A preliminary hydrochemistry model and isotope assessment · 9.0 A preliminary hydrochemistry model...
Transcript of A preliminary hydrochemistry model and isotope assessment · 9.0 A preliminary hydrochemistry model...
145
9.0 A preliminary hydrochemistry model and isotope assessment
146
9.0 A preliminary hydrochemistry model and isotope assessment
# Department Condition Description Completion date Status
Pre-Dec 2012 Post-Dec 2012
10 49bCompletion of preliminary hydrochemistry conceptual model. Justification of water quality trend indicators
April 2013
11 49b Completion of Isotope studies April 2013/April 2014
12 49b, 52d iiSubmission of integrated hydrochemistry report. Commitment to provide baseline definition of groundwater quality in the Northern Gas Fields
October 2014
62 49b Review and update of water quality trend indicatorsApril 2016 and thereafter at three-yearly intervals
Commitments completed Evergreen Commitments
Commitments work in progress Firm deliverables for that month
9.1 INTRODUCTION
Investigations into the Surat Basin’s hydraulics have included improving the understanding of the regional
hydrochemistry. Detailing of the regional hydrochemistry and delineation of localised flow paths and mixing
zones will allow development of a hydrochemical model of groundwater character distribution. This model can
assist in assessments of potential impacts due to CSG activities. An initial hydrochemical model necessarily
requires development of a number of hypotheses. As more data is generated by the growing QGC monitoring
network, these hypotheses fare further scrutiny. Initial isotope pattern characterisation will also be tested
against additional data, particularly isotope relationships in springs flows as part of the overall springs
assessment approach. An understanding of the regional hydrochemistry within the area of QGC’s tenements in
the Surat Basin has been developed as part of investigations into the hydraulics of the basin. Once the regional
hydrochemistry is detailed, localised flow paths and mixing zones can be delineated and a hydrochemical model
of groundwater character distribution can be developed for use in assisting assessments of potential future
impact from CSG operations.
This chapter addresses the requirements of Commitments 10 and 11 also QGC’s Stage 2 WMMP (QGC, 2012a). A
full description of the model is contained in Appendix K. The aim of the assessment is to present hydrochemical
information that can be used to support a number of activities required under the water management
commitments.
These include:
• Development of the approach to groundwater quality trend analysis;
• Development of an exceedance response plan for aquifer contamination;
• The development of a hydrochemical model to re-establish aquifer water quality during aquifer
repressurisation;
• Support for the quantification of hydraulic connectivity between different formations (aquifers and
aquitards) ; and
• Support for the understanding and interpretation of groundwater quality and water quality change in
relation to MNES springs.
147
An initial review and interpretation of currently available isotopic data has also been included. The
characterisation provides the foundation for a conceptual model of the reaction processes that occur along
the regional flow paths. The model will be developed further with the continual collection and analysis of
groundwater quality and drill core data. The continuing evaluation of hydrochemistry will be used to support
conclusions on the groundwater hydraulics of the Surat Basin.
9.2 METHODOLOGY
A detailed assessment of groundwater chemistry data available to QGC was carried out. This included data from:
• QGC’s groundwater monitoring program;
• QGC gas well chemistry;
• Bore baseline survey data; and
• DNRM data that was subject to a rigorous QA/QC process to improve confidence in the monitored formation.
The following key activities were carried out:
• The major ion hydrochemical facies for each groundwater sample was identified. A hydrochemical facies is
a characterisation of a water sample in terms of the relative concentration of major ions. It is the chemical
culmination of the history of chemical reaction processes having occurred along the flow path before the
sampled location;
• The facies were mapped by creating three groups of stratigraphic units:
• The Upper units (Cretaceous, Gubberamunda Sandstone and Westbourne Formation);
• The Middle units (Springbok Sandstone and Walloon Subgroup); and
• The Lower units (Hutton Sandstone, Evergreen Formation, Precipice Sandstone and Base Jurassic);
• The categories logically group the aquifers and aquitards below the Walloon Subgroup, combine the Walloon
Subgroup with the Springbok Sandstone, which is considered to be the most sensitive formation to impacts
from CSG production in the Walloon Subgroup, and combine the formations above this;
• XY plots of the molar equivalent concentrations of the major ions were constructed for each vertical group of
units (Upper units, Middle units, Lower units) and for each lateral area (North, South, West);
• Concentrations of major ions were plotted against total bore depth or bottom of screened interval, where
available, to assess the vertical trends of the major ions identified by the hydrochemical facies signatures;
• Isotopic signatures were evaluated spatially and with depth. The potential relationships between different
isotopes relative to the processes that control fractionation were assessed. The results were used in
conjunction with the hydrochemical interpretations to develop hypotheses in relation to the solution mixing
and water-rock and gas-rock reactions that could be contributing to the observed isotopic trends; and
• Preliminary geochemical modelling was carried out to establish the mechanisms by which groundwater
composition is evolving.
148
Figure 9-1 – Regional hydrochemical study sample type, formation and location
_̂
_̂
_̂
_̂_̂_̂
_̂
_̂
_̂
_̂
_̂
_̂
_̂_̂
_̂
_̂_̂_̂
_̂
_̂̂_
_̂
_̂
_̂
#
#
#
#
#
#
#
# ##
#
#
#
#
#
#
#
#
#
#
#
##
###
#
##
#
###
#
#
#
##
##
#
#
#####
#
###
#
#
#
##
#
##
###
###
#
##
#
##
##
###
##
#
#*
#*
#*
#*
#*
#*#*
#*#*#*#*#*
#*
#*
#*
#*
#*#*#*
#*
#*#*#*
#*
#*#*#*
#*#*
!A
!A
!A
!A!A
!A
!A
!A
!A
!A
!A!A
!
!
!
!
!
!!!
!
!!!
!!!
!!!
!
!!!!
!!
!
!
!
!
! !
! !
!!!
!!!
!
!
!!
!
!
!
!!
!!
!
!
!
!
! ! !
!
!!
!!
!
!
!
!
!
!
!!
!! !!
!
!
!!!
!!
! !!
!!
!
!!
!
!!
!!!!
!
!
!!!!!!!
!
!
! !
!
!!!
!! !!
!!!!!!
!
!!!
!!
!!!
!
!!
!
!!!!
!
!
!!
!!
!
!
!
!! !!
!
!
!
!
! ! !
!
!
!
!
!
! !
!
!
!
!
!
!
!
!
!!
!
!!
!
!
!!
!
!!
!
!
!
!
!!!
!
!
!
!
!!
!!!!
!!
!!
! !
!
! !
!
!
!
!
!!
!
!!
!!!! !!
!
!
!
!
!!
!
! !
!
!
!
! !
!
!
!!! !
!
!
!
!
!
!!
!
!
!
!
! !
!
!
!
!
!
!
! ! !!
!
!
!
!
!
!
!
!
!
!!
!
!
!
!
!
!
!
!
!!
!
!!
!!! !!
!
!!!
!
!
!!
!
!
!
! ! !!!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!
!!
!
!!
!
!
! !
!!!
!
!
!
!
!
!
!
!
!
!!
!!
!
!
!
!
!
!
!
!!
!!!
!
!
!
!
!
!
!
! !
!
!
!
!
!.
!.
!.
!.
!.
!.
!.
!.
!.
!.
!.!.
!.
!.
!.
!.!.!.!.
!.
!. !.
!.
!.!.
!.
!.
!.
!.
!.!.
!.
!.
!.!.
!.
!.
!.
!.
!.!.
!.
*
*
BowenBasin
WANDOAN
THEODORE
G
FE
D
C
B
A
G'F'
E'
D'
C'
B'
A'
Surat Basin
Clarence-MortonBasin
New England Fold Belt
Bowen Basin
New England Fold Belt
Lila
JenWill
AlexCam
Kate
Sean
Ross Carla
Arvin
Harry
Owen
David
Codie
Acrux
Grace
Teviot
Justin
Myrtle
Peebs
Kenya
Clunie
Poppy
Argyle
Cassio
Lauren
Jordan
Polaris
Barney
Lawton
Marcus
Connor
Celeste
Andrew
RubyJo Isabella
Mamdal
Jammat
McNulty
Cougals
Michelle
Bellevue
Kathleen
Margaret
Aberdeen
Pinelands
Maire Rae
Glendower
Ridgewood
Kenya East
Broadwater
Berwyndale
Avon Downs
Matilda-John
Woleebee Creek
Paradise Downs
Berwyndale South
ROMA
DALBY
MITCHELL
CHINCHILLA
GOONDIWINDI
!. Town/City
Cross Section Lines
! DNRM Sample - Gubberamunda SST
! DNRM Sample - Westbourne FM
! DNRM Sample - Springbok SST
! DNRM Sample - Walloon Subgroup
! DNRM Sample - Hutton SST
! DNRM Sample - Precipice SST
!A Monitoring Bore - Springbok SST
!A Monitoring Bore - Gubberamunda SST
#* Baseline Sample - Cretaceous
# Baseline Sample - Gubberamunda SST
# Baseline Sample - Westbourne FM
# Baseline Sample - Springbok SST
# Baseline Sample - Walloon Subgroup
# Baseline Sample - Hutton SST
# Baseline Sample - Evergreen FM
# Baseline Sample - Precipice SST
#* Baseline Sample - Base Jurassic
_̂ CSG Well Sample - Walloon Subgroup
QGC Field
Basins
Regional Hydrochemical Study Sample Type, Formation and Location
Map Projection: GDA 94
DATA SOURCE: Towns, Basins - GARegistered Waterbores - DNRM "Based on or contains data provided by the State of Queensland (Department of Natural Resources and Mines) 2013. In consideration of the State
permitting use of this data you acknowledge and agree that the State gives no warranty in relation to the data (including accuracy, reliability,completeness, currency or suitability) and accepts no liability (including without limitation, liability in negligence) for any loss, damage or costs(including consequential damage) relating to any use of the data. Data must not be used for direct marketing or be used in breach of the privacy laws."
Note: Every effort has been made to ensure this information is spatially accurate.The location of this information should not be relied on as the exact field location.
SCALE: (A3)
DATE:
CREATED BY:
MAP NO:
REV NO:
M_30071_0119/07/2013
TM A
0 10 20 30 40 50 60 70 80 905Kilometers
±1:1,350,000
Regional hydrochemical study sample type, formation and location
0
Kilometres
50 100
149
9.3 DATA SOURCES
QGC is collecting a groundwater hydrochemical data set from CSG wells, purpose-built vertically nested
groundwater monitoring bores and a bore baseline program that assesses privately owned groundwater bores.
This data, in addition to historical groundwater data from the Department of Natural Resources and Mines
(DNRM) (previously DEHP, Department of Environment and Resource Management), provides a spatially and
vertically extensive dataset to develop a more detailed understanding of the groundwater hydrochemistry in the
QCLNG project area.
The four key data sources comprise:
• QGC’s groundwater monitoring bore network – the first phase of twelve monitoring bores completed in the
Gubberamunda Sandstone and Springbok Sandstone were sampled between October 2011 and January 2012;
• QGC’s Surat Basin bore baseline program – 106 samples collected between May 2011 and September 2012;
• QGC’s coal seam gas wells (CSG) – a selection of 24 samples for regional evaluation and the complete dataset
for evaluation of data spread, collected between March 2010 and November 2012; and
• DNRM groundwater bore database – a subset selected by applying the quality assurance and quality control
(QA/QC) methods developed by the Geological Survey of Queensland (GSQ), (sample dates not recorded).
Drilling and installation of monitoring bores is ongoing as described in Chapter 3. Future sampling from these
bores will provide groundwater quality samples from the Hutton Sandstone and Precipice Sandstone, in addition
to the Gubberamunda Sandstone and Springbok Sandstone.
A major revision of the hydrochemistry of the Walloon Subgroup will be possible once the gas wells begin
pumping.
Figure 9-2 – Durov plots for CSG well samples for Berwyndale South and Lauren fields
Groundwater Analyses - Lauren Field
Mg++
Na+ + K
+80%
50%
20%
Ca ++80%
50%
20%
SO4--
Cl –80%
50%
20%
HCO 3– +
CO 3--
80%
50%
20%
500
1000
1500
2000
2500
3000
6.0
7.0
8.0
9.0
10.0
TDS (mg/l)
pH
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
M
M M M
M
I
I I I
I
I
I I I
I
J
J J J
J
J
J J J
J
J
J J J
J
O
O O O
O
O
O O O
O
O
O O O
O
O
O O O
O
O
O O O
O
O
O O O
O
O
O O O
O
20%
20%
20%
40%
40%
40%
60%
60%
60%
80%
80%
80%
Mg
++
Ca++
20%
20%
20%
40%
40%
40%
60%
60%
60%
80%
80%
80%
SO4 --
Cl–
SO4-- +
Cl–
Ca ++ + Mg ++
HCO 3– +
CO 3--
Na + + K +
80%
80%
60%
60%
40%
40%
20%
20%
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
M M
M
I I
I
I I
I
JJ
J
J
J
J
JJ
J
OO
O
O O
O
O
O
O
O
O
O
O O
O
O O
O
150
9.4 DATA ANALYSIS TECHNIQUES
Seven cross-section lines were created across the study area to capture potential hydrochemical trends along
known regional groundwater flow paths and along and across geological formation dips. The lines were placed
across areas of highest concentration of data points and all data sources located within a 20 km offset for each
cross-section were included. The cross-section lines (A-A’ through G-G’) and the data points for each data set,
identified by formation, are displayed in Figure 9-1.
The hydrochemical data were imported into the Geochemist’s Workbench (GWB) software to identify the major
ion hydrochemical facies for each sample and to plot the data and assess trends. The hydrochemical facies of
groundwater and the facies distribution provide the basis for developing hypotheses to evaluate the potential
for chemical character produced from the interactions with the minerals in the aquifer and aquitard media
and the mixing of groundwater from various sources driven by the local and regional flow paths. Hence, the
hydrochemical facies is the chemical culmination of all the reaction processes having occurred upgradient of the
sampled location.
Piper and Durov diagrams (see Figure 9-2) which display the contributing amounts of major ions in each sample,
were produced in GWB to assess similarities and differences of the various data sets. (The Durov plot is similar
to the Piper plot in that it displays the normalised relative major ion percentages for each sample but also plots
the additional parameters, total dissolved solids (TDS) (a measure of salinity) and pH). The hydrochemical facies
were mapped using a geographic information system (GIS) to identify spatial facies groups and to assess the
data relationships for each sample point with regard to regional flow patterns, surface geology and contributing
aquifers.
To assess the vertical trends of the major ions identified by the hydrochemical facies signatures, the
concentrations were plotted against total bore depth or bottom of screened interval, where available. The data
along cross-section A–A’ (see Figure 9-3) was also plotted vertically along the cross-section line developed in
Petrel (a 3D geological modelling package), to visualise the vertical continuity and transitions the grouped facies
exhibit and the relationship to regional flow vectors (Figure 9-4). The lateral and vertical data mapping is a
significant first step in characterising the major ion hydrochemistry of the study area.
XY plots of the major ions, presented in laterally (North, South, West) and vertically (Upper Units, Middle Units,
Lower Units) proximal groupings (defined in text below), were created in GWB to evaluate the molar equivalent
concentrations of the ions spatially. This assists in identifying the possible reaction processes occurring along the
flow paths. Isotopic trends were evaluated spatially and in relation to depth. Interrelationships were considered
for possible groundwater mixing and water-rock reaction processes. The interpretation of these relationships
was used to formulate hypotheses to be tested with respect to the possible processes controlling isotopic
fractionation in the subsurface that may contribute to an understanding of hydrochemical facies distributions.
Basic geochemical equilibrium-speciation-saturation (ESS) and reaction path modelling (RP) was used to
investigate the possible reactions contributing to the distribution of hydrochemical facies. The model constructs
are based on the assumption of thermodynamic equilibrium and a generalised aquifer and aquitard media
composition to represent regional trends. This approach is considered appropriate given the generally long
groundwater residence times and the relationship between the aqueous geochemical composition of the
groundwater and the aquifer media mineralogy. The system is potentially at or close to thermodynamic
equilibrium, however, redox equilibrium is unlikely. The latter does not preclude meaningful modelling results,
because redox sensitive species do not contribute to the major ion hydrochemical facies signatures.
151
Figure 9-4 – Vertical cross-section of hydrochemical facies along A-A’
Stratigraphic Units:
Cretaceous Gubberamunda Sandstone Westbourne Formation
Springbok Sandstone Walloon Subgroup Hutton Sandstone
Evergreen Formation Precipice Sandstone Base Jurassic
No dataMixed
Na–[CI–HCO3] Na–HCO3 Na–CI
m (000)
800
600
400
200
0
-200
-400
-600
-800
-1,000
-1,200
-1,400
No data
Woleebee Creek Bellevue Poppy Ruby-Jo
m A
HD
A’ A
Na–HCO3
Na–HCO3
Na–Cl
Na–Cl
Na–Cl
Na–Cl
Na–[Cl–HCO3]
Na–[Cl–HCO3]
20 40 60 80 100 120 140 160 180 200 220 240 260 280 3000
Hydrochemical facies:
Bore water type:
Vertical Exaggeration = 75x
Regional hydrochemical study hydrochemical
facies of upper, middle and lower unites combined
Kilometres
Scale 1:1,350,000 (A3)
X
X
X
X
X
XX
X
X
X
X
X
X
X
X
X
X
X
X XX
XX
X
XX
X
XX
X
X
X
X
X
X
X XX
X
X
X
X
G
F
E
D
C
B
A
G'
F'
E'
D'
C'
B'
A'
ROMA
TARA
BELL
SURAT
OAKEY
DALBY
MILES
TAROOM
INJUNE
YULEBADULACCA
WANDOAN
GAYNDAH
PROSTON
MITCHELL
EIDSVOLD
JANDOWAE
THEODORE
ST GEORGE
INGLEWOOD
MUNDUBBERA
PITTSWORTH
MILLMERRAN
CHINCHILLA
WALLUMBILLA
CECIL PLAINS
Lila
JenWill
AlexCam
Kate
Sean
Ross Carla
Arvin
Harry
Owen
David
Codie
Acrux
Grace
Teviot
Justin
Myrtle
Peebs
Kenya
Clunie
Poppy
Argyle
Cassio
Lauren
Jordan
Polaris
Barney
Lawton
Marcus
Connor
Celeste
Andrew
RubyJo Isabella
Mamdal
Jammat
McNulty
Cougals
Michelle
Bellevue
Kathleen
Margaret
Aberdeen
Pinelands
Maire Rae
Glendower
Ridgewood
Kenya East
Broadwater
Berwyndale
Avon Downs
Matilda-John
Woleebee Creek
Paradise Downs
Berwyndale South
Regional Hydrochemical StudyHydrochemical Facies of Upper, Middle and Lower
Units Combined
±0 25 50 75 100
Kilometers
DATA SOURCE: Towns - GAWaterbores - DNRM
Map Projection: GDA 94 SCALE: 1:1,350,000(A3)
"Based on or contains data provided by the State of Queensland (Department of Environment and Resource Management) 2011. In consideration of the State permitting use of this data you acknowledge and
agree that the State gives no warranty in relation to the data (including accuracy, reliability,completeness, currency or suitability) and accepts no liability (including without limitation,
liability in negligence) for any loss, damage or costs (including consequential damage) relating toany use of the data. Data must not be used for direct marketing or be used in breach of the privacy laws."
Note: Every effort has been made to ensure this information is spatially accurate. The location ofthis information should not be relied on as the exact field location.
22/03/2013B
DATE:CREATED BY:
MAP NO:REV NO:MAP TYPE: Other
PLAN REF:CHECKED BY: NC
M_24969_07TG
v4
X Town/City
Cross Sections
QGC Field
Geology OutcropsCretaceous
Gubberamunda Sandstone
Westbourne Formation
Springbok Sandstone
Walloon Subgroup
Evergreen Sandstone
Hutton Sandstone
Precipice Sandstone
High Confidence Hydrochemical Facies BoundaryUpper Unit
Mixed
Na-Cl
Na-HCO3
Middle UnitMixed
Na-Cl
Na-HCO3
Lower UnitMixed
Na-Cl
Na-HCO3
0 25 50 75
X
X
X
X
X
XX
X
X
X
X
X
X
X
X
X
X
X
X XX
XX
X
XX
X
XX
X
X
X
X
X
X
X XX
X
X
X
X
G
F
E
D
C
B
A
G'
F'
E'
D'
C'
B'
A'
ROMA
TARA
BELL
SURAT
OAKEY
DALBY
MILES
TAROOM
INJUNE
YULEBADULACCA
WANDOAN
GAYNDAH
PROSTON
MITCHELL
EIDSVOLD
JANDOWAE
THEODORE
ST GEORGE
INGLEWOOD
MUNDUBBERA
PITTSWORTH
MILLMERRAN
CHINCHILLA
WALLUMBILLA
CECIL PLAINS
Lila
JenWill
AlexCam
Kate
Sean
Ross Carla
Arvin
Harry
Owen
David
Codie
Acrux
Grace
Teviot
Justin
Myrtle
Peebs
Kenya
Clunie
Poppy
Argyle
Cassio
Lauren
Jordan
Polaris
Barney
Lawton
Marcus
Connor
Celeste
Andrew
RubyJo Isabella
Mamdal
Jammat
McNulty
Cougals
Michelle
Bellevue
Kathleen
Margaret
Aberdeen
Pinelands
Maire Rae
Glendower
Ridgewood
Kenya East
Broadwater
Berwyndale
Avon Downs
Matilda-John
Woleebee Creek
Paradise Downs
Berwyndale South
Regional Hydrochemical StudyHydrochemical Facies of Upper, Middle and Lower
Units Combined
±0 25 50 75 100
Kilometers
DATA SOURCE: Towns - GAWaterbores - DNRM
Map Projection: GDA 94 SCALE: 1:1,350,000(A3)
"Based on or contains data provided by the State of Queensland (Department of Environment and Resource Management) 2011. In consideration of the State permitting use of this data you acknowledge and
agree that the State gives no warranty in relation to the data (including accuracy, reliability,completeness, currency or suitability) and accepts no liability (including without limitation,
liability in negligence) for any loss, damage or costs (including consequential damage) relating toany use of the data. Data must not be used for direct marketing or be used in breach of the privacy laws."
Note: Every effort has been made to ensure this information is spatially accurate. The location ofthis information should not be relied on as the exact field location.
22/03/2013B
DATE:CREATED BY:
MAP NO:REV NO:MAP TYPE: Other
PLAN REF:CHECKED BY: NC
M_24969_07TG
v4
X Town/City
Cross Sections
QGC Field
Geology OutcropsCretaceous
Gubberamunda Sandstone
Westbourne Formation
Springbok Sandstone
Walloon Subgroup
Evergreen Sandstone
Hutton Sandstone
Precipice Sandstone
High Confidence Hydrochemical Facies BoundaryUpper Unit
Mixed
Na-Cl
Na-HCO3
Middle UnitMixed
Na-Cl
Na-HCO3
Lower UnitMixed
Na-Cl
Na-HCO3
100
Figure 9-3 – Hydrochemical facies of upper, middle and lower units combined
152
9.5 MAJOR ION RESULTS
9.5.1 HYDROCHEMICAL FACIES
The concept of hydrochemical facies was given prominence by Back (1961) and has been successfully used to map
groundwater types spatially and with depth. The facies groups are derived from the normalised milliequivalent
values for the major ions in solution (Na, K, Ca, Mg, Cl, HCO3 and SO4).
Hydrochemical facies provide a superior method of characterising the distribution of major ion groundwater
character as opposed to the mapping of isopleths. The latter method displays the distribution of only one
parameter, whereas the mapping of hydrochemical facies shows the interdependencies of the major ions
controlling groundwater character.
Hydrochemical facies were mapped by creating three groups of stratigraphic units: the Upper units (Cretaceous,
Gubberamunda Sandstone and Westbourne Formation), the Middle units (Springbok Sandstone and Walloon
Subgroup) and the Lower units (Hutton Sandstone, Evergreen Formation, Precipice Sandstone and Base Jurassic).
These categories logically group the non-productive formations below the Walloon Subgroup, combine the
Walloon Subgroup with the Springbok Sandstone, which is considered to be the most sensitive formation to
impacts from CSG production in the Walloon Subgroup, and combine the formations above the Springbok
Sandstone.
The rationale for subdividing the stratigraphy into three zones was based on the following:
• The Eurombah Formation has been characterised as an effective aquitard at the base of the Walloon
Subgroup above the underlying Hutton Sandstone and major ion groundwater character is generally different
above and below this interface. The Hutton Sandstone and underlying units are considered the lower
potentially impacted zone in the context of the hydrochemical zones adopted.
• There is no formally recognised low permeability unit equivalent to the Eurombah Formation between the
Walloon Subgroup and the overlying Springbok Sandstone. The mineral composition of the both units is
similar and coals of similar thickness to those in the Walloon Subgroup are known to exist in the Springbok
Sandstone. Major ion groundwater geochemical character is also similar in both stratigraphic units as shown
on Durov and bivariate major ion molar ratio plots. Although mineralogically the Westbourne Formation has a
similar composition to both the Walloon Subgroup and the Springbok Sandstone, the groundwater character
is typically different and the rock framework-matrix textural relationships provide for a generally tighter gross
permeability than exhibited by the Springbok Sandstone. The Westbourne Formation, therefore, potentially
provides a more effective aquitard dividing the overlying Jurassic-Cretaceous succession from the Walloon
Subgroup and the Springbok Sandstone, the former being considered the upper potentially impacted zone.
The groundwater system throughout this region is characterised by two major ion hydrochemical facies: sodium-
bicarbonate (Na-HCO3) and sodium-chloride (Na-Cl).
Figure 9-3 presents the hydrochemical facies for all units combined. These results show a number of mixed
zones along the north-west/southeast cross-section A-A’, a Na-Cl dominance along the northern and eastern
boundaries of this section and a Na-HCO3 dominance toward the centre and west of the region.
The grouped hydrochemical facies displayed in Figure 9-3 and 9-4 were also plotted vertically along cross-section
A-A’ with bores located proximal to this line (Figure 9-3). This shows Na- HCO3 water dominating in the northwest
toward the primary basin recharge area where the Middle and Lower units outcrop.
The Upper units display predominantly Na-Cl or mixed facies. This mix of facies continues in the south-east
Middle and Lower units with the Na- HCO3 facies dominating again in the deepest units toward the centre of the
cross-section.
153
QGC is establishing an extensive monitoring bore network in the Surat Basin.
154
500
1,500
0
1,000
2,000
0
Dep
th (m
bgl
)
500 1,000
Na+ (mg/I)
Na+ vs DepthNa+ (mg/l)
1,500 2,000 2,500 3,000 3,500 4,000
Depth Charts
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
0
500
1000
1500
2000
0 500 1000 1500 2000 2500 3000 3500 4000
Dep
th (m
bgl
)
Na+ (mg/l) Na+ vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
0
200
400
600
800
1000
1200
1400
1600
0 1000 2000 3000 4000 5000 6000
Dep
th (m
bgl
)
Cl- (mg/l) Cl- vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B)
0
500
1000
1500
2000
0 500 1000 1500 2000
Dep
th (m
bgl
)
HCO3 (mg/l) HCO3 vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM)
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000 10000 12000 14000
Dep
th (m
bgl
)
TDS (mg/l) Salinity vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
500
1,500
0
1,000
2,000
0
Dep
th (m
bgl
)
500 1,000
HCO3 (mg/I)
HCO3 vs DepthHCO3 (mg/I)
1,500 2,000
Depth Charts
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
0
500
1000
1500
2000
0 500 1000 1500 2000 2500 3000 3500 4000
Dep
th (m
bgl
)
Na+ (mg/l) Na+ vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
0
200
400
600
800
1000
1200
1400
1600
0 1000 2000 3000 4000 5000 6000
Dep
th (m
bgl
)
Cl- (mg/l) Cl- vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B)
0
500
1000
1500
2000
0 500 1000 1500 2000
Dep
th (m
bgl
)
HCO3 (mg/l) HCO3 vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM)
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000 10000 12000 14000
Dep
th (m
bgl
)
TDS (mg/l) Salinity vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
Depth Charts
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
0
500
1000
1500
2000
0 500 1000 1500 2000 2500 3000 3500 4000
Dep
th (m
bgl
)
Na+ (mg/l) Na+ vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
0
200
400
600
800
1000
1200
1400
1600
0 1000 2000 3000 4000 5000 6000
Dep
th (m
bgl
)
Cl- (mg/l) Cl- vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B)
0
500
1000
1500
2000
0 500 1000 1500 2000
Dep
th (m
bgl
)
HCO3 (mg/l) HCO3 vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM)
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000 10000 12000 14000
Dep
th (m
bgl
)
TDS (mg/l) Salinity vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
CretaceousGubberamunda SST (DNRM)Springbok SST (B)Walloon Subgroup (B)Hutton SST (B)Precipice SST (B)
Gubberamunda SST (B)Westbourne FM (B)Springbok SST (MB)Walloon Subgroup (CSG)Hutton SST (DNRM)Precipice SST (DNRM)
Gubberamunda SST (MB)Westbourne FM (DNRM)Springbok SST (DNRM)Walloon Subgroup (DNRM)Evergreen FM (B)Base Jurassic (B)
Depth Charts
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
0
500
1000
1500
2000
0 500 1000 1500 2000 2500 3000 3500 4000
Dep
th (m
bgl
)
Na+ (mg/l) Na+ vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
0
200
400
600
800
1000
1200
1400
1600
0 1000 2000 3000 4000 5000 6000
Dep
th (m
bgl
)
Cl- (mg/l) Cl- vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B)
0
500
1000
1500
2000
0 500 1000 1500 2000
Dep
th (m
bgl
)
HCO3 (mg/l) HCO3 vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM)
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000 10000 12000 14000
Dep
th (m
bgl
)
TDS (mg/l) Salinity vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
Depth Charts
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
0
500
1000
1500
2000
0 500 1000 1500 2000 2500 3000 3500 4000
Dep
th (m
bgl
)
Na+ (mg/l) Na+ vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
0
200
400
600
800
1000
1200
1400
1600
0 1000 2000 3000 4000 5000 6000
Dep
th (m
bgl
)
Cl- (mg/l) Cl- vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B)
0
500
1000
1500
2000
0 500 1000 1500 2000
Dep
th (m
bgl
)
HCO3 (mg/l) HCO3 vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM)
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000 10000 12000 14000
Dep
th (m
bgl
)
TDS (mg/l) Salinity vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
155
Figure 9-5 – Na, Cl and HCO3 trends with depth (west)
CI- vs DepthCI- (mg/l)
1,600
0
Dep
th (m
bgl
)
1,000
CI- (mg/l)
2,000 3,000 4,000 5,000 6,000
1,400
1,200
1,000
800
600
400
200
0
Depth Charts
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
0
500
1000
1500
2000
0 500 1000 1500 2000 2500 3000 3500 4000
Dep
th (m
bgl
)
Na+ (mg/l) Na+ vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
0
200
400
600
800
1000
1200
1400
1600
0 1000 2000 3000 4000 5000 6000
Dep
th (m
bgl
)
Cl- (mg/l) Cl- vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B)
0
500
1000
1500
2000
0 500 1000 1500 2000
Dep
th (m
bgl
)
HCO3 (mg/l) HCO3 vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM)
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000 10000 12000 14000
Dep
th (m
bgl
)
TDS (mg/l) Salinity vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
Salinity vs DepthTDS (mg/l)
1,600
0
Dep
th (m
bgl
)
2,000
CI- (mg/l)
4,000 6,000 8,000 10,000 12,000
1,400
1,200
1,000
800
600
400
200
0
Depth Charts
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
0
500
1000
1500
2000
0 500 1000 1500 2000 2500 3000 3500 4000
Dep
th (m
bgl
)
Na+ (mg/l) Na+ vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
0
200
400
600
800
1000
1200
1400
1600
0 1000 2000 3000 4000 5000 6000
Dep
th (m
bgl
)
Cl- (mg/l) Cl- vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B)
0
500
1000
1500
2000
0 500 1000 1500 2000
Dep
th (m
bgl
)
HCO3 (mg/l) HCO3 vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM)
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000 10000 12000 14000
Dep
th (m
bgl
)
TDS (mg/l) Salinity vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
12,000
Depth Charts
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
0
500
1000
1500
2000
0 500 1000 1500 2000 2500 3000 3500 4000
Dep
th (m
bgl
)
Na+ (mg/l) Na+ vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
0
200
400
600
800
1000
1200
1400
1600
0 1000 2000 3000 4000 5000 6000
Dep
th (m
bgl
)
Cl- (mg/l) Cl- vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B)
0
500
1000
1500
2000
0 500 1000 1500 2000
Dep
th (m
bgl
)
HCO3 (mg/l) HCO3 vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM)
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000 10000 12000 14000
Dep
th (m
bgl
)
TDS (mg/l) Salinity vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
CretaceousGubberamunda SST (DNRM)Springbok SST (B)Walloon Subgroup (B)Hutton SST (B)Precipice SST (B)
Gubberamunda SST (B)Westbourne FM (B)Springbok SST (MB)Walloon Subgroup (CSG)Hutton SST (DNRM)Precipice SST (DNRM)
Gubberamunda SST (MB)Westbourne FM (DNRM)Springbok SST (DNRM)Walloon Subgroup (DNRM)Evergreen FM (B)Base Jurassic (B)
Depth Charts
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
0
500
1000
1500
2000
0 500 1000 1500 2000 2500 3000 3500 4000
Dep
th (m
bgl
)
Na+ (mg/l) Na+ vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
0
200
400
600
800
1000
1200
1400
1600
0 1000 2000 3000 4000 5000 6000
Dep
th (m
bgl
)
Cl- (mg/l) Cl- vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B)
0
500
1000
1500
2000
0 500 1000 1500 2000
Dep
th (m
bgl
)
HCO3 (mg/l) HCO3 vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM)
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000 10000 12000 14000
Dep
th (m
bgl
)
TDS (mg/l) Salinity vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
Depth Charts
Observations: Na, Cl and TDS significantly decline below 200 m depth decrease with depth, with the exception of the Walloon Subgroup, particularly the CSG samples. HCO3 concentrations are in similar range (0 – 1,000 mg/l) across all depths with concentrations up to 2000 mg/l near the surface in the Gubberamunda SST and 2200 mg/l in the Walloon Subgroup CSG samples between 600 and 900 m depth. HCO3 concentrations increase with depth for the Hutton SST and Precipice SST.
0
500
1000
1500
2000
0 500 1000 1500 2000 2500 3000 3500 4000
Dep
th (m
bgl
)
Na+ (mg/l) Na+ vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
0
200
400
600
800
1000
1200
1400
1600
0 1000 2000 3000 4000 5000 6000
Dep
th (m
bgl
)
Cl- (mg/l) Cl- vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B)
0
500
1000
1500
2000
0 500 1000 1500 2000
Dep
th (m
bgl
)
HCO3 (mg/l) HCO3 vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM)
0
200
400
600
800
1000
1200
1400
1600
0 2000 4000 6000 8000 10000 12000 14000
Dep
th (m
bgl
)
TDS (mg/l) Salinity vs Depth
Cretaceous (B) Gubberamunda SST (B) Gubberamunda SST (MB) Gubberamunda SST (DNRM) Westbourne FM (B) Westbourne FM (DNRM) Springbok SST (B) Springbok SST (MB) Springbok SST (DNRM) Walloon Subgroup (B) Walloon Subgroup (CSG) Walloon Subgroup (DNRM) Hutton SST (B) Hutton SST (DNRM) Evergreen FM (B) Precipice SST (B) Precipice SST (DNRM) Base Jurassic (B)
156
9.5.2 CONCENTRATIONS WITH DEPTH
Figure 9-5 shows the concentrations of Na and Cl with bore total depth. The depth graphs for these areas show
similar patterns and trends. In general a linear correlation occurs between Na, Cl and total dissolved solids (TDS).
A summary of the Na, Cl and TDS data trends in the North and South is as follows:
• In the North, most of the data points have total depths of <400 m depth below ground level;
• The Lower units (particularly the Precipice Sandstone and Base Jurassic), for which there is limited data, show
the lowest concentrations of Na, Cl and TDS;
• The Walloon Subgroup and Gubberamunda Sandstone samples have the highest concentrations, with the
Gubberamunda Sandstone samples showing a decrease in concentration with depth;
• In the South, with more data points, most of the data points are from bores of <200 m total depth:
• There are higher concentrations of both Na and Cl generally, particularly in the Walloon Subgroup
samples;
• Within the 0 to 200 m depth zone, Na, Cl and TDS concentrations are higher from the Springbok
Sandstone and Walloon Subgroup samples compared to the Cretaceous units, Gubberamunda Sandstone
and Westbourne Formation samples;
• The limited number of Hutton Sandstone samples in this depth zone shows a range of concentrations of
these parameters;
• The majority of the data points that extend beyond 200 m to >800 m depth occur in the Gubberamunda
Sandstone and Walloon Subgroup. Generally, the concentrations of Na, Cl and TDS are lower with depth in
the Gubberamunda Sandstone samples; and
• Although the Springbok Sandstone data does not extend beyond 400 m in this area, the Springbok
Sandstone data is showing a similar decline in concentration with depth in Na, Cl and TDS;
• There is a larger quantity of deeper bore samples in this area owing to the deeper geological units here. A
large majority of the samples (50 out of 63) are from the Gubberamunda Sandstone, from bores with total
depths ranging from 64 m to 1,511 m;
• 53 out of 63 of the data points in this region are of Na-HCO3 water type; and
• Nearly all of the Na-Cl water type samples (nine out of ten) are from Gubberamunda Sandstone samples.
9.5.3 XY PLOTS
The results presented on XY plots grouped by their hydrochemical facies show in more detail the spatial
relationships of their primary components. The molar equivalent concentrations of the major ions are presented
for each vertical unit group (Upper units, Middle units, Lower units) for each lateral area (North, South, West).
Figure 9-6 shows the XY plots of Na vs. Cl for the Na-Cl hydrochemical facies for each of the Upper (Cretaceous,
Gubberamunda Sandstone, Westbourne Formation), Middle (Springbok Sandstone, Walloon Subgroup) and
Lower units (Hutton Sandstone, Evergreen Formation, Precipice Sandstone, Base Jurassic). These plots display the
following characteristics:
• The majority of available data points occur in the Middle units where there is an increased concentration of
Na and Cl from the North to the South but a consistent 1:1 relationship between Na and Cl concentrations
for these samples. This agrees with a similar pattern noted in the previous depth comparison for the Walloon
Subgroup samples;
• The Middle and Lower units’ X-Y plots of Na vs. Cl are zoomed in for a closer display of the data points and
exclude two and one data points, respectively, of greater Na and Cl concentrations that are near to the same
trend line relationships. The Upper and Lower units, with much fewer data points in the Na-Cl facies, show
slightly higher concentrations of Na in relation to Cl, closer to a 1.25:1 trend line relationship; and
• In the Upper units, this relationship of higher Na is largely driven by the West samples as the North and South
samples have Na and Cl concentrations nearer a 1:1 relationship.
157
Figure 9-6 – X-Y Na, Cl plots for Na-Cl hydrochemical facies for the upper, middle and lower units
90
80
60
40
20
70
50
30
10
0
0
Na+
in fl
uid
(mm
oI/I
) 100
110
120
130
140
150
160
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180
CI- in fluid (mmoI/I)
Upper Units Na+ vs CI-
220 240
180
160
120
80
40
140
100
60
20
0
0
200
20 40 60 80 100 120 140 160 180 200
CI- in fluid (mmoI/I)
Middle Units Mixed Na+ vs CI-
Na+
in fl
uid
(mm
oI/I
)
North samples South samplesWest samples
1:25:1
North samples South samplesWest samples
1:1
158
Figure 9-7 – X-Y Na, Cl plots for Na-Cl hydrochemical facies for the upper, middle and lower units
9.6 GROUNDWATER ISOTOPIC ANALYSIS
Both radiogenic and stable environmental isotopes in groundwater provide valuable insights into:
• groundwater recharge provenance;
• groundwater residence times;
• contributions to groundwater compositional evolution from water-rock and gas-rock interactions;
• gas generation processes;
• groundwater mixing trends; and
• flux magnitude across hydraulic boundaries.
Groundwater samples for isotopic analysis (δD, δ18O δ13 14C 14C, 36Cl, 87Sr/86Sr) were collected from the 12 Phase I
groundwater monitoring wells completed in the Gubberamunda Sandstone and the Springbok Sandstone.
Three main types of analysis were used to interpret the isotopic suite:
• Spatial enrichment4 and depletion trends;
• Enrichment and depletion trends with depth; and
• Inter-isotope relationships.
36
32
24
16
8
28
20
12
4
0
0
Na+
in fl
uid
(mm
oI/I
)
40
44
48
52
56
60
64
4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64
CI- in fluid (mmoI/I)
Lower Units1 Na+ vs CI-
68
72
North samples South samplesWest samples
1.25:1
159
The interpretations derived from the above analyses were combined with the interpretation of major and
minor ion solute relationships to further explore the hypotheses developed to explain the processes governing
groundwater compositional evolution.
The results for delta deuterium (δD) and delta 18 oxygen (δ18O) plotted against the Global Meteoric Water
Line (GMWL – δD = 8.13 x δ18O + 10.8) and the Brisbane meteoric water line (BMWL - δD = 7.7 x δ18O + 12.6,
Lamontagne, 2011) show two overlapping clusters, with the exception of one data point for the Springbok
Sandstone (Figure 9-8). Linear trends show reasonably good correlations (R2 of 0.767 and 0.8937), however; the
data points are tightly clustered. The data plot close to the GMWL and a slight evaporation trend is evident in the
data from the Gubberamunda Sandstone. The data from the Springbok Sandstone shows a trend sub-parallel to
the GMWL.
4 Enrichment is a process by which the relative abundance of the isotopes of a given element is altered, thus producing a form of the element that has been
enriched in one particular isotope. Enrichment in one isotope implies depletion in its other isotopic forms.
VSMOW – Vienna Standard Mean Ocean Water standard (GMWL, Craig, 1961)
Figure 9-8 – Groundwater δD and δ18O ratios in relation to the Global Meteoric Water Line
δ18O ‰ VSMOW
-40
-50
-7
δD ‰
VSM
OW
-30
-6 -5
KEE GW4 SP
KEE GW2 SP
LRN GW2 SP
BWS GW2 SPKEE GW3 GU
PPY GW2 SP
LRN GW1 GUBWS GW1 GU
KEE GW1 GU
WCK_GW1 GU
GMWLy = 8.13x + 10.8
BEL GW2 SP
BMWLy = 7.7x + 12.6
160
9.7 PRELIMINARY GEOCHEMICAL MODELLING
The variation in groundwater character both spatially and with depth provides the basis for developing
hypotheses to explain hydrochemical evolution in relation to groundwater flow vectors and residence times. A
number of hypotheses are presented and details of how it is intended to test the concepts are also provided. Two
topics of particular interest are the hydrochemical composition of groundwater associated with CSG reservoirs
and the vertical interaction between aquifers overlying and underlying CSG reservoirs. Both these areas are of
interest from groundwater resource management and CSG production perspectives.
An analysis of the spatial distribution of calcium, magnesium and sulphate in groundwater in the Surat Basin
is presented in this report. The hydrochemical signatures show a different association between CSG reservoirs
and groundwater when compared to the CSG production areas in the United States. Low concentrations of these
analytes in groundwater are indicative of prospective CSG bearing formations in the USA. Low values for these
aqueous components in the Surat Basin show no equivalent affinity and are characteristic of groundwater from
most areas in all the formational units.
The data have been evaluated statistically, spatially and in geological context to provide a holistic interpretation
of the distribution of groundwater character. A typical groundwater geochemical maturity pattern which may
operate in the Surat Basin consists of: increasing Na:Cl ratios, stabilising Cl- concentrations, increasing HCO3-
concentrations and increasing total dissolved solids. There are a number of water-rock and water-gas reactions
contributing to this general pattern of groundwater evolution. However, the incongruent dissolution of albite and
crystallisation of kaolinite and the net product of carbonate mineral dissolution and precipitation are currently
the most favoured hypotheses. Figure 9-9 illustrates this evolution pathway.
Figure 9-9 – Conceptual reaction path model for the evolution of groundwater from Na-Cl to Na-HCO3 hydrochemical facies
Evolution from Na-CI
hydrochemical facies
Meteoric Recharge
(composition unknown: may
contain Na-CI
aerosols)
Dissolution of Halite
in the vadrose zone
NaCI à Na- + CI-
Na-CI groundwater
enters the phreatic zone
Dissolution of
gypsum
CaSO4 - 2H2O à 2H2O +Ca++ + SO4
Addition of Ca++ and SO4 -
to solution
Dissolution of organic matter producing CO2
CH2COO- + O2(aq) à HCO3- + CO2(aq) +
H2ODrop in pH
Dissolution of carbonate
minerals
CaCO3 + CO2(aq) + H2O à Ca++ + 2HCO3 -
CaMg(CO3)2 + 2CO2(aq) + 2H2O à Mg++ + Ca++ +
4HCO3- FeCO3 + CO2(aq) + H2O àFe++ + 2HCO3-
Addition of Ca++, Mg++ Fe++
and HCO3 to solution
Increase in pH
Groundwater supersaturated
with respect to carbonate
minerals
Removal of Ca++ and Mg++ from solution
by cation exchange with
Na+
Incongruent albite hydrolysis - addition
of aqueous Na+
HCO3 and SiO2 to solution and
clay mineral precipitation
2NaAISi3O2 + 2CO2(aq) +3H2O à2Na+
+AI2Si2O2(OH)4 +4SiO2(aq) + 2HCO3-
Enrichment of Na relative to CI increase in
HCO3- increase in TDS
CI- concentration
plateaus
Evolution to Na-HCO3-
hydrochemical facies
Increasing Total Dissolved Solids (TDS)
161
A hypothesis is presented for a recharge pathway in relation to the Springbok Sandstone aquifer within the
QGC Surat Basin development areas. Modelling of regional groundwater flow vectors indicates convergence of
recharge from the northwest and southeast of the basin and discharge to both the northeast and southwest.
Groundwater samples analysed from the Springbok Sandstone, Gubberamunda Sandstone and Walloon
Subgroup are of Na-HCO3 hydrochemical facies, whereas groundwater proximal to the recharge zones is of Na-Cl
facies. Groundwater monitoring bores and CSG wells used in the ongoing studies are located approximately
10-20 km from outcropping units to the northeast. Based on the results of regional modelling, however; these
areas form a groundwater discharge zone to the Dawson River catchment (QGC 2013c). Geochemical modelling
simulations were conducted to evaluate both the long and short distance recharge pathways to the monitoring
and production areas. The simulations consider the observed hydrochemical composition of groundwater in the
recharge areas and incorporate mineral data in reaction path models used to understand the impact of water-
rock interactions along the flow paths. The state of equilibrium apparent between the groundwater and the
aquifer media is incorporated to establish the most probable reactions taking place.
Isotopic data collected from the Springbok Sandstone and Gubberamunda Sandstone aquifers were incorporated
with major and minor ion hydrochemistry to generate hypotheses to understand inter-aquifer behaviour. Isotope
fractionation processes that could potentially control the observed signatures in groundwater were presented in
the Stage 2 WMMP Preliminary Regional Hydrochemistry Characterisation Report (2013). Model simulations are
based on assumptions regarding mineral isotopic signatures, which are to be verified or refuted when new data
is available in the future. The methodology developed using the information from the Springbok Sandstone and
the Gubberamunda Sandstone will be applied to other aquifer pairs in the future (e.g. the Hutton Sandstone and
the Walloon Subgroup and the Walloon Subgroup and the Springbok Sandstone). An integrated approach using
hydrochemical, mineral and isotopic data in conjunction with geochemical modelling, spatial analysis and an
appropriate geological context provides a robust and holistic interpretation of subsurface fluid behaviour.
The spatial analysis and statistical treatment applied to the subordinate major ions in groundwater across the
Surat Basin show that there are not any clear associations with coal bearing units in the succession. The low
concentrations associated with CSG prospective regions in the United States sedimentary basins are largely
derived from cycling between marine and terrestrial depositional systems. This cyclicity is not evident in the
Surat Basin and the succession is dominated by terrigenous clastic deposits. Sources of sulphate are very limited
in non-marine strata and the ubiquitous occurrence of siderite and lack of sulphide minerals in the Jurassic
strata of the Surat Basin demonstrates that low sulphate aqueous systems have predominated for a protracted
period of time. The range in relative subordinate minor ion concentrations shows a similar pattern in the Walloon
Subgroup, Springbok Sandstone and the Gubberamunda Sandstone. These units exhibit a range of deposits from
very low energy coal swamp to high energy braided fluvial systems from the Walloon Subgroup up through to the
Gubberamunda Sandstone. Similar hydrochemical trends for this group of ions are also apparent in the Precipice
Sandstone, Evergreen Formation and Hutton Sandstone (Appendix H).
The second phase of reaction path modelling shows that a combination of water-rock/gas-water reactions and
fluid-fluid mixing can explain groundwater evolution associated with the interpreted regional groundwater
flow vectors. Meteoric recharge enters the groundwater system and reacts with ephemeral evaporite minerals
in the vadose zone, which imparts a Na-Cl major ion character to the groundwater. Silicate rock weathering and
carbonate dissolution reactions contribute Na+, Ca2+, Mg2+ and HCO3- ion to solution increasing the
HCO3-:Cl- and Na+:Cl- ratios. Mixing with less saline Na-HCO3 dominated groundwater along the interpreted
regional flow paths provides a mechanism for the observed change in hydrochemical facies from the Bellevue
field to the Lauren field. The primary physico-chemical parameters show good agreement between the modelled
and observed values for the Berwyndale South field. Further refinement of the model outputs could be made by
introducing kinetic rate laws for the applicable reactions and it is planned to provide a comprehensive treatment
of data by constructing reactive transport models in future work.
162
9.8 SUMMARY OF RESULTS
The initial results show:
• A number of Na-Cl dominant and Mixed (i.e. both Na- HCO3 and Na-Cl) zones in the Upper and Middle units
in the north-central and south-east of the study area;
• A Na-HCO3 water type is prevalent in the north-west (where the Lower units outcrop near the basin’s primary
recharge area) and toward the deepest units in the centre and west of the study area that dip toward the
Mimosa Syncline;
• While the groundwater entering the study area from the south-east has Na-Cl and mixed facies, as this water
travels west to south-west and down dip and comes into contact with the dominant Na- HCO3 water and Na-
HCO3 prevalence persists;
• Piper and Durov diagrams of the data corroborate these observations, showing higher percentages of Cl in the
North and South and of HCO3 in the West;
• Most of the data analysed show low concentrations of Mg, Ca and SO4 across the study area for both the
Na-Cl and Na- HCO3 major hydrochemical facies types;
• A linear correlation is evident between Na, Cl and total dissolved solids (TDS) in the North and South with
concentrations generally decreasing with depth and the lowest concentrations occurring in the Lower units;
• There is generally an increase in HCO3 with depth. In the West, a linear correlation is evident between Na,
HCO3 and TDS, increasing with depth for all formations;
• At a regional scale, the Walloon Subgroup is clearly dominated by a 1:1 Na-Cl relationship, although
bicarbonate enrichment is evident in some areas (e.g. the Lauren and Berwyndale South fields in the QGC
central development area);
• A sodium enrichment relative to chloride occurs in the Middle and Lower units with Na-Cl water type;
• Most samples in the West with a Na-HCO3 water type are from the Gubberamunda Sandstone and have a
molar relationship of 1.5 Na to 1 HCO3. A slightly lower Na:HCO3 ratio occurs in the Lower and Middle unit Na-
HCO3 facies (1.25:1);
• Groundwater recharge, occurring along the formation outcrops extending across and north-east of the
QCLNG tenements, may mobilise salts stored within the vadose zone of the shallow subsurface creating
mixed zones of Na-Cl, Na-HCO3 and mixed facies along the North and South areas near these outcrops.
Groundwater from these zones flows both north/north-east and south/south-west. A Na-HCO3 facies begins
to dominate along flow paths down dip, into the deeper areas of the basin towards the Mimosa Syncline; and
• Analysis and interpretation of the isotopic data shows that there are a number of processes contributing
to the distribution of groundwater character across the QCLNG study area. Relationships were identified
between different groups of isotopes and some clear trends are evident both spatially and with depth. The
preliminary interpretations indicate that the combination of hydrochemical and isotopic data could provide a
powerful tool for the investigation of inter-aquifer relationships to assist in forecasting the potential impacts
of CSG production activities.
The data trends observed in the current data set generally agree with other regional hydrochemical studies across
the GAB. Regional groundwater flows are described as increasing in Na, HCO3 and TDS from east to west with the
south-west GAB having an increased SO4 signature. Cl is conserved along groundwater flow paths throughout
most of the GAB, while there are ’systematic variations‘ in Cl concentrations across the GAB. GAB sub-basin
trends of increased alkalinity, specifically HCO3 alkalinity have been identified and increased Na excess (i.e. Na>Cl)
toward the basin centres. The current project data set also suggests a decrease in Cl concentrations with depth
whereas HCO3 concentrations increase with depth.
163
These trends along with the mapped hydrochemical facies and groundwater flow lines indicate that groundwater
recharge occurs along the formation outcrops extending across and northeast of the QCLNG tenements.
Broader strategic conclusions which this work suggests are:
• The significance of unsaturated zone and relatively shallow flow processes in influencing deeper flow
hydrochemistry. This suggests that relatively local flow processes may be significant in many situations;
• Even though horizontal flow dominates over vertical flow, vertical flow processes can be important in some
situations;
• Groundwater flow rates are generally very slow, although locally where high hydraulic gradients exist and
aquitard material is thin, greater flow rates are possible; and
• The environmental values of the groundwater generally span the drinking water, agriculture and aquatic
ecosystem protection ranges.
9.9 FURTHER WORK
Additional data to be collected in 2013/2014 combined with the existing data set will be used to test hypotheses
developed from the preliminary hydrochemistry characterisation and conceptual model. These hypotheses
include:
• The evolution of the facies zones primarily through discrete horizontal groundwater flow paths, rather than
through vertical flow;
• Can the source of Na-Cl at shallow depths be a consequence of salt influx (i.e. from the dissolution of salts in
the vadose zone)? This shallow Na-Cl signature evolves into Na- HCO3 as groundwater moves deeper into the
basin;
• The variation in hydrochemistry as a function of flow distance and aquifer medium mineralogy;
• Whether hydrochemical facies are altered as a result of the groundwater pumping from CSG activities by
increasing the rate of groundwater influx and shifting facies boundaries; and
• Whether hydrochemical signatures can be used to determine the quality of existing farm bores.
It is planned to collect further groundwater geochemical and isotopic data from the monitoring bore network
and pertinent mineral isotope data from drill core samples. The trends identified in this preliminary study will
be evaluated in relation to the processes postulated to control the distribution of hydrochemical character.
The hydrochemical framework combined with the isotopic analysis will be used to construct models to test
hypotheses in relation to implied groundwater flow and inter-aquifer relationships, particularly transfer rates
across flux boundaries.
Further hydrochemical assessments will be used to confirm the methodology used in threshold response plans
for groundwater chemistry, and to help identify flow mechanisms for MNES springs.
Available mineralogical data will be integrated with the groundwater facies and sub-facies mapping to better
understand the controls of the groundwater characteristics. The composition of framework and interstitial
minerals and the distribution of the reactive minerals will be used to refine the most probable water-rock
reactions.
164
The status of the Commitments relevant to hydrochemistry is as follows:
# Department Condition Description Completion date Status
Pre-Dec 2012 Post-Dec 2012
10 49bCompletion of preliminary hydrochemistry conceptual model. Justification of water quality trend indicators
April 2013
11 49b Completion of Isotope studies April 2013/April 2014
12 49b, 52d iiSubmission of integrated hydrochemistry report. Commitment to provide baseline definition of groundwater quality in the Northern Gas Fields
October 2014
62 49b Review and update of water quality trend indicatorsApril 2016 and thereafter at three-yearly intervals
Commitments completed Evergreen Commitments
Commitments work in progress Firm deliverables for that month