We collected 38 groundwater and two surface water samples in the semi-arid Lake Woods region of the Northern Territory to better understand the hydrogeochemistry of this system, which straddles the Wiso, Tennant Creek and Georgina geological regions. Lake Woods is presently a losing waterbody feeding the underlying groundwater system. The main aquifers comprise mainly carbonate (limestone and dolostone), siliciclastic (sandstone and siltstone) and evaporitic units. The water composition was determined in terms of bulk properties (pH, electrical conductivity, temperature, dissolved oxygen, redox potential), 40 major, minor and trace elements as well as six isotopes (δ18Owater, δ2Hwater, δ13CDIC, δ34SSO4=, δ18OSO4=, 87Sr/86Sr). The groundwater is recharged through infiltration in the catchment from monsoonal rainfall (annual average rainfall ~600 mm) and runoff. It evolves geochemically mainly through evapotranspiration and water–mineral interaction (dissolution of carbonates, silicates, and to a lesser extent sulfates). The two surface waters (one from the main creek feeding the lake, the other from the lake itself) are extraordinarily enriched in 18O and 2H isotopes (δ18O of +10.9 and +16.4 ‰ VSMOW, and δ2H of +41 and +93 ‰ VSMOW, respectively), which is interpreted to reflect evaporation during the dry season (annual average evaporation ~3000 mm) under low humidity conditions (annual average relative humidity ~40 %). This interpretation is supported by modelling results. The potassium (K) relative enrichment (K/Cl mass ratio over 50 times that of sea water) is similar to that observed in salt-lake systems worldwide that are prospective for potash resources. Potassium enrichment is believed to derive partly from dust during atmospheric transport/deposition, but mostly from weathering of K-silicates in the aquifer materials (and possibly underlying formations). Further studies of Australian salt-lake systems are required to reach evidence-based conclusions on their mineral potential for potash, lithium, boron and other low-temperature mineral system commodities such as uranium. <b>Citation:</b> P. de Caritat, E. N. Bastrakov, S. Jaireth, P. M. English, J. D. A. Clarke, T. P. Mernagh, A. S. Wygralak, H. E. Dulfer & J. Trafford (2019) Groundwater geochemistry, hydrogeology and potash mineral potential of the Lake Woods region, Northern Territory, Australia, <i>Australian Journal of Earth Sciences</i>, 66:3, 411-430, DOI: 10.1080/08120099.2018.1543208

Freshwater coastal aquifers provide an important resource for irrigated agriculture, human consumption and the natural environment. Approximately 18 million people live within 50 km of the coast in Australia, and many coastal communities are reliant on groundwater. These coastal aquifers are vulnerable to seawater intrusion (SWI) - the landward encroachment of seawater - due to their close proximity to the ocean. To assess the threat of SWI in Australia, a comprehensive literature review was undertaken with input from state/territory agencies. The literature review, in combination with contributions from stakeholders, identified sites within each of the states and the Northern Territory where SWI had been reported or where it was considered to be a serious threat. International Association of Hydrogeologists 2013 Congress poster

The Clarence-Moreton and the Surat basins in Queensland and northern New South Wales contain the coal-bearing sedimentary sequences of the Jurassic Walloon Coal Measures, composed of up to approximately 600 m of mudstone, siltstone, sandstone and coal. In recent years, the intensification of exploration for coal seam gas (CSG) resources within both basins has led to concerns that the depressurisation associated with future resource development may cause adverse impacts on water resources in adjacent aquifers. In order to identify the most suitable tracers to study groundwater recharge and flow patterns within the Walloon Coal Measures and their degree of connectivity with over- or underlying formations, samples were collected from the Walloon Coal Measures and adjacent aquifers in the northern Clarence-Moreton Basin and eastern Surat Basin, and analysed for a wide range of hydrochemical and isotopic parameters. Parameters that were analysed include major ion chemistry, -13C-DIC, -18O, 87Sr/86Sr, Rare Earth Elements (REE), 14C, -2H and -13C of CH4 as well as concentrations of dissolved gases (including methane). Dissolved methane concentrations range from below the reporting limit (10 µg/L) to approximately 50 mg/L in groundwaters of the Walloon Coal Measures. However, the high degree of spatial variability of methane concentrations highlights the general complexity of recharge and groundwater flow processes, especially in the Laidley Sub-Basin of the Clarence-Moreton Basin, where numerous volcanic cones penetrate the Walloon Coal Measures and may form pathways for preferential recharge to the Walloon Coal Measures. Interestingly, dissolved methane was also measured in other sedimentary bedrock units and in alluvial aquifers in areas where no previous CSG exploration or development has occurred, highlighting the natural presence of methane in different aquifers. Radiocarbon ages of Walloon Coal Measure groundwaters are also highly variable, ranging from approximately 2000 yrs BP to >40000 yrs BP. While groundwaters sampled in close proximity to the east and west of the Great Dividing Range are mostly young, suggesting that recharge to the Walloon Coal Measures through the basalts of the Great Dividing Range occurs here, there are otherwise no clearly discernable spatial patterns and no strong correlations with depth or distance along inferred flow paths in the Clarence-Moreton Basin. In contrast to this strong spatial variability of methane concentrations and groundwater ages, REE and 87Sr/86Sr isotope ratios of Walloon Coal Measures groundwaters appear to be very uniform and clearly distinct from groundwaters contained in other bedrock units. This difference is attributed to the different source material of the Walloon Coal Measures (mostly basalts in comparison to other bedrock units which are mostly composed of mineralogical more variable Paleozoic basement rocks of the New England Orogen). This study suggests that REE and 87Sr/86Sr ratios may be a suitable tracer to study hydraulic connectivity of the Walloon Coal Measures with over- or underlying aquifers. In addition, this study also highlights the need to conduct detailed water chemistry and isotope baseline studies prior to the development of coal seam gas resources in order to differentiate between natural background values of methane and potential impacts of coal seam gas development.

The Great Artesian Basin Water Resource Assessment involves a basin-scale investigation of water resources to fill knowledge gaps about the status of water resources in the basin and the potential impacts of climate change and resource development. This report addresses findings in the Carpentaria region. Citation: Smerdon BD, Welsh WD and Ransley TR (eds) (2012) Water resource assessment for the Carpentaria region. A report to the Australian Government from the CSIRO Great Artesian Basin Water Resource Assessment. CSIRO Water for a Healthy Country Flagship, Australia.

The Great Artesian Basin Water Resource Assessment involves a basin-scale investigation of water resources to fill knowledge gaps about the status of water resources in the basin and the potential impacts of climate change and resource development. This report addresses findings in the Western Eromanga region. Citation: Smerdon BD, Welsh WD and Ransley TR (eds) (2012) Water resource assessment for the Western Eromanga region. A report to the Australian Government from the CSIRO Great Artesian Basin Water Resource Assessment. CSIRO Water for a Healthy Country Flagship, Australia

Modelled groundwater levels from 2010 to 2070 used to estimate the impact of climate change and future groundwater resource development on groundwater levels in the GAB. The modelling considered different scenarios of climate and groundwater development: Scenario A (historical climate and current development); Scenario C (future climate and current development) and Scenario D (future climate and future development). The future climate scenarios included the wet extreme (wet), the median (mid) and the dry extreme (dry). The raster grids "Cdry.grd"", "Cmid.grd" and "Cwet.grd" show predicted hydraulic head for the year 2070 based on projections of future climate and the continuation of current rates of groundwater extraction The files "Cdry-Base.grd", "Cmid-Base.grd" and ""Cwet-Base.grd" represent predicted differences between the hydraulic heads produced by Scenario C at 2070, and the modelled spatial distributions of hydraulic head for the year 2010 (Base scenario). The files "Cdry-A.grd", "Cmid-A.grd" and "Cwet-A.grd" represent predicted differences between hydraulic heads for 2070 produced by Scenario C and the current climate and development scenario (Scenario A). 'No data' value is 1e30 Cell size is 5000m x 5000m This data and metadata were produced by CSIRO for the Great Artesian Basin Water Resource Assessment. For more information, please refer to Welsh WD, Moore CR, Turnadge CJ, Smith AJ and Barr TM (2012), "Modelling of climate and groundwater development. A technical report to the Australian Government from the CSIRO Great Artesian Basin Water Resource Assessment ". CSIRO Water for a Healthy Country Flagship, Australia. Projection is Albers equal area conic, with central meridian 143 degrees longitude, standard parallels at -21 and -29 degrees latitude and latitude of projection's origin at -25.

Modelled groundwater levels from 2010 to 2070 used to estimate the impact of climate change and future groundwater resource development on groundwater levels in the GAB. The modelling considered different scenarios of climate and groundwater development: Scenario A (historical climate and current development); Scenario C (future climate and current development) and Scenario D (future climate and future development). The future climate scenarios included the wet extreme (wet), the median (mid) and the dry extreme (dry). The raster grids "Ddry.grd", "Dmid.grd" and "Dwet.grd" show predicted hydraulic head for the year 2070 based on projections of future climate and future development. The grids "Ddry-Base.grd", "Dmid-Base.grd" and "Dwet-Base.grd" represent predicted differences between the hydraulic heads produced by Scenario D at 2070, and the modelled spatial distributions of hydraulic head for the year 2010 (Base scenario). The grid "Dmid-Cmid.grd" represents the difference between the 2070 spatial distributions of hydraulic head that were produced by Scenario D (mid) and Scenario C (mid) 'No data' value is 1e30 Cell size is 5000m x 5000m This data and metadata were produced by CSIRO for the Great Artesian Basin Water Resource Assessment. For more information, please refer to Welsh WD, Moore CR, Turnadge CJ, Smith AJ and Barr TM (2012) "Modelling of climate and groundwater development. A technical report to the Australian Government from the CSIRO Great Artesian Basin Water Resource Assessment ". CSIRO Water for a Healthy Country Flagship, Australia. Projection is Albers equal area conic, with central meridian 143 degrees longitude, standard parallels at -21 and -29 degrees latitude and latitude of projection's origin at -25.

Layer 07 Base of Hutton Sandstone surface Surface produced for the Great Artesian Water Resource Assessment (GABWRA) by Geoscience Australia (http://www.ga.gov.au). This surface was created for 3D visualisation of the Base of Hutton Sandstone. The surface is available in the following formats 1. GOCAD surface (.ts) 2. ESRI grid 3. ASCII grid (.grd) Use limitations: 1. GOCAD surface requires program capable of reading GOCAD *.ts (triangulated surface) files 2. ASCII grid data requires re-interpolation by end-user resulting in minor differences to accompanying GOCAD *.ts surface This layer is part of a set comprised of: Layer 01 3-second Digital Elevation Model surface (catalogue #75990) Layer 02 Base of Cenozoic surface (catalogue #75991) Layer 03 Base of Mackunda Formation and equivalents surface (catalogue #76021) Layer 04 Base of Rolling Downs Group surface (catalogue #76022) Layer 05 Base of Hooray Sandstone and equivalents surface (catalogue #76023) Layer 06 Base of Injune Creek Group surface (catalogue #76024) Layer 07 Base of Hutton Sandstone surface (catalogue #76025) Layer 05-07 Base of Algebuckina Sandstone surface (catalogue #76952) Layer 08A Base of Evergreen and Marburg formations (catalogue #76026) Layer 08B Base of Poolowanna Formation (catalogue #76953) Layer 09 Base of Precipice Sandstone and equivalents surface (catalogue #76027) Layer 10 Base of Jurassic-Cretaceous sequence surface (catalogue #76028) This dataset and associated metadata can be obtained from www.ga.gov.au, using catalogue number 76025.

Layer 08A Base of Evergreen and Marburg formations Surface produced for the Great Artesian Water Resource Assessment (GABWRA) by Geoscience Australia (http://www.ga.gov.au). This surface was created for 3D visualisation of the Base of Poolowanna Formation. The surface is available in the following formats 1. GOCAD surface (.ts) 2. ESRI grid 3. ASCII grid (.grd) Use limitations: 1. GOCAD surface requires program capable of reading GOCAD *.ts (triangulated surface) files 2. ASCII grid data requires re-interpolation by end-user resulting in minor differences to accompanying GOCAD *.ts surface. This layer is part of a set comprised of: Layer 01 3-second Digital Elevation Model surface (catalogue #75990) Layer 02 Base of Cenozoic surface (catalogue #75991) Layer 03 Base of Mackunda Formation and equivalents surface (catalogue #76021) Layer 04 Base of Rolling Downs Group surface (catalogue #76022) Layer 05 Base of Hooray Sandstone and equivalents surface (catalogue #76023) Layer 06 Base of Injune Creek Group surface (catalogue #76024) Layer 07 Base of Hutton Sandstone surface (catalogue #76025) Layer 05-07 Base of Algebuckina Sandstone surface (catalogue #76952) Layer 08A Base of Evergreen and Marburg formations (catalogue #76026) Layer 08B Base of Poolowanna Formation (catalogue #76953) Layer 09 Base of Precipice Sandstone and equivalents surface (catalogue #76027) Layer 10 Base of Jurassic-Cretaceous sequence surface (catalogue #76028) This dataset and associated metadata can be obtained from www.ga.gov.au, using catalogue number 76953.

Layer 08B Base of Poolowanna Formation Surface produced for the Great Artesian Water Resource Assessment (GABWRA) by Geoscience Australia (http://www.ga.gov.au). This surface was created for 3D visualisation of the Base of Poolowanna Formation . The surface is available in the following formats 1. GOCAD surface (.ts) 2. ESRI grid 3. ASCII grid (.grd) Use limitations: 1. GOCAD surface requires program capable of reading GOCAD *.ts (triangulated surface) files 2. ASCII grid data requires re-interpolation by end-user resulting in minor differences to accompanying GOCAD *.ts surface This layer is part of a set comprised of: Layer 01 3-second Digital Elevation Model surface (catalogue #75990) Layer 02 Base of Cenozoic surface (catalogue #75991) Layer 03 Base of Mackunda Formation and equivalents surface (catalogue #76021) Layer 04 Base of Rolling Downs Group surface (catalogue #76022) Layer 05 Base of Hooray Sandstone and equivalents surface (catalogue #76023) Layer 06 Base of Injune Creek Group surface (catalogue #76024) Layer 07 Base of Hutton Sandstone surface (catalogue #76025) Layer 05-07 Base of Algebuckina Sandstone surface (catalogue #76952) Layer 08A Base of Evergreen and Marburg formations (catalogue #76026) Layer 08B Base of Poolowanna Formation (catalogue #76953) Layer 09 Base of Precipice Sandstone and equivalents surface (catalogue #76027) Layer 10 Base of Jurassic-Cretaceous sequence surface (catalogue #76028) This dataset and associated metadata can be obtained from www.ga.gov.au, using catalogue number 76953.