Environmental Engineering Reference
In-Depth Information
3.2.1.1 Groundwater Depletion
'Produced water' that is not recycled or re-injected depletes aquifers; in the
fullness of time, the vacuums created will be filled with water seeping in
from elsewhere, lowering water tables in general. The quantities of with-
drawals for CSG extraction will be truly vast. Because so much of the CSG
action will be concentrated in the Great Artesian basin (GAB), basin-level
analysis is essential. According to the National Water Commission (NWC),
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planned CSG development will, at full operation, withdraw more than 300
gigalitres of groundwater annually from the GAB, i.e. more than 60% of total
allowable withdrawals. This 60% for CSG implies some combination of
displacing existing uses and pushing total withdrawals well above sustain-
able levels. The NWC estimate is thought to be relatively conservative: CSG
industry sources offer a somewhat lower projection, but the federal gov-
ernment's 'Water Group' suggests, based on its case studies of the Surat and
Bowen sub-basins, that GAB-wide withdrawals may exceed the NWC estimate
considerably.
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The theory of complex systems suggests that it is near-impossible to pre-
dict the cumulative impacts on groundwater over several centuries, because
the GAB hydrological system is much too complex and the cumulative shock
to the system from CSG development will be much too large to be charac-
terised with standard groundwater models and modeling methods.
31,36
The
Queensland Water Commission (QWC) has made a serious effort to build a
model to analyse the cumulative impact on groundwater of planned CSG
development in the Surat region.
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They model movement of water among
twenty geological layers from the surface down well below the coal seam, in
response to planned dewatering. The models are best described as compli-
cated rather than complex, because they are essentially reductive and
therefore unable to capture the emergent possibilities in complex systems.
Nevertheless, the effort is to be applauded because it is really important to
make progress in projecting cumulative impacts and we should not be too
critical of reductive modeling approaches, given the relatively tentative
progress that has been made in complex systems modeling. QWC predicts
serious depletion of water tables in some parts of the Surat, and the specific
bores and wells most likely to be impacted have been identified. Intuition
suggests that their projections may understate the eventual impacts for two
reasons: unaccounted complexity of the system is likely to magnify impacts,
and impacts are likely to persist and perhaps accelerate beyond the time
horizon of their models.
At the site and project levels, farmers and settlements using artesian water
worry that water pressures and levels will fall, wells and bores will need to be
drilled deeper, and some may dry-up completely (and the QWC models
validate that concern in some cases). The Queensland government has in-
sisted on 'make good' provisions, requiring operators to provide water to
land users facing reduced and more expensive groundwater supplies as a
result of CSG activity.
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'Making good' is intended to compensate in-kind for
any harm that may arise from extracting water to release the gas, but three
