The Great Artesian Basin (GAB) covers 22% of Australia and is the only reliable source of water across its overlying arid and semi-arid areas. In addition to water, significant unconventional gas resources are held within some of its aquifers or in older, deeper rocks.
Gas extraction requires drilling into GAB aquifers or right through the Basin. This creates a risk of inter-aquifer leakage via the gas well. Water quality can be impaired if water from different aquifers mixes or if it is contaminated by gas or drilling fluids. It is extremely difficult and expensive to reverse such damage. The greater the number of gas wells, the higher the risk.
Coal seam gas extraction requires the removal of some of the water in the coal seam to reduce pressure and allow the gas to flow. Environmental Impact Studies make it clear that pressure and water levels in adjoining aquifers will fall. Recovery to pre-coal seam gas extraction levels will take decades or centuries. This means negative impacts on other water users and their businesses, where they rely on those aquifers. Water Group advice to Environment Minister Burke stated there is also likely to be “a significant impact” on threatened species dependent on GAB springs.
Pressure is an extremely important and valuable resource in the GAB. Hundreds of millions of dollars have been spent by governments and landholders on the Great Artesian Basin Sustainability Initiative to save water and restore the pressure lost from uncontrolled bores. Coal seam gas extraction threatens to undermine the achievements of GABSI to date. Some landholders have decided not to rehabilitate their bores as the benefits will be cancelled by coal seam gas developments.
There are also large coal deposits in the GAB area and dozens of new mines are proposed. Open cut and underground mining cut through aquifers, interrupting the movement of groundwater and also require dewatering of coal seams. These activities have major impacts on groundwater resources and groundwater dependent ecosystems such as GAB springs.
More information about extractive industries and the GAB can be found here.