Hydrogeology of the Beetaloo GBA region Technical appendix for the Geological and Bioregional Assessment: Stage 2 2020 A scientific collaboration between the Department of Agriculture, Water and the Environment, Bureau of Meteorology, CSIRO and Geoscience Australia The Geological and Bioregional Assessment Program The Geological and Bioregional Assessment Program will provide independent scientific advice on the potential impacts from development of selected unconventional hydrocarbon plays on water and the environment. The geological and environmental data and tools produced by the Program will assist governments, industry, landowners and the community to help inform decision making and enhance the coordinated management of potential impacts. The Program is funded by the Australian Government Department of the Environment and Energy. The Department of the Environment and Energy, Bureau of Meteorology, CSIRO and Geoscience Australia are collaborating to undertake geological and bioregional assessments. For more information, visit http://www.bioregionalassessments.gov.au. Department of the Environment and Energy The Department designs and implements Australian Government policy and programs to protect and conserve the environment, water and heritage, promote climate action, and provide adequate, reliable and affordable energy. For more information visit http://www.environment.gov.au. Bureau of Meteorology The Bureau of Meteorology is Australia’s national weather, climate and water agency. Under the Water Act 2007, the Bureau is responsible for compiling and disseminating Australia's water information. The Bureau is committed to increasing access to water information to support informed decision making about the management of water resources. For more information, visit http://www.bom.gov.au/water/. CSIRO Australia is founding its future on science and innovation. Its national science agency, CSIRO, is a powerhouse of ideas, technologies and skills for building prosperity, growth, health and sustainability. It serves governments, industries, business and communities across the nation. For more information, visit http://www.csiro.au. Geoscience Australia Geoscience Australia is Australia’s national geoscience agency and exists to apply geoscience to Australia’s most important challenges. Geoscience Australia provides geoscientific advice and information to the Australian Government to support current priorities. These include contributing to responsible resource development; cleaner and low emission energy technologies; community safety; and improving marine planning and protection. The outcome of Geoscience Australia’s work is an enhanced potential for the Australian community to obtain economic, social and environmental benefits through the application of first-class research and information. For more information, visit http://www.ga.gov.au. ISBN-PDF 978-1-76003-277-7 Citation Evans TJ, Radke BM, Martinez J, Buchanan S, Cook SB, Raiber M, Ransley TR, Lai ÉCS, Skeers N, Woods M, Evenden C, Cassel R and Dunn B (2020) Hydrogeology of the Beetaloo GBA region. Technical appendix for the Geological and Bioregional Assessment: Stage 2. Department of the Environment and Energy, Bureau of Meteorology, CSIRO and Geoscience Australia, Australia. Authorship is listed in relative order of contribution. On 1 February 2020 the Department of the Environment and Energy and the Department of Agriculture merged to form the Department of Agriculture, Water and the Environment. Work for this document was carried out under the then Department of the Environment and Energy. Therefore, references to both departments are retained in this report. Copyright © Commonwealth of Australia 2020 With the exception of the Commonwealth Coat of Arms and where otherwise noted, all material in this publication is provided under a Creative Commons Attribution 4.0 International Licence https://creativecommons.org/licenses/by/4.0/. The Geological and Bioregional Assessment Program requests attribution as ‘© Commonwealth of Australia (Geological and Bioregional Assessment Program http://www.bioregionalassessments.gov.au)’. Disclaimer The information contained in this report is based on the best available information at the time of publication. The reader is advised that such information may be incomplete or unable to be used in any specific situation. Therefore, decisions should not be made based solely on this information or without seeking prior expert professional, scientific and technical advice. The Geological and Bioregional Assessment Program is committed to providing web accessible content wherever possible. If you are having difficulties with accessing this document please contact [email protected]. Cover photograph Mataranka Thermal Pools, Beetaloo GBA extended region, October 2018. Credit: Alf Larcher (CSIRO) Element: GBA-BEE-2-381 v20210630 Executive summary This investigation reviews the existing datasets and literature to develop a regional hydrogeological conceptualisation of the Beetaloo Geological and Bioregional Assessment region. The region is located approximately 500 km south-east of Darwin, in the Northern Territory, Australia, and covers approximately 28,000 km2. The hydrogeology is characterised by a complex series of stacked sedimentary basins that include the Beetaloo Sub-basin (Roper Group); the Georgina, Wiso, and Daly basins; and the Carpentaria Basin. Within these basins, four primary groundwater and aquitard sub-systems have been identified. A brief summary of these is provided below. Mesoproterozoic Roper Group: The group is host to the main hydrocarbon plays of the Velkerri and Kyalla formations. While the Roper Group typically exhibits aquitard properties, the Moroak Sandstone can locally act as a fractured rock aquifer near structures. It has produced groundwater inflows to petroleum wells during drilling. Due to depth and hypersaline conditions, the Moroak Sandstone is not utilised as a groundwater resource within the Beetaloo GBA region. Outside the Beetaloo GBA region, however, where these rocks occur near surface, the Moroak and other sandstones in the Roper Group are utilised and may also be a source aquifer for some springs. Neoproterozoic units: Overlying the Roper Group are the Jamison sandstone aquifer, Hayfield mudstone and Kiana Group. Outside the region the Jamison sandstone is utilised as a groundwater source. While this unit is being considered as an option for water supply for future petroleum drilling operations within the region, a couple of water quality samples suggest at least parts of it could be highly saline. The overlying Hayfield mudstone is a regional aquitard found across the majority of the Beetaloo GBA region, except for small regions in the extreme north and south. The Kiana Group consists of Bukalara Sandstone and Cox Formation. The Bukalara Sandstone has a discontinuous distribution, within and adjacent to, the Beetaloo GBA region. This unit is a good local aquifer where it outcrops to the north of the region. The Bukalara Sandstone is being considered as an option for future water supplies. Limited information from petroleum wells drilled within the Beetaloo GBA region suggests that parts of the Bukalara Sandstone have potentially relatively good hydraulic conductivity and porosity. There is no information on water quality. Antrim Plateau Volcanics: While considered to be a regional aquitard across much of the Beetaloo GBA region, it is used as a local aquifer where groundwater supply from the Cambrian Limestone Aquifer is not sufficient. Cambrian Limestone Aquifer: The Cambrian Limestone Aquifer (CLA) is the most important aquifer in the Beetaloo GBA region, due to its relatively shallow nature, high yields and good water quality. The CLA stratigraphy is complex, karstic in nature and includes a number of variably hydraulically connected sequences: The Cambrian Antrim Plateau Volcanics underlies the CLA. Hydrogeology of the Beetaloo GBA region | i There are two regional groundwater flow systems recognised in the CLA: groundwater flow from the Wiso Basin into the Daly Basin, and groundwater flow from the Georgina Basin into the Daly Basin. Inferred regional groundwater flow for both systems are north-westward, across the Beetaloo GBA region, into the Daly Basin and discharges at spring complexes such as Mataranka and Flora River Springs located outside the GBA region. Groundwater flow on a more local scale is, however, poorly defined. Within the CLA, the velocity of groundwater flow can be highly variable and is in part dependent on the degree of connectivity and size of karst porosity. Cretaceous Carpentaria Basin and Cenozoic sediments: These are generally unsaturated and provide only limited quantities of low to moderately saline groundwater. Within the Beetaloo GBA region, local perched aquifers in the Cenozoic could potentially be used as a water source by vegetation. Hydraulic connectivity: Hydraulic connectivity and potential impact propagation between the prospective Roper Group units and the upper aquifers are expected to be limited by variably extensive and thick aquitards, particularly the Hayfield mudstone and Antrim Plateau Volcanics. The degree of inter-aquifer connectivity is not well characterised. The thickness of Carpentaria Basin sedimentary rocks and distribution of near-surface karst have a bearing on degree of leakage/recharge that can reach the underlying CLA. This has implications for hazards such as spills, because recharge/leakage is impeded where overlying