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Coal Seam Gas Extraction Industry
Surat Cumulative Management Area
Draft Underground Water Impact Report
Queensland Water Commission Consultation Draft – May 2012
Submission prepared by
John R Hillier
Consulting Hydrogeologist
In conjunction with and on behalf of
Central Downs Irrigators Limited and D A Hall & Co Pty Ltd
Introduction
The Draft Underground Water Impact Report for the Surat Cumulative Management Area
presents the results of the Queensland Water Commission’s investigation into the combined
effects of Coal Seam Gas extraction on groundwater in the Surat and Bowen geological
Basins. The report has been prepared for public consultation purposes and has been
presented at public meetings at various centres in the Surat Basin. This response has been
prepared in conjunction with and on behalf of the Central Downs Irrigators Limited and D A
Hall & Co Pty Ltd.
Central Downs Irrigators Limited was formed to represent irrigators in the main Condamine
River Alluvial area in the Cecil Plains area. The major source of irrigation water is derived
from the aquifers within the alluvial sediments. They are concerned about the potential
impacts of Coal Seam Gas activities on their groundwater supplies, in particular the
extraction of water from the Walloon Coal Measures from near and under the alluvium.
D A Hall & Co operate an extensive agricultural business in the Millmerran area. It
incorporates in excess of 16 properties, some of which consists of several blocks. The main
activity is poultry (egg) production, but cropping (some irrigated) and piggeries are also
important. An adequate water supply is paramount for the business to operate successfully,
and the majority of the water is sourced from groundwater, from the Condamine River
alluvium, the Walloon Coal Measures and the Hutton Sandstone.
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General Methodology
The Queensland Water Commission (QWC) followed a logical procedure in the
determination of impacts from the extraction of groundwater which is a necessary
component of Coal Seam Gas (CSG) production. This was:
o Understand the geology and hydrogeology and develop a conceptual model of the
hydrogeological systems
o Develop a computer based mathematical model to represent the conceptual model
o Calibrate the parameters used in the mathematical model in a steady state situation
using a comparison of simulated values with measured values as a guide to adjust
parameters
o Use the calibrated model to simulate impacts that groundwater extraction in
association with CSG production will have on the groundwater systems in the various
aquifers over time
The required information for this investigation was obtained from numerous sources some
of which are discussed in the following sections.
The information presented in this Underground Water Impact Report (UWIR) is somewhat
limited, especially regarding the model set up, calibration and parameters, and this does
limit a detailed technical review of the report. In some instances, further information could
possibly be made available by QWC so a more detailed review could be made and so
increase confidence in the report’s conclusions.
Detailed Comments
Conceptual Model
The conceptual model appears well developed and appears to have been based on all
available information. The most significant components in relation to the dewatering for gas
production are:
o The Walloon Coal Measures (WCM) which are a complex mix of various sediments
including sandstone, shale and mudstone and coal and is the source of the coal seam
gas
o The layers that are incorporated in the model that are directly above and below the
coal and provide some protection to impacts on overlying and underlying aquifers
o The aquifers that are closest to the WCM both above and below the productive
seams, including the Hutton Sandstone (below) and the Springbok Sandstone, the
Gubberamunda Sandstone and/or Kumbarilla Beds and the Condamine River
Alluvium, all of which are above the Walloon Coal Measures and are in contact with
the WCM as the sediments shallow to the east.
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Computer Based Mathematical Model
The conceptual model has been transposed into a groundwater flow model using
MODFLOW code, the current industry standard. MODFLOW is capable of handling the
complexities of this model which covers an area of 550 km x 660 km, has 19 layers and a cell
size of 1.5 km x 1.5 km. Superimposed on this model is a separately developed MODFLOW
model of the Condamine River Alluvium.
There is insufficient information provided to allow a detailed comment to be made on the
main model, but it is noted that it has undergone a peer review. However, based on the
information available in the UWIR, the following comments are made:
o In general, there is insufficient information to calibrate vertical permeability in
aquicludes in the model. It is assumed that “best guess” estimates have been used
and these may be a reasonable average, but may be quite incorrect in some areas.
As an example, the report states that there is a paucity of good data on the thickness
of the “transition” layer between the productive alluvium and the coal measures. In
addition, the range suggested for the vertical permeability for this layer (the only
example given) is 0.000008 to 0.15 m/d, an enormous range
o The values adopted for vertical permeability and the thicknesses of the various
aquicludes in the model are the key to the simulated impact on bores located in the
other aquifers. The values adopted by the various CSG companies for use in their
models vary considerably, as pointed out by USQ (2011) and this tends to highlight
the lack of good data available for construction of this most important aspect of the
model.
Although there is insufficient information on some aspects of this complex model to
properly calibrate it, the model of the Surat Basin part of the Great Artesian Basin is
considered to be as good as data will permit. The models limitation in the accuracy of
predictions need to be understood by those using the results. Predictions are probably
within ±2 m over much of the model area, and predictions of impacts less than this would
have a high degree of uncertainty.
The model of the Condamine alluvium that has been used (Klohn Crippen Berger, 2011) has
previously been reviewed and it is considered that it has some significant problems which
may limit its suitability to predict impacts. These include:
o There were large areas where irrigation bores were not metered and use has been
estimated. This has resulted in poor calibration in those areas
o In other areas calibration has resulted in significant differences between simulated
and measured groundwater levels
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o Many parameters (storage co-efficient and hydraulic conductivity/permeability) have
calibrated to the limit of the range permitted in the model setup, obviously
restrained by these restrictions from what the calibration program considers they
should be
o There are problems with recharge simulation, both from the Condamine River and
from rainfall, the latter being only an estimate
The limitations of this model of the alluvium casts doubt on the accuracy of predicted
impacts on this groundwater system.
Predicted CSG Dewatering Volumes
Water extraction from current and proposed CSG activity, together with the sequencing of
development, has been provided by tenure holders. Pumping rates and the relationship to
drawdown were derived from historical data.
Considering the expenditure by the tenure holders on CSG exploration, development and
then the associated production facilities and pipelines etc, it is a reasonable assumption that
they would have quite detailed development plans for future production. Some factors
(such as economic conditions, competition from other developments, Government policy,
etc) may result in the predictions differing from actual future production.
The Environmental Impact Study that was submitted by Arrow Energy Ltd in March, 2012
presents modelled impacts for their proposed future CSG developments (despite major
deficiencies in their models). It appears (from their EIS) that they modelled future impacts
by spreading probable dewatering volumes over the whole lease areas, and then modelled
the drawdown (and impacts) that would result from the pumping of that volume of water.
Drawdown at the proposed production field sites should have been the input, and pumped
volumes and the spread of drawdown in the Walloon Coal Measures and the impact on
other aquifers should have been predicted from the model.
It is hoped that more detailed information such as probable production field sites and areas
were supplied to the Commission, so modelled impacts could be based on drawdown as
well as volumes pumped and so provide a realistic basis for predictions.
The UWIR does not explain what information on future development has been provided by
the CSG companies to simulate impacts and so there is no way to check the validity of these
simulations. However, an analysis of predicted impacts in the Walloon Coal Measures and
the Condamine Alluvium indicates that the impacts from modelled pumping and drawdown
is not as would be expected if development of production fields followed the pattern that is
proposed by Arrow’s Dalby Expansion Project.
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Groundwater Impact Predictions
The results of the predictive modelling show main impacts occur in the Walloon Coal
Measures, with some long term affects in the Springbok Sandstone and the Hutton
Sandstone, the closest aquifers in the GAB, as groundwater moves from these aquifers into
the dewatered Walloon Coal Measures. The UWIR concludes that over the life of the CSG
industry in the Surat Basin, about 50% of the total water extracted will come from overlying
and underlying formations, with probable on-going movement of groundwater towards the
Walloons until an equilibrium is reached. It would assist in the understanding of the impacts
if the flow from the various aquifers could be quantified. This water has not been available
for landholders use under the Water Resource (Great Artesian Basin) Plan 2006 and has not
been factored into the Plan’s available resources.
The impacts that are of most concern are those in the eastern part of the Cumulative
Management Area, mainly the Dalby, Cecil Plains and Millmerran areas. This is because the
GAB sediments become shallower and the aerial extent of these formations is restricted due
to shallower and outcropping bedrock in the transition from the Surat Basin to the Clarence
– Moreton Basin. In addition, the Condamine River alluvium directly overlies the WCM and
could be impacted.
A. Walloon Coal Measures
An examination of the predicted impacts for the Walloon Coal Measures show where the
main drawdown centre are located. It is reasonable to assume that because of the limited
continuity of permeable beds, any production field would show as a centre of drawdown in
this formation. The centre closest to the east is around ATP764 with has a drawdown
extension to the east, caused by the existing Tipton field on PL198. There appears to be no
drawdown centre caused by extraction on PL258 or PL238 (part of the Dalby Expansion
Project) or the other leases involved in this expansion project (PL194, PL230, PL252 or
PL260). The Dalby Expansion Project is for some 300 production bores in the first stage. It is
possible that the extraction has been spread over the individual leases (which is unrealistic
with such large areas) or some has not been incorporated. Either way, further information
on proposed production areas is needed together with predicted dewatering volumes so
impacts can be related to pumping volumes.
There appears minimal impact from any production bores that would be established on
ATP683, despite all the exploratory work that has been undertaken and the petroleum
activities that have been authorised under the Environmental Authority, including 36
appraisal and/or pilot wells. As stated above, no information on extraction areas or volumes
has been given. Such information is imperative in such a large ATP as this area has extensive
groundwater use from both the Condamine alluvium, the Walloon Coal Measures and the
Hutton Sandstone. An even spread of pumping bore over the ATP gives no real idea of likely
impacts on existing users
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The prediction of impacts on the Walloon Coal Measures is considered of paramount
importance because of the large number of bores that tap this formation in the eastern area
of the Cumulative Management Area as the options of obtaining water from the aquifers
above this formation reduce on the basin margins.
B. Hutton Sandstone
The impact of dewatering of the Walloons on the Hutton Sandstone does not appear
excessive and would be dependent on the thickness and vertical permeability of the
intervening layer. This sandstone, lying below the Walloons, cannot be dewatered and head
losses can usually be overcome by lowering pumping levels.
It is noted, though, that the largest drawdown impacts in the Hutton Sandstone do not
correspond to the largest drawdown in the Walloon Coal Measures.
C. Springbok Sandstone and Kumbarilla Formation
The impacts on these formations are again dependent on the permeability of any sediment
between the Walloon and the sandstone above. The modelling indicates impacts of about
10 m in the Dalby area with impacts of between 5 and 10 m between Dalby and Cecil Plains.
In most of this area, use from these formations is not large as water can be obtained from
the overlying Condamine alluvium.
D. Condamine Alluvium
The impacts predicted by the modelling on the Condamine Alluvium are minimal. Largest
impacts of about 1.2 m are near Chinchilla, outside the main irrigation area. Predicted
impacts around Dalby are about 0.5 m with no impact east of Cecil Plains where Arrow
Energy have an issued Environmental Authority over ATP683. It is stated that “the average
estimated net loss from the Condamine Alluvium ... is expected to be about 1,100 ML/year
over the next 100 years”. This figure appear to be very conservative – my calculated loss is
1050 ML/year (and could be up to 1970 ML/year) from the alluvium on ATP683 alone. It
would be more than twice this over the whole alluvium. Such drainage volumes will cause
drawdown but even if the 2 m “make good” limit is exceeded, it will not be able to be
separated from the drawdown caused by irrigation. Because of the volume likely to be lost,
irrigators could have reduced entitlements.
It does appear that the impact of any CSG development which lies under the Condamine
Alluvium has not been fully factored into the model or the strata that lies between the coal
and the alluvium has such a low permeability that very little movement of water would
occur.
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Other Impacts
Concern has been expressed by landholders that the Coal Seam Gas activity could lead to
other impact:
o Enhanced migration of gas could occur, from the coal seams where it is currently
held by groundwater pressure, into other aquifers and into water supplies. Problems
could occur with some pumping equipment, distribution pipelines, desalination
equipment and stock and domestic supplies. Although some aquifers are known to
contain gas, this can be handled from the start with gas release chambers and valves
etc, but considerable expense could be incurred if bores commence to produce gas
as a result of migration from another formation.
o As groundwater levels are reduced in the Walloon Coal Measures, water will move
to the dewatered area from other aquifers within the Walloon Coal Measures as well
as from adjacent aquifers. Often the sandstones within the Walloons contain very
poor quality water – worse than that contained in the usually more permeable coal
seams. This could lead to a reduction in water quality for users of groundwater from
the Walloons, with additional treatment costs involved. It is assumed that “make
good” provisions would apply if it could be proven that CSG activity was the cause,
but “make good” could be costly and difficult to implement if quality changes are
slow as would be expected.
Water Monitoring Strategy
The water monitoring strategy as proposed appears satisfactory, though it is disappointing
that comprehensive monitoring was not commenced earlier to provide a clearer picture of
the pre CSG conditions.
The actual results of the monitoring need to be available through a public accessible data
base so interested parties can view the data. Such a data base would be best hosted by the
Queensland Water Commission
Conclusions
Modelling
The perceived deficiencies in the modelling are:
o A lack of good data that defines the vertical permeability of the aquicludes, in
particular the transition zone between the Walloon Coal Measures and the
Condamine alluvium
o The model of the Condamine alluvium, which has quite identifiable shortcomings
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o The data supplied by Coal Seam Gas Companies on the their proposed extraction of
groundwater and the sites of future production fields. This is the most important
component in predicting impacts of the ongoing Coal Seam Gas industry
The prediction of impacts of extraction from the Walloons on landholders bores tapping the
Walloons and all surrounding aquifers is the whole purpose of this report and unless there is
confidence in the data supplied on future development, the benefit obtained from the
development of the model may be limited.
Other Impacts
Migration of gas from the coal seams into productive aquifers could occur, though it is
acknowledged that this can happen under natural conditions. The possibility of this being
enhanced by CSG extraction should be quantified.
Similarly, the possible migration of salts between aquifer could also cause problems for
landholders.
Monitoring
The results of the monitoring need to be made available to interested parties in a timely
manner. This could be achieved by the establishment of a public accessible data based,
probably controlled by the QWC.
John R Hillier
22 June 2012
References
Klohn Crippen Berger, 2011. Central Condamine Alluvium, Stage IV – Numerical Modelling
Final Draft Report. Report prepared for Queensland Department of Environment and
Resource Management.
University of Southern Queensland (USQ), 2011. Preliminary Assessment of Cumulative
Drawdown Impacts in the Surat Basin Associated with the Coal Seam Gas Industry. Report
by USQ, March, 2011.