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WATER IN MINING
The following potential uses have been identified in Queensland:
water as a supply for local farmers and communities
irrigation of agricultural crops or plantation forestry
industrial purposes (e.g. drilling, coal washing for coal mining,
cooling in power stations)
discharge of interim or occasional surpluses of treated water
into local river or weir/dam systems (if the water is treated
and conditioned to equal standards for discharge into rivers, it
can contribute favourably to environmental outcomes for river
systems already exposed to heavy irrigation demand)
reinjection, after treatment, into suitable underground aquifers.
After all feasible beneficial use options have been considered,
disposing of the water after required treatment may be permitted.
The disposal measures should, in the first instance, avoid and then
minimise and mitigate impacts on environmental values.
The CSG proponents in Queensland are considering the option
of reinjecting the treated produced water into beneficial aquifers
in the Surat Basin. Reverse osmosis (RO) is one of the preferred
treatment options to remove the salts from the produced water.
RO treatment of the produced water, in general, results in higher-
quality water than in the target groundwater aquifers.
Reinjection of treated produced water may help to augment
the groundwater resource for beneficial use and support
the groundwater-dependent ecosystems; however, the
success of reinjection depends on a number of factors, like
the hydrogeological conditions at the injection site, chemical
compatibility of water in the target aquifer, and clogging issues.
Four related CSIRO research projects funded by GISERA studied
these different aspects related to reinjection. Our study was
confined to the hydrogeological modelling of the reinjection-
induced large-scale changes in water quantity and quality in the
target aquifers (www.gisera.org.au/publications/tech_reports_
Our study applied four different models to simulate the flow and
water-quality changes occuring at different distances from the
injection wells. Two regional-scale models were used to simulate
the groundwater flow changes occuring on a regional scale over
a period of 100 years, resulting from a proposed reinjection
scheme continuing for 22 years. Two small-scale models were
used for a more precise simulation of water quality changes near
the reinjection well field. The key questions to be answered by this
How far and how long would it take for the re-injected water to
dilute background water quality? This question was posed not
because any known contaminant is expected in the re-injected
water, but as a worst-case scenario resulting from an accident
or geochemical contamination.
Are there any existing domestic or stock bores that are within
the reach of potential water quantity and quality change?
How do the inadequacies in the characterisation of the sub-
surface within the model affect the predictions?
The simulation results indicated that increase in the groundwater
pressure in the target aquifer (Precipice sandstone) would occur
over a region extending over 50 kilometres. While the maximum
groundwater pressure increase can be as high as 140 metres near
the injection wells, pressure changes in the existing stock and
domestic wells located far from the injection well field are expected
to be minimal. For example, the simulations indicated a maximum
groundwater level increase of 4.3 metres in the nearest domestic
bore, which is located 15 kilometres from the injection well field.
Predicted increase in the groundwater level indicates increased
availability of fresh water in this region. Owing to the low velocity of
flow in the Great Artesian Basin, this water may be drawn out for
beneficial purposes over many decades. Due to the presence of
impervious formations above the Precipice sandstone, groundwater
level changes in other overlying aquifers would be minimal.
The scenario of water quality change was simulated to estimate
the potential maximum distances at which any injectate present
in the water would dilute to very low concentrations (0.01). The
results indicated that the reinjected water would dilute to very low
concentrations within five kilometres from the injection wells. It is
noteworthy that the proposed reinjection schemes will use high-
quality water obtained from the RO treatment, but this scenario
was simulated to evaluate the potential maximum distances over
which impacts from water quality change may occur. Considering
that stock and domestic bores does not exist within five kilometres
from the injection wells, water quality impacts from the reinjection
scheme are considered to be minimal.
Given that the proposed injection wells are spread over a large
area, and given the uncertainty of mobilising contaminants already
present in the formation, it is still essential to continually monitor
groundwater quality for early detection and containment of any
REVERSE OSMOSIS (RO) IS
ONE OF THE PREFERRED
TREATMENT OPTIONS TO
REMOVE THE SALTS FROM
THE PRODUCED WATER.
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