Nine existing datasets with useful hydrogeological information were analysed for the bioregional assessment of the Galilee subregion. Table 7 lists the datasets and identifies the information that was analysed.
Table 7 Data used for hydrogeological analysis of the Galilee subregion
|
Dataset title |
Source |
Information analysed |
|---|---|---|
|
Hydrochemistry analysis of the Galilee subregion |
Bioregional Assessment Programme (Dataset 1) |
Major ions, alkalinity, total dissolved solids (TDS), trace elements, sodium absorption ratio (SAR) |
|
QLD Department of Natural Resources and Mining Groundwater Database Extract 20142808 |
Queensland Department of Natural Resources and Mines (Dataset 2) |
Location, water level, standing water level, bore construction, hydrostratigraphy, water chemistry |
|
Queensland petroleum exploration data - QPED |
Geological Survey of Queensland, Department of Natural Resources and Mines (Dataset 3) |
Locations, stratigraphy, drill stem formation tests (DST) e.g. temperature, salinity |
|
QDEX Well Completion Reports (WCR) - Galilee v01 |
Queensland Department of Employment, Economic Development and Innovation (Dataset 4) |
Stratigraphy, drill stem formation tests (DST) e.g. pressure, temperature, salinity data, not included in QPED, from open file well completion reports |
|
Carmichael Coal Mine and Rail Project Environmental Impact Statement |
Queensland Government Department of State Development, Infrastructure and Planning (Dataset 5) |
Bore location, stratigraphy, water levels, hydraulic head (mAHD), well screen intervals, temperature and water chemistry |
|
China First Galilee Coal Project Environmental Impact Assessment |
Waratah Coal Pty Ltd (Dataset 6) |
Bore location, stratigraphy, water levels, hydraulic head (mAHD), well screen intervals, temperature and water chemistry |
|
Kevin's Corner Project Environmental Impact Statement |
Hancock Galilee Pty Ltd (Dataset 7) |
Bore location, stratigraphy, water levels, hydraulic head (mAHD), well screen intervals, temperature and water chemistry |
|
South Galilee Coal Project Environmental Impact Statement |
AMCI (Alpha) Pty Ltd (Dataset 8) |
Bore location, stratigraphy, water levels, hydraulic head (mAHD), well screen intervals, temperature and water chemistry |
|
QLD Dept. of Natural Resources and Mines, Groundwater Entitlements linked to bores and NGIS v4 28072014 |
Bioregional Assessment Programme (Dataset 9) |
Borehole stratigraphy |
The primary source for groundwater data is the Queensland Department of Natural Resources and Mines Groundwater Database (Dataset 2). It contains information on registered groundwater bores in the state of Queensland. The bore database has a number of tables which include data on: bore registration (location information), bore construction; stratigraphy, lithology, water levels, aquifer test data, water quality data, as well as other bore related information. Department of Natural Resources and Mines (DNRM, 2013) provides detail on groundwater database structure and content.
Other significant sources of groundwater data were environmental impact statements (EISs) (Dataset 5 to Dataset 8) for proposed coal resource developments in the Galilee subregion and formation tests undertaken in wells drilled for coal seam gas (CSG) and petroleum exploration (Dataset 3 and Dataset 4). EISs are a key source of information as they contain recent data pertaining to groundwater systems in and near proposed development areas. Formation tests are one of the few sources of information on pressures in the deeper groundwater flow systems.
2.1.3.1.1 Hydrostratigraphy
The Galilee subregion BA is focused on two stacked geological basins – the Eromanga Basin and the Galilee Basin – that in some places are overlain by Cenozoic sediments. While parts of the Drummond, Adavale and Belyando basins are in contact with the base of the Galilee Basin, these basins are isolated from the areas of coal resource development and are not considered further.
The Galilee subregion includes the following geological environments which generally represent individual (or in some cases connected) groundwater systems:
- Cenozoic aquifers
- Early Jurassic to Early Cretaceous layered aquifers and aquitards of the Eromanga Basin (Great Artesian Basin (GAB))
- Late Carboniferous, Permian to Late Triassic layered aquifers and aquitards of the Galilee Basin. The upper Permian coal measures and correlatives host the coal seams that are targeted for mining.
Previous hydrogeological investigations within the Galilee subregion have been mainly restricted to local scale investigations focused in and around areas of potential coal mining developments. As such, prior to this BA, the understanding of the regional hydrogeology of the Galilee Basin was limited.
For the purposes of this bioregional assessment, a number of analyses have been undertaken to better understand the current hydrogeological characteristics of the region, which, in turn, allows an enhanced conceptual understanding of the effects of potential coal mining developments modelled in BA companion products 2.6.1 (Karim et al., 2018b) and 2.6.2 (Peeters et al., 2018) for the Galilee subregion.
The analyses include the following:
The above analyses are aimed specifically at improving our understanding of: the hydrodynamics of the system – groundwater flow, chemical evolution, areas of possible inter-aquifer leakage and recharge and discharge processes; and the current water level trends prior to coal resource development.
The hydrostratigraphy of the Galilee subregion is summarised in Figure 34.
The hydrostratigraphic units to which samples were assigned are outlined in companion product 1.5 for the Galilee subregion (Evans et al., 2014), with the following amendments:
- The Wyandra-Hooray grouping is hereafter referred to as the Cadna-owie – Hooray aquifer because the majority of samples available are sourced from the Cadna-owie Formation or Hooray Sandstone.
- The Injune Creek Group includes the Westbourne Formation, Adori Sandstone and Birkhead Formation.
- The Clematis-Warang Sandstone is now referred to as the Clematis Group aquifer as outlined in Section 2.1.2 of this product.
- The Betts Creek beds are now referred to as the upper Permian coal measures.
These changes in title have not changed the hydrostratigraphic units that any samples were assigned to.
There is some variation between the geological units used for each type of analyses undertaken in the following sections. This is due to variability in the amount and spatial distribution of the available data for each individual geological unit. Hydrochemistry, water level mapping and aquifer pressure comparison analyses use hydrostratigraphic groupings for some units with similar hydrogeological characteristics. Whereas, the water level trend and recharge analyses are reported based on individual stratigraphic units. Descriptions of the units and groupings used are provided at the beginning of each respective section.
2.1.3.1.2 Hydrochemistry data and processing
Hydrochemistry data were obtained from the Queensland DNRM groundwater bore database. A subset of this dataset was extracted for the Galilee subregion. Few bores had a complete suite of analyses for hydrochemistry, and data quality was highly variable. In some instances insufficient information (e.g. a description of the aquifer tapped and/or casing and depth information) was available to confidently determine the source aquifer for particular analyses. In such cases these analyses were discarded and not used for the subsequent interpretation. The initial hydrochemical dataset comprised 5680 samples with information for:
- bore identification (RN) and location
- data source
- aquifer information for some bores, including formations intercepted by monitoring wells and screened intervals
- sample information (e.g. date sampled)
- field parameters (pH, electrical conductivity, temperature, dissolved oxygen, redox)
- total dissolved solids (TDS)
- alkalinity
- major ions
- selected trace elements.
2.1.3.1.2.1 Quality assurance / quality control analysis of data
Prior to analysis all hydrochemistry data were assessed for reliability by quality assurance/quality control (QA/QC) procedures. A data audit and verification were performed using various quality checking procedures including identification and verification of outliers.
The charge balance of major ions in each sample was used to assess the reliability of the data. In some cases, alkalinity was expressed as calcium carbonate which required conversion to alkalinity as bicarbonate to achieve ionic charge balance.
The charge balance of each sample was determined using the following equation:
|
|
(1) |
where Cat = the concentration of all cations in solution in milliequivalents per litre (meq/L), and An = the concentration of all anions in meq/L. Using milliequivalents accounts for the charge and molecular weight of each ion.
Theoretically the meq/L of anions in solution should be equal to the meq/L of cations, since natural solutions are electrically neutral. This means the deviation from zero in the charge balance calculation gives an indication of the potential error associated with the sample data. Given the age range and geographical extent of the groundwater data analysed by the BA programme, an ionic charge balance of 10% was deemed acceptable. Samples which exceeded this error threshold were discarded.
Measurements of field electrical conductivity (EC) data were limited, with many zero or missing values present. An initial investigation of the EC-TDS ratio of each sample within a particular hydrogeologic unit revealed a range of ratios from 0.2 to 12. To avoid the influence of outliers and obvious EC measurement errors, interpolation of TDS from the EC-TDS regression was only applied to the EC range between 0.50 and 0.90.
Further filtering of the data was required for some of the hydrochemical methods employed. This will be discussed in Section 2.1.3.2.1.
To interpret the hydrochemistry data it was necessary to assign each sample to a hydrogeologic unit. Data that passed the initial QA/QC procedures were checked against borehole construction and stratigraphic records to determine aquifer intercepts. Data were discarded in cases where there was no recorded screen interval or depth information that could be cross referenced with borehole stratigraphy, or where bores were screened in multiple aquifers. A total of 4624 samples which passed the initial QA/QC process had sufficient stratigraphic data to be assigned to a hydrogeologic unit.
2.1.3.1.3 Standing water level and hydraulic head
Standing water level (SWL) is a measurement of the depth below a reference point to the water level in a bore. SWL data were converted to hydraulic head (groundwater level above a reference point, usually the Australian Height Datum). Certain types of hydrogeological analyses require SWL to be compared between water bores. In such cases, hydraulic head is corrected to an equivalent fresh water hydraulic head. The correction requires the measurement reference point elevation to convert SWL to uncorrected hydraulic head. In turn, water salinity and temperature data are required to calculate equivalent fresh water hydraulic head.
Regional plots of water level depth are used to infer hydraulic processes such as potential groundwater flow direction and recharge processes.
To interpret SWL data, the hydrostratigraphic unit(s) in which the bore is screened must be determined. In some cases a bore may be drawing water from more than one hydrostratigraphic unit. Section 2.1.3.1.1 and Evans et al. (2014) details the stratigraphy and hydrostratigraphy for the Galilee subregion.
2.1.3.1.3.1 Datasets and processing
QLD Department of Natural Resources and Mining Groundwater Database (Dataset 2)
SWL data for groundwater bores are primarily stored in the ‘water levels’ table in Dataset 2. Some SWL data, mainly for artesian bores, are also available from the ‘pumping test and design’ table of Dataset 2. Many of these measurements are also duplicated in the water levels table. SWL and other relevant data for hydrogeological analysis were extracted from Dataset 2 and incorporated with data from other sources using the following steps:
- Using a GIS package, select bores located within the Galilee preliminary assessment extent (PAE) area. Based on the Registered Number (RN) from the filtered GIS dataset, extract and join data from the following tables contained in Dataset 2: registrations, aquifers, stratigraphy, construction, lithology, water analysis, field water quality and elevation.
- Check and assign elevation data that referenced the Australian Height Datum (AHD) and were derived from a survey or GPS elevation measurement. Where no elevation data were available in Dataset 2 (mostly private bores), the elevation was derived from the 1-second digital elevation model (DEM) (Geoscience Australia, Dataset 10).
- Determine screened intervals using the construction table in Dataset 2. In the construction table these intervals are designated in the material description column as either: open, perforated, screened or VWPZ (vibrating wire piezometer). Sometimes bores can have multiple ingress points for groundwater. In the BA dataset, the screen ‘From’ measurement represents uppermost interval and screen ‘To’ represents the base of the interval at which groundwater can enter a bore.
- Determine hydrostratigraphic unit sample intercept by cross checking screened interval with hydrostratigraphic interval interpretation. In Dataset 2, stratigraphic information is sourced from the aquifer and stratigraphy tables. Stratigraphic data from these sources can be missing, incomplete, or the stratigraphic interpretation may have changed since data were originally input. To infill data gaps, extra stratigraphic data were incorporated from a number of additional datasets including groundwater bore entitlements and licences (Bioregional Assessment Programme, Dataset 9) and Queensland Petroleum Exploration Data (Department of Employment, Economic Development and Innovation, Dataset 4). Stratigraphic data were queried for each bore and compared for consistency and completeness. A number of bores draw groundwater from multiple aquifers.
For bores with missing or incomplete screen interval data, the maximum recorded drilling depth was used as a proxy for the base of screened interval. However, it should be noted that in some cases using total depth as a proxy for base of screens may not be representative of the screened interval. For example in some cases a bore may be uncased below a certain depth and the open interval in the bore could be large and intersect multiple aquifers.
Queensland petroleum exploration data - QPED (Dataset 3) and QDEX Well Completion Reports (WCR) (Dataset 4)
Basic data from petroleum and CSG wells are archived in the Department of Employment, Economic Development and Innovation (Dataset 4).Open file well completion reports (WCR) can be downloaded as required from the Department of Employment, Economic Development and Innovation (Dataset 4), which is the Queensland Digital Exploration Reports system. Detailed results such as pressures, recorded by formation tests were obtained from the WCR and associated datasets.
Various types of formation testing are commonly undertaken in petroleum and CSG wells as part of petroleum resource assessments. Over discrete intervals these tests can be used to assess: the presence of hydrocarbons, determine reservoir properties (pressures, temperatures, flow rates), well performance, and obtain samples of reservoir fluids.
Formation test and other data, for use in bioregional assessments, were data-mined using the following steps:
- Identify which bores are located within the Galilee PAE area, using a GIS package.
- Record drilling datum and ground levels in mAHD.
- Where available, record detailed stratigraphy in the coal-bearing sequences, not already in the Queensland Petroleum Exploration Database (QPED) database.
- Formation test data: record test type, depth; formation tested; salinity (if available); pressure measurement units; inside and outside gauge pressures; gauge temperature, interpreted test results (if available) and any comments on test performance.
- Record water analysis data not already in QPED database.
Datasets 5 to 8 – environmental impact statements
Groundwater bore data were obtained from available company EISs and tabulated in spreadsheets. Data included bore location, stratigraphy, water levels, hydraulic head (mAHD), well screen intervals, temperature and chemistry. Stratigraphic data in most of the EIS are more detailed (mine scale stratigraphy) than those available in Queensland Department of Natural Resources and Mines (Dataset 2). This level of detail was required for the BA groundwater model (in companion product 2.6.2 for the Galilee subregion (Peeters et al., 2018)).
2.1.3.1.4 Corrected hydraulic head calculation
2.1.3.1.4.1 Corrected hydraulic head from Dataset 2 and Dataset 5 to Dataset 8
Where possible, hydraulic head was corrected to a fresh water equivalent hydraulic head. Water salinity and temperature data are required to calculate equivalent fresh water hydraulic head using the process described in Post et al. (2007). Many water level measurements could not be corrected due to an absence of corresponding temperature or salinity measurements.
To correct hydraulic head to an equivalent freshwater hydraulic head the following steps were undertaken:
- Data from Dataset 2, and Dataset 5 to Dataset 8 were combined.
- Water level records missing temperature readings: to fill in gaps, temperature data from non-flowing groundwater bores and all formation tests were plotted on a temperature versus depth plot. A linear regression line based on the data provided the formula to which an approximate temperature for a given depth could be calculated.
- Water level records missing salinity readings: to fill data gaps, from the compiled data, the mean EC for a given formation was used as a proxy for salinity.
- Salinity: EC measurements (including calculated EC) were converted to TDS in mg/L in order to calculate corrected hydraulic head. Further discussion on the factors used for conversion from EC to TDS can be found in Section 2.1.3.2.
- Equivalent freshwater hydraulic head was calculated using methods outlined in Post et al. (2007).
2.1.3.1.4.2 Corrected hydraulic head from formation pressure test data
Additional steps are required to obtain a freshwater equivalent hydraulic head from formation test pressure measurements. Firstly, quality assurance protocols were applied to the available data, before pressure measurements were converted to freshwater equivalent hydraulic head.
The QA process and corrected head calculation involved:
- quality assurance checks such as: Was the formation test classed as successful by the operator and all test gauges operational? Were all data present? Was final shut-in pressure less than final hydrostatic pressure? Did the pressure build-up phase of the test stabilise around a final value? Further detail on formation test quality control can be found in Hortle et al. (2013)
- for successful tests, ensuring that final shut-in pressures reference pounds per square inch gauge (PSIG) and not pounds per square inch absolute (PSIA). PSIG was chosen as the reference because there is no information on whether SWL readings were corrected for atmospheric pressure changes at the time the SWL measurement was made
- converting final shut-in pressure (PSIG) to fresh water equivalent hydraulic head as per steps 4 and 5 in the previous section.
Most formation tests had temperature data, although they lacked salinity data. Where no salinity data were available, water salinity was assumed to be the mean aquifer salinity.
Water level maps of hydraulic head are presented in Section 2.1.3.2.2. In areas where groundwater level data were unavailable, formation test data obtained from Dataset 3 and Dataset 4 were used to aid interpretation.
With the exception of Cenozoic aquifer water levels maps, all potentiometric surfaces are corrected to a common datum of 25 °C and equivalent fresh water head.
