Technical Report for the National Collaboration Framework Regional Hydrogeology Project
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Record 2015/14 | GeoCat 78882 Regional Hydrogeological Characterisation of the Maryborough Basin, Queensland Technical report for the National Collaboration Framework Regional Hydrogeology Project Marshall, S. K., Fontaine, K., Kilgour, P. L. and Lewis, S. J. APPLYING GEOSCIENCE TO AUSTRALIA’S MOST IMPORTANT CHALLENGES www.ga.gov.au Regional Hydrogeological Characterisation of the Maryborough Basin, Queensland Technical report for the National Collaboration Framework Regional Hydrogeology Project GEOSCIENCE AUSTRALIA RECORD 2015/14 Marshall, S. K., Fontaine, K., Kilgour, P. L. and Lewis, S. J. Department of Industry and Science Minister for Industry and Science: The Hon Ian Macfarlane MP Parliamentary Secretary: The Hon Karen Andrews MP Secretary: Ms Glenys Beauchamp PSM Geoscience Australia Chief Executive Officer: Dr Chris Pigram This paper is published with the permission of the CEO, Geoscience Australia © Commonwealth of Australia (Geoscience Australia) 2015 With the exception of the Commonwealth Coat of Arms and where otherwise noted, this product is provided under a Creative Commons Attribution 4.0 International Licence. (http://creativecommons.org/licenses/by/4.0/legalcode) Geoscience Australia has tried to make the information in this product as accurate as possible. However, it does not guarantee that the information is totally accurate or complete. Therefore, you should not solely rely on this information when making a commercial decision. Geoscience Australia is committed to providing web accessible content wherever possible. If you are having difficulties with accessing this document please email [email protected]. ISSN 2201-702X (PDF) ISBN 978-1-925124-73-6 (PDF) GeoCat 78882 Bibliographic reference: Marshall, S. K., Fontaine, K., Kilgour, P. L. & Lewis, S. J. 2015. Regional Hydrogeological Characterisation of the Maryborough Basin, Queensland: technical report for the National Collaboration Framework Regional Hydrogeology Project. Record 2015/14. Geoscience Australia, Canberra. http://dx.doi.org/10.11636/Record.2015.014 Acknowledgements: This work was funded by the Department of the Environment – Office of Water Science. The authors would like to acknowledge staff from the Office of Water Science at the Department of the Environment for their assistance with this National Collaboration Framework Project on the Regional Hydrogeological Characterisation of the Maryborough Basin. Malcolm Cox from Queensland University of Technology provided useful resources for the hydrogeological characterisation and Gerard Stewart, Joseph Bell and Luke Caruana from Geoscience Australia helped with data organisation and GIS support. Geoscience Australia’s Products and Promotions team, in particular, Daniel McIlroy, Veronika Galinec and Daniel Rawson, generated many of the figures and helped in the final design of the report. Many staff from the Geoscience Australia Groundwater Group also provided assistance to the authors, and John Magee, Pauline English, Gabrielle Yates, Martin Smith and Jon Clarke are especially acknowledged for their discussions and advice regarding the integrity and relevance of the interpretations within the report. We also acknowledge the helpful comments from an independent anonymous reviewer, which helped to significantly improve the final version of the report. Summary The Maryborough Basin is a geological basin in South East Queensland, situated on the coastline approximately 250 km north of Brisbane. It covers an area of 24,600 km2, of which about 37% occurs onshore. There are several major population centres within the basin, including Bundaberg, Hervey Bay and Maryborough. The geological basin is infilled by up to 9 km of Mesozoic sedimentary rocks, with two stratigraphic units containing variably thick seams of black coal (individual seams are generally less than 1 m thick). These formations are the Cretaceous Burrum Coal Measures and the deeper Jurassic Tiaro Coal Measures. The Mesozoic rocks are capped across most of the basin by relatively thin Cenozoic sediments comprising sands, silts and gravels. The Mesozoic rock strata in the basin are commonly folded and faulted, although the intensity and style of geological structures varies across the basin. The Maryborough Basin supports major agricultural industry (especially sugar cane production) and contains environmentally significant areas such as the World Heritage-listed Fraser Island. Both agriculture and the environment rely strongly on groundwater systems within the basin. Although no coal mining or coal seam gas (CSG) extraction presently occurs, several historic coal workings and a current development application for a new coal mine (Colton Coal Mine) attest to the prospectivity of the basin. Much of the area is also covered by active petroleum (including coal seam gas) and coal exploration tenements granted to several companies. The basin is of particular economic significance because resources are near major population centres, and there is an existing gas pipeline connection to the Port of Gladstone. Regional hydrogeological assessment of the Maryborough Basin was the primary focus of this investigation, and was required due to the lack of prior regional groundwater studies. Most previous hydrogeological work focused only around the main extraction area of the Bundaberg Groundwater Management Unit (GMU), in support of the local sugar cane industry. In addition, past studies have concentrated on the near-surface Cenozoic Elliott Aquifer, as it provides the bulk of groundwater extraction in the basin. Consequently, there is only limited data available on the hydrogeological properties and processes relevant to the deeper aquifers. This assessment involved compilation and synthesis of existing data and information (i.e., there was no new data acquisition undertaken), as well as new analytical studies to develop a basin-wide hydrostratigraphic framework and hydrogeological map. The overall objective was to improve conceptualisation of the regional groundwater system, and provide an up to date summary of existing knowledge of the basin’s aquifers and aquitards, to provide a base level of understanding about the hydrogeology of the basin in the event of any future development of coal or coal seam gas resources. A new regional hydrostratigraphic framework was developed for this project to incorporate the entire stratigraphic succession of the Maryborough Basin. This work defined nine regional hydrostratigraphic units (seven aquifers and two aquitards) on the basis of broadly similar hydrogeological parameters, with each unit having regionally consistent aquifer or aquitard characteristics. The distribution and thickness of each hydrostratigraphic unit can vary significantly across the basin, as shown on the new regional hydrogeology map (developed for this project). Understanding the spatial distribution of the hydrostratigraphic units is integral to understanding the basin-scale occurrence and characteristics of the regional hydrogeological flow systems. Regional hydrogeological characterisation of the Maryborough Basin iii The key aquifers in the Maryborough Basin (listed from youngest to oldest) are the: 1. Quaternary Coastal Aquifer; 2. Quaternary Alluvial Aquifer; 3. Quaternary Basalt Aquifer; 4. Elliott Aquifer (Cenozoic); 5. Burrum Aquifer (Cretaceous); 6. Grahams Creek Aquifer (Cretaceous); and 7. Duckinwilla Aquifer (Triassic to Jurassic). The regional aquitards in the Maryborough Basin are the Quaternary Coastal Aquitard and the Maryborough Aquitard (Cretaceous). The Elliott Aquifer is the main source of groundwater extracted from the Maryborough Basin, and commonly forms the uppermost hydrostratigraphic unit (the watertable aquifer). The Elliott Aquifer is an unconfined, semi-consolidated to consolidated aquifer consisting mainly of sand, silt and conglomerate. The aquifer contains discrete beds of gravel (usually in paleochannels incised into the underlying Burrum Coal Measures) that act as localised and highly transmissive conduits for relatively high volumes and rates of groundwater flow. Across the southern and central parts of the Maryborough Basin significant volumes of groundwater are extracted from the sandier sequences of the Cretaceous Burrum Aquifer. This unit, underlying the Elliot Aquifer, also contains coal measures that are the primary targets for current (and probably future) coal and CSG exploration. The unit is lithologically heterogeneous and groundwater is stored and transmitted both within fractures of the coal and silt-bearing strata, and also in intergranular pore space within sandstone sequences. Further work is required to distinguish the main hydraulically conductive water-bearing zones at a finer scale within this hydrostratigraphic unit. The Burrum Aquifer and the Elliott Aquifer are likely to be the most significantly affected by any future coal and CSG extraction in the basin. However, the magnitude, direction and focal zones for hydraulic connection (groundwater flow) between these two main aquifer systems are largely unknown, although current evidence suggests that there is no regionally extensive confining unit (e.g., aquitard) separating these aquifers. Increased groundwater extraction as a result of coal or CSG extraction from the Burrum Coal Measures could potentially affect the hydraulic processes that currently exist in these aquifers, and may have an adverse impact on beneficial uses, as a result of changes to existing groundwater flow patterns or aquifer water quality. Consequently,