A preliminary hydrochemistry model and isotope assessment · 9.0 A preliminary hydrochemistry model...

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9.0 A preliminary hydrochemistry model and isotope assessment

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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.

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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.

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Figure 9-1 – Regional hydrochemical study sample type, formation and location

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Cross Section Lines

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!A Monitoring Bore - Springbok SST

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#* Baseline Sample - Cretaceous

# Baseline Sample - Gubberamunda SST

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# Baseline Sample - Walloon Subgroup

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_̂ 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

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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

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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)

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-400

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-800

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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

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OAKEY

DALBY

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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

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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

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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.

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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)

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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)

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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)

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Figure 9-5 – Na, Cl and HCO3 trends with depth (west)

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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)

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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


Middle Units Mixed Na+ vs CI-

Na+

in fl

uid

(mm

oI/I

)

North samples South samplesWest samples

1:25:1


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


Lower Units1 Na+ vs CI-

68

72


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

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