is still permitted to mine under the reservoir, though it will allow slightly thicker columns to support the weight of the rock and 60 billion tonnes of water above but, under pressure from the Planning Department, it was obliged to leave a buffer zone around part of the Waratah Rivulet, a previously damaged river that feeds the dam.

The documents show that the catchment authority repeatedly objected to aspects of Peabody’s proposal, referring to large sections of the company’s research as “not valid”, or based on insufficient or unreliable data.

It expects that the extraction of long panels of coal under the reservoir will crack the bedrock for 130 metres above the mine, as well as cracking the floor of the dam, but said the two sets of cracks were unlikely to connect and cause a major loss of water.

However, “depending on the nature and severity of the leak and the difficulties that may be encountered in stopping the flow, the availability of stored water in Woronora dam may be threatened for a considerable period of time,” the authority said. “Contingency planning is required and this should include provision for plugs in the mine to manage significant water inflows.”

Peabody, which will operate the mine through an Australian subsidiary company, has maintained that the mine is safe and any cracking of the dam floor will not lead to a loss of water because the earth there is already saturated.

The catchment authority and the NSW Department of Water and Energy wanted the proposal to be further amended before it went on public display, but that did not happen.

“It’s outrageous that Part 3A allows the Minister for Planning to override two key agencies in this way and to ignore the key issue, which is the security of Sydney’s water supply,” said Michael Richardson, the NSW Liberal MP who obtained the documents. “If it comes down to a choice between coal and water, I know which one most people would support.”

In her determination, Ms Keneally said that an initial proposal had to be modified to provide for a better environmental outcome, but the approved plan would still lead to $154 million in annual wages for 1950 people working in or near the mine. As a result of the modification, the company said it would leave 8.6 million tonnes of coal it had hoped to dig up in the ground. The colliery can operate for 23 years without further assessment.