Coal Seam Gas and water impact

Condomine River - water contamination has been detected at this site

One of the key concerns with Coal Seam Gas (CSG) mining is the actual or potential impact on water within and adjacent to mining regions. Extraction of methane from coal seams relies on the extraction of large quantities of water, so across the industry, it may total between approx 30 and 90 gigalitres of groundwater per year. Impacts which are broadly understood include: the likely drawdown of aquifers; depressurisation of aquifers; risk  of groundwater contamination; risk of subsidence of the surface, and salt residing in the water of coal seams being brought to the surface - estimated to be a quantity of about 1.8 million tonnes of salt per year in Queensland alone. 

Water contamination can occur in several ways - through the injection of chemicals via 'fracking'; or through chemicals that naturally exist in coal seams, being taken out and being exposed to other parts of the environment:; and potentially just from the removal of large quantities of water from aquifers or coal seams. A lateral flow of water and aquifers for example can be extremely damaging - aquifers actually differ in their water quality throughout their extent, so a lateral flow by itself can lead to changes in water quality including contamination from natural as well as introduced chemicals and substances.

Methane leaking into surrounding aquifers can occur naturally when there's a close connection between the coal seams and the surrounding aquifers but it can also occur if the wells that go from the surface down into the coal seam are not properly sealed. This has occured in a number of sites in Queensland. A similar related risk is if the fracturing of a coal seam extends out of the initial mining zone, such as into the surrounding geological strata. This type of event has occured in the United States with detrimental outcomes. The geological and engineering science of coal seam gas extraction remains full of serious gaps of knowledge - protection of water quality is arguably the highest priority.