1.5.2.2 Groundwater


This product provides a baseline assessment of groundwater quality in the Galilee subregion with a focus on salinity, and information on selected trace elements. Water quality is assessed against national guidelines provided by the National Health and Medical Research Council (NHMRC/NRMMC, 2011) and the Australian and New Zealand Environment and Conservation Council (ANZECC/ARMCANZ, 2000).

Before an assessment of groundwater quality can be carried out it is necessary to have a conceptual understanding of hydrologic connectivity between different geological units. To assess the water quality of groundwater in the Eromanga and Galilee geological basins, which together comprise the subsurface geology of the Galilee subregion, geological units were grouped together into hydrogeologic units based on the current conceptual understanding of the hydrodynamics in the subregion (see companion product 1.1 for the Galilee subregion (Evans et al., 2014)). For the Eromanga Basin the hydrogeologic units determined are:

  • the Winton-Mackunda Formation – which was not grouped with other units
  • Allaru Mudstone, Toolebuc Formation and Wallumbilla Formation: an aquitard separating shallow aquifers from deeper confined systems. Referred to as the Allaru-Wallumbilla grouping
  • Wyandra Sandstone Member, Cadna-owie Formation, Hooray Sandstone: a confined aquifer. Referred to as the Wyandra-Hooray grouping
  • Westbourne Formation, Adori Sandstone, Birkhead Formation: an aquitard referred to as the Westbourne-Birkhead grouping
  • Hutton Sandstone, Boxvale Sandstone Member, Precipice Sandstone: a confined aquifer referred to as the Hutton-Precipice grouping
  • the Ronlow beds – which were not grouped with any other units
  • Cenozoic rocks – which were separated into basaltic and sedimentary units based on differences in water chemistry. These are referred to as Cenozoic-Basaltic Volcanics, and Cenozoic-Sediments respectively.

For the Galilee Basin the hydrogeologic units determined were:

  • the Clematis-Warang Sandstone – which was not grouped with any other units
  • the Betts Creek beds – which were not grouped with any other units
  • the Moolayember Formation – which was not grouped with any other units and is omitted from the summary below due to scarcity of data
  • Rewan Group – which was not grouped with any other units and is omitted from the summary below due to scarcity of data
  • Jochmus Formation, Jericho Formation and Aramac Coal Measures: a partial aquifer or leaky aquitard referred to as the Joe Joe Group.

Groundwater chemistry data for these hydrogeologic units were compiled from the Queensland groundwater bore database with some supplementary data from environmental impact statement (EIS) documents for coal developments in the Galilee Basin. Due to the potential for impacts on groundwater levels and quality to cross catchment divides, available groundwater data were considered for the entire subregion, rather than limiting the analysis to drainage boundaries within the subregion.

To assess the potential hazards associated with using groundwater in the subregion, groundwater chemistry data were compared to national guidelines for water quality in which a number of possible water uses were considered: human drinking water, stock drinking water and water for long-term irrigation (defined as up to 100 years).

Trigger values were taken from the Australian Drinking Water Guidelines (ADWG) (NHMRC/NRMMC, 2011) and the National Water Quality Management Strategy (NWQMS) (ANZECC/ARMCANZ, 2000).

Groundwater chemistry data were primarily collated from the Queensland groundwater database (Department of Natural Resources and Mines, 2014). This database contains data from bores drilled from the early 1890s through to the present. Over the decades there have been significant changes in how data from drill-holes are collected, as well as refinements in the general knowledge of the hydrogeology of the subregion. This can have implications for data quality.

In total, data for 5675 samples were available for the Galilee subregion. Of these, 4624 had sufficient stratigraphic data for a sample to be assigned to a hydrogeological unit. All samples had data for total dissolved solids (TDS), but only a fraction of samples had trace element analyses. The number of analyses for trace elements is discussed in Section 1.5.2.2.3.

1.5.2.2.1 Total dissolved solids

TDS trigger values were determined using ADWG values for human consumption and the NWQMS for stock water. The trigger values used for TDS are given in Table 12.

Table 12 Total dissolved solids trigger values


Water use

Total dissolved solids limit (mg/L)a

Source

Drinking water

1200

NHMRC/NRMMC (2011)

Stock

4000

ANZECC/ARMCANZ (2000, Table 4.3.1), upper limit for cattle with no adverse effects

aAssuming total dissolved solids is equal to 0.65 electrical conductivity

The range of TDS values in the dataset is shown in Table 13. The proportion of samples in exceedance of the different guidelines used can be seen in Table 14. TDS is highly variable in the subregion, with all hydrogeological units showing at least an order of magnitude difference between minimum and maximum values. Median values indicate that most groundwater in hydrogeologic units is appropriate for use as stock water, and water in many hydrogeologic units is appropriate for human consumption (on the basis of TDS). Relatively few units have a median below the threshold for irrigation water. Further discussion of the processes controlling TDS values and their implications will be provided in companion product 2.1 and companion product 2.3 for the Galilee subregion.

Table 13 Total dissolved solids range for hydrogeologic units in the Eromanga Basin and Galilee Basin sequences


Hydrogeologic unit

Minimum value (mg/L)

Maximum value (mg/L)

Mean

(mg/L)

Median

(mg/L)

Alluvium

59

8,292

1179

711

Cenozoic-Sediments

10

25,040

1426

880

Cenozoic-Basaltic Volcanics

364

4,091

894

782

Winton-Mackunda

79

20,400

3541

2917

Allaru-Wallambilla

170

12,735

2376

1222

Wyandra-Hooray

180

7,136

834

601

Westbourne-Birkhead

133

2,041

597

460

Ronlow beds

189

8,404

609

353

Hutton-Precipice

55

3,579

482

396

Clematis-Warang

103

3,290

574

471

Betts Creek beds

346

2,495

1078

951

Joe Joe Group

175

11,060

1607

928

Data: Bioregional Assessment Programme (Dataset 1)

Table 14 Total dissolved solids exceedance for hydrogeologic units in the Eromanga Basin and Galilee Basin sequences


Hydrogeologic unit

Number of samples

ADWGa exceedances (%)

Stock exceedances (%)

Alluvium

143

31%

6%

Cenozoic-Basaltic Volcanics

31

6%

3%

Cenozoic-Sediments

389

21%

6%

Winton-Mackunda

790

87%

34%

Allaru-Wallumbilla

240

52%

23%

Wyandra-Hooray

1303

25%

2%

Westbourne-Birkhead

274

15%

1%

Ronlow beds

289

8%

1%

Hutton-Precipice

870

7%

1%

Clematis-Warang

99

18%

8%

Betts Creek beds

128

30%

9%

Joe Joe Group

43

35%

12%

Total

4624

32%

9%

Data: Bioregional Assessment Programme (Dataset 1)

aAustralian Drinking Water Guidelines

1.5.2.2.2 Total dissolved solids distribution

Total dissolved solids data for groundwater from bores were used to generate salinity trend maps for the aquifer groups. TDS are routinely measured in the lab as part of a groundwater sample analysis. This differs from EC, which is often used as a measure of salinity in the field.

The salinity trend maps were generated using the ‘topo to raster’ interpolation method in ArcGIS. This is an iterative finite difference interpolation technique, which allows for surface continuity in sparse datasets. The available salinity data does not represent a single snapshot of water quality at a specific time; rather they provide a general indication of variations in salinity across the subregion. Furthermore, there is likely to be variations in quality of the sample analyses used to create the maps due to the archival nature of the data. Factors affecting archival data can include: use of different analysis methods; improvements in analyses technology over time; analysis accuracy and precision; variations in sample collection methodologies, and different bore construction techniques and quality. The archival nature of the data used means that temporal variation in water chemistry may contribute to the range of values seen in the TDS surfaces. However, the total variability in TDS for each hydrogeologic unit is at least one, and sometimes up to three, orders of magnitude difference, thus any temporal variations are likely to be minor in comparison to spatial variability.

As a quality control measure, some bore data were excluded from construction of these surfaces. Where a single bore had groundwater with high TDS that was anomalous in relation to other bores nearby, or where a single bore had high groundwater TDS with no controls nearby, these bores were excluded from generation of the TDS surfaces. Anomalously high TDS values may represent bores where stratigraphic or screened interval information are suspected to be incorrect, where sample contamination has occurred, or where there were errors in analysis.

Distribution of bores is often limited to within the vicinity of outcrop areas. Results may also be skewed in part through clustering of bores in areas where there is high production due to the presence of relatively fresh water, or alternatively areas with higher salinity are likely to have fewer bores to constrain interpolation. Interpretation of the TDS surfaces should be considered with these uncertainties in mind, and these maps should be treated as an image of regional trends in salinity for the hydrogeologic units in the subregion rather than a predictive tool for determining water quality where there is little bore coverage. It should also be noted that TDS for each hydrogeologic unit is displayed with a different colour gradient dependent on the range of TDS in each hydrogeologic unit, meaning direct comparisons between the maps cannot be made. Using a single scale for all maps would have allowed for comparison between the different hydrogeologic units, but the variability in TDS of the fresher units would not be visible due to the very high TDS values in more saline units.

Allaru-Wallumbilla grouping

Groundwater in the Allaru-Wallumbilla grouping is generally fresh in the north and central parts of the subregion, with some areas of higher salinity (up to 12,654 mg/L TDS) away from outcrop areas around Charleville and on the Maneroo Platform (Figure 13).

Figure 13

Figure 13 Allaru-Wallumbilla grouping total dissolved solids in the Galilee subregion

Data: Bioregional Assessment Programme (Dataset 2, Dataset 3)

Betts Creek beds

Bore distribution for the Betts Creek beds is largely limited to the eastern margin of the subregion where the Betts Creek beds and its correlatives outcrop (Figure 14). Away from the outcrop, groundwater quality data are generally only available from petroleum wells.

Figure 14

Figure 14 Betts Creek beds total dissolved solids surface for the Galilee subregion

Data: Bioregional Assessment Programme (Dataset 2, Dataset 3)

Clematis-Warang Sandstone

Groundwater in the Clematis-Warang Sandstone is generally fresh to brackish, with an area of higher salinity in the central part of the subregion, just east of Aramac (Figure 15).

Figure 15

Figure 15 Clematis-Warang Sandstone total dissolved solids surface for the Galilee subregion

Data: Bioregional Assessment Programme (Dataset 2, Dataset 3)

Hutton-Precipice grouping

Groundwater in the Hutton-Precipice grouping is generally fresh around recharge areas along the eastern margin of the aquifer extent. Higher salinity groundwater occurs in deeper parts of the aquifer system, around the western margin of the Galilee subregion, or the vicinity of the Maneroo Platform (Figure 16).

Figure 16

Figure 16 Hutton-Precipice grouping total dissolved solids surface for the Galilee subregion

Data: Bioregional Assessment Programme (Dataset 2, Dataset 3)

Westbourne-Birkhead grouping

Groundwater in the Westbourne-Birkhead grouping is relatively fresh near recharge areas around the eastern margin, with higher salinity areas occurring to the west, on the Maneroo Platform, and in the north of the subregion (Figure 17). Small saline areas, for example in the south-east, around single bores may be due to mis-assigned bores, sample contamination or inter-aquifer leakage.

Figure 17

Figure 17 Westbourne-Birkhead grouping total dissolved solids surface for the Galilee subregion

Data: Bioregional Assessment Programme (Dataset 2, Dataset 3)

Winton-Mackunda Formation

Groundwater in the Winton-Mackunda Formation has variable TDS, with higher salinities occurring around the Maneroo Platform and in the south of the subregion (Figure 18).

Figure 18

Figure 18 Winton-Mackunda Formation total dissolved solids surface for the Galilee subregion

Data: Bioregional Assessment Programme (Dataset 2, Dataset 3)

Wyandra-Hooray grouping

Groundwater in the Wyandra-Hooray grouping is generally fresh, with areas of higher salinity in the Maneroo Platform (Figure 19). Small areas of higher salinity centred on single bores may be due to mis-assigned bores, sample contamination or inter-aquifer leakage.

Figure 19

Figure 19 Wyandra-Hooray grouping total dissolved solids surface for the Galilee subregion

Data: Bioregional Assessment Programme (Dataset 2, Dataset 3)

1.5.2.2.3 Trace elements

Exceedances for the trace elements available in the dataset were determined using the ADWG for human consumption (National Health and Medical Research Council, 2011) and for stock water using trigger values in the NWQMS (ANZECC, 2000). Trace element trigger values and number of exceedances in the dataset are summarised in Table 15.

Table 15 Number of analyses and exceedances for trace elements in groundwater of Eromanga and Galilee basins


Parameter

Number of analyses

Fraction in exceedance of guidelines

(%)

Minimum value (mg/L)

Maximum value (mg/L)

ADWGa trigger

(mg/L)

Stock triggerb

(mg/L)

Silver (Ag)

6

0%

0.001

0.003

0.00002

na

Aluminium (Al)

1075

3%

bdc

0.5

0.2d

5

Arsenic (As)

49

100%

0.001

0.3

0.001

0.0005

Boron (B)

1118

24%

bd

13.8

4

5

Cadmium (Cd)

3

0%

0.0001

0.0003

0.002

0.01

Cobalt (Co)

18

6%

0.001

0.062

na

1

Chromium (Cr)

26

0%

0.0001

0.03

0.05

1

Copper (Cu)

1053

1%

bd

1.78

2

1

Fluorine (F)

5640

19%

bd

15

1.5

2

Iron (Fe)

5576

5%

bd

148

0.3d

na

Mercury (Hg)

1

100%

0.018

0.018

0.001

0.002

Manganese (Mn)

5634

3%

bd

19.24

0.1d

na

Molybdenum (Mo)

33

15%

0.001

0.029

0.05

na

Nickel (Ni)

24

4%

0.001

0.032

0.02

1

Nitrate (NO3)

5576

1%

0.1

505

50

na

Lead (Pb)

2

50%

0.001

0.042

0.01

0.1

Selenium (Se)

2

50%

0.004

0.02

0.01

0.02

Uranium (U)

12

58%

0.001

0.019

0.017

0.02

Zinc (Zn)

1107

1%

bd

7.19

3d

2

Data: Bioregional Assessment Programme (Dataset 4)

aTable 3.4.1 in Australian Drinking Water Guidelines

bTable 4.3.2 in National Water Quality Management Strategy

cbd = Below detection limit

dAesthetic water quality trigger (not health related)

’na means ‘data not available’

Other water quality concerns

Trace elements with a significant fraction of samples in exceedance of the guidelines include arsenic, fluorine and boron (Table 15, column 2). Trace elements with a small number of samples in exceedance of the guidelines include mercury, cobalt, molybdenum and selenium. However, the number of analyses for these elements is too low to allow any informed statement about potential hazards they may pose.

1.5.2.2.4 Gaps

There are few samples available for many of the hydrogeologic units, in particular the Betts Creek beds and the Clematis-Warang Sandstone. This makes assessing the spatial distribution of water quality difficult, and requires assumptions about water quality over large areas with few control points.

The quality of the hydrochemistry data available for this assessment is difficult to determine, as analytical uncertainties are not reported in the dataset. The dataset includes chemical analyses of differing ages, sometimes decades apart, which will have differing levels of accuracy and precision. Additionally, stratigraphic data are not available for many bores in the dataset. Screened intervals are unknown for some bores, and others were not assigned stratigraphic units in the database. Assigning these bores to stratigraphic units based on depth and local stratigraphic information introduces a considerable amount of uncertainty into the dataset. Useful further work could include cross checking the stratigraphic position assigned to bores with limited stratigraphic information.

A number of potentially harmful trace elements have been omitted from consideration due to scarcity or absence of data. In general, suites of trace element analyses are only available from in the vicinity of coal resource development proposals. Some elements have data available for only one or two hydrogeologic units, while others have no data available at all. Trace elements for which there was only limited data are As, Co, Cd, Cr, Pb, Hg, Ni, U, Se and Mo. Trace elements for which there are no data are Ba, Be, Li, Rn, Sb and V.

Where analyses have been performed several elements have concentrations above ADWG or NWQMS triggers, but the current dataset is too sparse to make any informed statement about trigger value exceedances of these elements. It is possible that hazards will go unidentified due to data scarcity. Further work defining the range and distribution of trace element concentrations in the subregion is required to fully understand the potential hazards they pose.

The Queensland Department of Environment and Heritage Protection is establishing environmental values and water quality objectives under the Environmental Protection (Water) Policy 2009 for all Galilee subregion surface and groundwaters, including the Burdekin river basin (including the Belyando, Suttor, Cape and Bowen sub-basins), the Flinders river basin and Thomson and Barcoo rivers sub-basins during 2015 and 2016 (J Fewling (EHP), 2015, pers. comm.).

Last updated:
10 December 2018