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Cumulative CSG impact to trigger aquifer drawdowns

James Nason, 17/05/2012

Updated at 11:45am to include Arrow Energy response

Freshwater aquifer levels throughout large areas of the Surat Basin are predicted to drop below the 5m trigger threshold for make-good provisions due to extensive Coal Seam Gas developments, maps showing the “cumulative impacts” of combined projects show.

The predictions are contained in an Environmental Impact Statement which summarises the expected combined impacts of four major CSG projects (operated by Arrow Energy, Queensland Gas Company (QGC), Origin Energy and Santos CSG) on groundwater systems in Southern Queensland.

The report was prepared by an independent environmental consultant on behalf of Arrow Energy.

The results of another independent study on the cumulative impact of the four major CSG projects were released by the Queensland Water Commission in Toowoomba this morning.

The Arrow Energy EIS focuses on the Surat Cumulative Management Area in Southern Queensland.

However its contents have implications for landholders in all regions of Australia where large numbers of CSG wells are being developed in close proximity to aquifers relied upon for stock water and/or irrigation.

The process of extracting coal seam gas requires the de-watering of coal seams to allow gas and ‘waste water’ to flow to the surface for collection. The cumulative impact study shows that the large-scale extraction of groundwater from coal seams is likely to result in the drawdown of major freshwater aquifers in the same vicinity.

Until recently, CSG companies operating in Queensland were only required to report the predicted environmental impacts of their own projects.

However, recent changes to State Legislation in Queensland have required companies to assess and report the predicted cumulative impact of all such projects working in the same area, where two or more petroleum tenures exist. The report says cumulative impacts occur "when impacts from individual developments combine to result in an impact which is greater than the individual residual impact of each development when considered in isolation".

An Environmental Impact Statement now posted on Arrow Energy’s website provides one of the first indications of what the “cumulative impacts” of combined CSG developments on groundwater in the Surat Basin are likely to be.The report notes that impacts from each project have been assessed through the EIS process, and proposed mitigation measures will reduce the significance or risk of those impacts. This report concentrates on the remaining residual cumulative impacts of all four CSG projects. 

The below table summarises the results of the analysis, and shows that some of the groundwater systems that landholders and rural communities rely upon for freshwater could fall by 60m to 150m as a result of cumulative CSG extraction impacts. 

5m drawdown will trigger “make good” provisions

In Queensland, State Government legislation requires resource companies to “make good” any damage done to aquifers as a result of CSG extraction processes, which includes any drop in aquifer levels below a trigger level of 5m.

Provided landholders can prove that bore level losses were caused by CSG activities, the company is then required to make good. Corrective measures include drilling new bores, providing water to supplement what has been lost, such as piping or trucking in water as required, or financial compensation for water loss and associated property value loss.  

Areas within the red contour line on the above map show predicted aquifer drawdowns of 5m or more, which under Queensland legislation trigger "make good" provisions by CSG companies.

As the map (above) shows, the area likely to be affected by a drawdown of at least 5m (marked by the red contour line) takes in a large numbers of properties from east of Roma and north of Wandoan running in a 100km wide band south east to Milmerran.

The map, which shows predicted unmitigated peak drawdowns by 2024, shows that some areas are facing potential aquifer drawdowns in excess of 100m.

Another map (below) showing predicted aquifer drawdown impacts as of 2061 – 10 years after CSG production in the region is due to have ceased – shows significant lingering aquifer impacts across the same area almost 50 years from now.  

 

 

The report confirms that cumulative impact modelling reveals greater impacts than that shown by analysis of individual projects on their own.

“The modelling results show that the groundwater drawdown cumulative impact would be notably worse than the residual impact of the Surat Gas Project when considered in isolation,” the report states.

Southern Queensland landholder and Lock the Gate alliance spokesman Lee McNicholl said the cumulative impact study contained in EIS highlighted the “dire consequences” of CSG companies having already received State and Federal Government approval to pump unlimited gigalitres of groundwater from the Great Artesian Basin.

“It is now alarmingly clear the vast majority of bores in the Surat Basin will have their existing bore water levels lowered from up to 60 metres in the Springbok aquifer, up to 150m in the Walloon Coal Measures and up to 75m in the Hutton and Precipice aquifers,” Mr McNicholl said.

Arrow: Maps show worst-case scenario

Arrow Energy has provided the following response: 

"The potential drawdown predictions are a “worst case scenario” of possible total impacts from all CSG projects in the Surat — not just Arrow.

"The numbers do not take into account any mitigation or make good measures such as reinjection or substitution.

"These measures will greatly reduce the impacts currently predicted.

"Arrow Energy will continue to work closely with affected landholders to “make good” on water and bore impacts should there be a reduction in their capacity to supply water.

"Make good measures are agreed between Arrow and the owner of an affected water bore. Make good measures include:

  • deepening a bore
  • adding rising mains to lower the pump depth, thereby improving available pumping head
  • changing a pump
  • reconditioning a bore
  • drilling a new bore
  • providing an alternative water supply
  • other forms of compensation 

"Today, the Queensland Water Commission released its draft Surat Underground Water Impact Report which made it clear that there would be impacts on groundwater in a minority of bores in the Surat Cumulative Management area.

"The report finds that 97.5% of the 21,192 bores in the Surat Basin will not see any impact that could pose a risk to groundwater supply from the bore."
 

Maps and information in this article sourced from an Arrow Energy EIS which can be viewed in further detail by clicking here
 

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