Enduring and sustainable river and ground water systems have long been a focus of community concern on the NSW North Coast.
Metgasco Limited has been exploring for coal seam gas in the region for a number of years and to date has drilled 50 wells of various types which tap into what the company describes as shallow aquifer water.
It does not specify how much carted-in domestic water and aquifer water it has used thus far, although its estimates for seven incomplete/new core, pilot and ‘conventional’ wells range from 200,000 litres through to 1 million litres per well by 2014.
Nor does it rule out produced waste water and/or treated water seeping into local aquifers.
Ultimately Metgasco intends to have an estimated 1,000 wells in commercial production in the Richmond Valley and, an as yet unspecified number in the Clarence Valley.
Dart Energy has only recently purchased an existing mining exploration tenement in the region and takes responsibility for the 15 exploration wells already sunk.
So what might this level of exploration phase and future production phase water extraction mean for North Coast rivers and aquifers?
Because Metgasco does not publicly broach this subject unless pressed on specifc issues by the media, one must look to the National Water Commission and Queensland for a sense of what may come to pass.
In June 2012 the Australian Water Commission published a CSG water management position paper which stated:
Potential risks to sustainable water management
• Extracting large volumes of low-quality water will impact on connected surface and groundwater systems, some of which may already be fully or overallocated, including the Great Artesian Basin and Murray-Darling Basin.
• Impacts on other water users and the environment may occur due to the dramatic depressurisation of the coal seam, including: - changes in pressures of adjacent aquifers with consequential changes in water availability - reductions in surface water flows in connected systems - land subsidence over large areas, affecting surface water systems, ecosystems, irrigation and grazing lands.
• The production of large volumes of treated waste water, if released to surface water systems, could alter natural flow patterns and have significant impacts on water quality, and river and wetland health. There is an associated risk that, if the water is overly treated, 'clean water' pollution of naturally turbid systems may occur.
• The practice of hydraulic fracturing, or fraccing, to increase gas output, has the potential to induce connection and cross-contamination between aquifers, with impacts on groundwater quality.
• The reinjection of treated waste water into other aquifers has the potential to change the beneficial use characteristics of those aquifers.
• Extracting large volumes of low-quality water will impact on connected surface and groundwater systems, some of which may already be fully or overallocated, including the Great Artesian Basin and Murray-Darling Basin.
• Impacts on other water users and the environment may occur due to the dramatic depressurisation of the coal seam, including: - changes in pressures of adjacent aquifers with consequential changes in water availability - reductions in surface water flows in connected systems - land subsidence over large areas, affecting surface water systems, ecosystems, irrigation and grazing lands.
• The production of large volumes of treated waste water, if released to surface water systems, could alter natural flow patterns and have significant impacts on water quality, and river and wetland health. There is an associated risk that, if the water is overly treated, 'clean water' pollution of naturally turbid systems may occur.
• The practice of hydraulic fracturing, or fraccing, to increase gas output, has the potential to induce connection and cross-contamination between aquifers, with impacts on groundwater quality.
• The reinjection of treated waste water into other aquifers has the potential to change the beneficial use characteristics of those aquifers.
Also in 2012 the Queensland Government produced the Surat Underground Water Impact Report which predicts that petroleum tenure holders will extract approximately 95,000 megalitres of water per year over the life of the industry and this extraction will impact on water levels.
There are some 21,000 water bores within the Surat CMA with bore water used for grazing, irrigation, industry and urban consumption.
Of these, there are 528 bores which are expected to experience a decline in water level of more than the trigger threshold as a result of CSG water extraction.
The trigger threshold referred to is five metres for consolidated aquifers (such as sandstone) and two metres for unconsolidated aquifers (such as sands).
Eighty-five of the 528 bores are expected to decline by more than the trigger threshold within three years.
All 528 bores tap into geological formations involved in current or proposed coal seam gas exploration and production.
Note: The Walloon Coal Measures is a geologic formation of the Great Artesian Basin (GAB). The GAB includes aquifers of economic importance and which feed springs of high ecological and cultural significance. The Condamine Alluvium overlies the GAB and is also an aquifer of major economic importance.
Of the 71 spring complexes in the area, there are five where the predicted decline in water levels in the source aquifer for the spring is more than 0.2 metres at the location of the spring.
In 2013 it was reported in a peer-reviewed paper that fugitive gas emissions from a CSG gas field near Tara in Queensland may be higher than previously thought.
This paper hypothesizes that the lowering of the water table and the alteration of subsurface strata creates enhanced soil gas exchange, which results in higher radon concentrations near CSG wells.
A previous submission from the SCU Centre for Coastal Biogeochemistry Research also highlighted a possible relationship between CSG mining activity in the Tara region and the presence of higher than expected levels of the greenhouse gas methane in the air.
