Extracting coal seam gas (CSG) requires the removal of large volumes of generally saline “associated” or “co-produced” water from the coal seam.
In many areas, we do not fully understand the degree of connectivity between different aquifers, nor the extent to which groundwater sources are connected to surface waters. In some places groundwater provides the base-flow to creeks and rivers; in others, creeks recharge groundwater aquifers.
Hydraulic fracturing (fracking) causes micro-seismic events or little earthquakes intended to open up pathways for fluids or gases to flow. If these fractures intercept fissures or faults, the fracking fluids, contaminated water or gas can move into other geologic layers, contaminating the groundwater.
Bores and gas wells pierce all geologic layers between the surface and bottom of the shaft, including the aquifers people rely on for drinking water and stock or irrigation supplies. If bore casings or cement seals fail, contamination can occur. Steel casings corrode rapidly in saline water while cement seals deteriorate over time and under pressure.[iv]
The risk of any one bore hole corroding or leaking is low, but is greatly magnified by the vast number of wells proposed and the timescale over which gas and water extraction will occur.
CSG projects are planned in areas that provide drinking water to millions of people, as well as irrigation supplies in some of our most important food-producing areas. The quantity and quality of these water supplies may be at risk.
The Great Artesian Basin
The Great Artesian Basin (GAB) is a resource of national importance. It lies under 22% of Australia and is the only reliable source of water in arid and many semi-arid areas.
Springs fed by GAB waters support rare plants and animals found nowhere else.
In Queensland CSG is mostly extracted from the Walloon Coal Measures, an aquifer of GAB.
In NSW, CSG companies are targeting the Pilliga Sandstones in the southern recharge area of the GAB. A major water study is underway to better understand groundwater in this area.
The total amount of associated water to be extracted is uncertain and will depend on the eventual size of the industry. Estimates from the CSG industry, government agencies and scientists vary widely. They range from 666 – 5,400 GL/year (Industry); 126 – 281 GL/year (Qld government); and 300 GL/year (National Water Commission). Estimates from the 3 major Queensland project EIS total 61 GL/year while the Federal Government’s ‘Water Group’ estimates are 468.8 – 1,500 GL/year. [vi]
The Queensland Water Commission is building complex groundwater models to help predict and manage the impacts of extracting these huge volumes of associated water.
Pressure in adjoining aquifers could fall by up to 6,000 KPa (equivalent to 600 metres of water “head”),[viii] and cause some artesian bores to become sub-artesian, requiring expensive pumps to obtain water. Flows to some streams could be affected.
There is much about groundwater and the GAB that we do not know. It is not possible to wholly mitigate against human errors and shortcuts taken due to economic pressures. It may not be possible to ever fix pollution of aquifers, or damage to recharge areas or springs.
Queensland regulations require CSG companies to monitor groundwater and to investigate if landholders’ bores are affected. CSG companies are required to “make good” any impacts on other water users and say that the policies and regulations now in place provide protection. However, these cannot prevent damage or accidents.
Self-regulation lacks transparency and is not good enough when so much is at stake. Independent monitoring and investigation are essential to ensure that problems will not be hidden.
[i] Groundwater (Deep Aquifer Modelling) for Santos GLNG Project – Environmental Impact Statement 31/3/2009,http://www.glng.com.au/library/EIS/Appendices/P2_Groundwater%20(Deep)%20FINAL%20PUBLIC.pdf appendix P2 section 3.4.2. Accessed 18/2/11
[v] GAB Updated Resource Study http://gabcc.org.au/tools/getFile.aspx?tbl=tblContentItem&id=412 Accessed 18/2/11
[vi] http://www.abc.net.au/news/specials/coal-seam-gas-by-the-numbers/water/ Accessed 15/12/11
[viii] Groundwater (Deep Aquifer Modelling) for Santos GLNG Project – Environmental Impact Statement 31/3/2009,http://www.glng.com.au/library/EIS/Section%206/06%2006%20Groundwater%20(Section%206.6)%20FINAL%20PUBLIC.pdfsection 18.104.22.168. Accessed 18/2/11
[ix] Groundwater (Deep Aquifer Modelling) for Santos GLNG Project Environmental Impact Statementhttp://www.glng.com.au/library/EIS/Appendices/P2_Groundwater%20(Deep)%20FINAL%20PUBLIC.pdf Accessed 18/2/11