CSG mining feared

TWO University of Sydney professors have urged the NSW Government to exercise caution when considering applications for coal seam gas (CSG) exploration.

In a submission to NSW Parliamentary inquiry into CSG exploration, associate professor Willem Vervoort and Dr Floris van Ogtrop, from the university's hydrology research laboratory, said the Government should be very cautious with CSG exploration licences until high-value (in dollar terms) and long-term (50 years minimum) bonds or guarantees were obtained from mining companies.

They also sought solutions for the safe and sustainable disposal of CSG waste products and more understanding about the connectivity of different underground aqui- fers and the medium and long-term effects of depressurising coal-seam aquifers.

They said there was difficulty assessing some of the risks of CSG extraction because of some of the characteristics of groundwater.

"Groundwater is extremely slow moving, can be very deep underground and is often under pressure," the professors wrote.

"There is increasing understanding that impacts on groundwater take a long time to become evident."

They said CSG mining relied on reducing water pressure in gas-holding rock layers.

"The problem with this process is that the pore space in almost every underground rock layer is connected with other layers," they said.

"Dewatering of one part of the overall underlying geological system cannot be seen separate from the effects on the other parts.

"Dewatering of rock layers causes irreversible changes to the rock system as the system is under immense pressures.

"The characteristics of groundwater combined with the extraction process of CSG means there is a substantial risk of irreversibly damaging the underlying aquifer system or causing mixing of saline and fresh groundwater.

"However, it might take tens of years to hundreds of years for this to become visible or noticeable.

"Long-term monitoring and guarantees need to be in place to protect the public groundwater resources."

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