Hydrogeology and groundwater systems of the Isa 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 shale and tight gas projects on 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. 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ISBN-PDF 987-1-921069-30-7 Citation Buchanan S, Dixon-Jain P, Martinez J, Raiber M, Kumar PR, Woods M, Arnold D, Dehelean A and Skeers N (2020) Hydrogeology and groundwater systems of the Isa 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. 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 Australia Licence https://creativecommons.org/licenses/by/4.0/. The Bioregional Assessment Programme requests attribution as ‘© Commonwealth of Australia (Bioregional Assessment Programme 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 The Burketown Bore, drilled in 1897 by the Queensland Government, is a naturally flowing bore that taps the artesian Gilbert River Formation aquifer at a depth of about 700 m below surface. Groundwater within this aquifer naturally contains a variety of dissolved chemical compounds that have deposited around the bore as the hot water (around 68 °C) has evaporated over the years, leading to the formation of a distinctive multi-coloured mound. Credit: Steven Lewis, Geoscience Australia, July 2018 Element: GBA-ISA-2-264 v20200228 Executive summary This technical appendix focuses on the hydrogeology and groundwater systems of the Isa GBA region in north-west Queensland. This region includes part of the Isa Superbasin, a Paleoproterozoic to earliest Mesoproterozoic superbasin of the North Australian Craton. The Isa GBA region is in the Northern Lawn Hill Platform, an area where petroleum exploration (for both conventional and unconventional resources) has previously occurred. The Isa GBA region is host to two groundwater systems that are potentially connected: 1. groundwater associated with the Proterozoic rock units of the Isa Superbasin and South Nicholson Basin – typically the deeper groundwater system in the region 2. groundwater associated with the overlying Jurassic to Cretaceous Carpentaria Basin (part of the Great Artesian Basin or GAB) and Karumba Basin. The supersequences of the Isa Superbasin and South Nicholson Basin rocks extend from outcrop in the west of the Isa GBA region and dip southwards to depths of over 9 km. These older basin sequences are overlain by younger sediments of the Mesozoic Carpentaria and Cenozoic Karumba basins in central and eastern parts of the region. The Proterozoic units of the Isa Superbasin and South Nicholson Basin are generally highly lithified fine-grained rocks, typically with aquitard properties, and include the prospective shale gas plays of the Lawn and River supersequences. Groundwater exploration of these units has been limited; however, some of the carbonate-dominated lithofacies, particularly the Lady Loretta Formation (Loretta Supersequence) and to a lesser degree the Paradise Creek Formation and Esperanza Formation, exhibit aquifer properties, potentially under artesian pressure. The Carpentaria Basin (GAB) overlies the Proterozoic units and covers most of the assessment area. The basin consists of a variably confined groundwater system comprising a multi- layered complex of aquifers of variable character within predominantly continental sandstones. Within the assessment area are two regionally recognised aquifers of the GAB: 1. The Gilbert River Formation and underlying basal Jurassic to Cretaceous aquifer system of the Eulo Queen Group 2. The Late Cretaceous Normanton Formation aquifer. These two groundwater systems are separated by the Rolling Downs Group aquitard, which forms a substantial low-permeability zone that is up to about 500 m thick in eastern parts of the region. Overlying the Carpentaria Basin is the Cenozoic Karumba Basin, a thin (typically less than 50 m thick in the region) sedimentary basin hosting a series of partial aquifers and leaky aquitards. The aquifers of the Carpentaria and Karumba basins are more widely utilised than the Proterozoic groundwater systems in the region. Of the 190 registered groundwater bores within the assessment area for this study, 152 are in the Carpentaria and Karumba basins, providing the shallowest and most economically important groundwater resources. The Hydrogeology and groundwater systems of the Isa GBA region | i remaining 38 bores (all in the west of the region) access groundwater from the Proterozoic rock units of the Isa Superbasin and South Nicholson Basin. The regional watertable aquifer, which lies in the Karumba Basin across most of the region, flows to the north-east towards the Gulf of Carpentaria. Groundwater in the confined Gilbert River Formation aquifer is typically under artesian pressure and the direction of groundwater flow is uncertain. The groundwater flow direction in the Proterozoic units has not been established due to the lack of available water level data and the potential influence of major fault structures in compartmentalising groundwater flow systems. Groundwater within all of the aquifers in the region is of low to moderate salinity, with median total dissolved solid (TDS) concentrations typically of 600 to 1400 mg/L. The potential exists for intra-basin groundwater connectivity throughout the region, both within the Proterozoic units of the Isa Superbasin and South Nicholson Basin as well as the overlying Carpentaria and Karumba basins. In addition, five hydrological connectivity pathways that can potentially link shale gas reservoirs to overlying aquifers or near-surface environmental and economic