Groundwater and the Great Artesian Basin

  • Coal seam gas (CSG) in Queensland is extracted from 200 – 1,000 metres deep in the Great Artesian Basin (GAB).
  • The 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.
  • GAB springs... support rare plants and animals found nowhere else.
  • Extracting CSG requires the removal of large volumes of generally saline “associated water.”
  • Pressure in adjoining aquifers will fall[i] and flows to some streams could be affected.
  • There is likely to be “a significant impact” on threatened species dependent on GAB springs.[ii]
  • Hydraulic fracturing (fracking) could result in contamination of groundwater by gas, saline water or fracking fluids.
  • There is much about groundwater and the GAB that we do not know. It may not be possible to ever fix pollution of aquifers, or damage to recharge areas or springs.

There are no substitutes for water.

In Queensland, CSG is extracted mostly from the aquifer known as the Walloon Coal Measures. The extraction of associated water could lower water levels in adjoining aquifers[iii] or in shallower, alluvial systems.[iv] Levels in the Walloon Coal Measures will not begin to recover until 70 years after CSG extraction has ceased.[v] The Springbok and Precipice sandstones will not have recovered after 200 years. In the case of the Hutton Sandstones, recovery could take a thousand years.[vi]

Pressure in adjoining aquifers could fall by up to 6,000 KPa (equivalent to 600 metres of water “head”),[vii] and cause some artesian bores to become sub-artesian, requiring expensive pumps to obtain water.

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.[viii]

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. Fracking has been known to split bore casings and even completely shear them[ix].

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. It is not possible to wholly mitigate against human errors and shortcuts taken due to economic pressures.

We do not know 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. Nor do we understand the role or importance of hundreds of species of stygofauna – tiny organisms that live deep underground. A great deal of research is under way to better understand these complex relationships[x].

Queensland regulations require CSG companies to monitor groundwater and to investigate if landholders’ bores are affected. Self-regulation lacks transparency and is not appropriate when so much is at stake. Independent monitoring and investigation are essential to provide confidence that problems will not be hidden. 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.

Farmers fear that, with little or no data on the status and level of groundwater before CSG extraction, it will be impossible to prove that gas extraction caused the decline in groundwater levels, methane pollution of their water, or other damage to their bores or water supplies. The companies responsible for the damage may no longer exist.

References 

i  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%28Section%206.6%29%20FINAL%20PUBLIC.pdf section 6.6.2.5

 ii  Water Group Advice (to Minister Burke) on EPBC Act Referrals, QGC referral - 2008/4399; Santos-Petronas referral - 2008/4059 and AP LNG referral - 2009/4974

 iii  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%28Deep%29%20FINAL%20PUBLIC.pdf  appendix P2 section 3.4.2

 iv Hillier, J.R.  Groundwater connections between the Walloon Coal Measures and the Alluvium of the Condamine River, August 2010

 v Water Group Advice (to Minister Burke) on EPBC Act Referrals, QGC referral - 2008/4399;

Santos-Petronas referral - 2008/4059 and AP LNG referral - 2009/4974

 vi  Groundwater (Deep Aquifer Modelling) for Santos GLNG Project Environmental Impact Statement http://www.glng.com.au/library/EIS/Appendices/P2_Groundwater%20%28Deep%29%20FINAL%20PUBLIC.pdf

 vii 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%28Section%206.6%29%20FINAL%20PUBLIC.pdf section 6.6.2.5

 viii Mavroudis, D. Downhole Environmental Risks Associated with Drilling and Well Completion Practices in the Cooper/Eromanga Basins, PIRSA 2001

ix Tory Shenstone, “Learning to Lead” seminar, Brisbane EKKA, 2009 

x National Water Commission, Groundwater Projects

http://www.nwc.gov.au/www/html/157-national-groundwater-action-plan-projects.asp.

 

[Thanks to Sarah Moles for the content of this factsheet.]

 

 

 

 

 

 

 

For more information on the campaign against coal and coal seam gas see www.sixdegrees.org.au.