Noble gas tracers: improving the understanding of groundwater recharge and flow systems in Australia
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Date
2019-12-14
Journal Title
Journal ISSN
Volume Title
Publisher
American Geophysical Union (AGU)
Abstract
Australia has several large sedimentary basins, including the Great Artesian Basin (GAB), one of the largest aquifer systems in the world, which has a long history of groundwater extraction for stock, agriculture and urban water supplies. With the recent onset of exploration and development for coal bed methane and shale gas and the extension of existing and approval of new mining operations, there is a need to characterise recharge processes and flow dynamics in these complex aquifer systems to assess cumulative impacts, develop policy for groundwater use and underpin the social licence to operate for extractive industries. We present examples of two sedimentary basins where noble gas tracers have been used in combination with other environmental tracers and show how the noble gas tracers provided critical insights into groundwater system understanding. In the eastern recharge areas of the GAB, 14C and 36Cl results highlighted the existence of two different flow areas with very different recharge mechanisms. Although these isotope systems yielded the qualitative results in a relatively straightforward manner, the isotopes 85Kr and 81Kr provided much more reliable results than 14C and 36Cl, for which detailed geochemical corrections were needed, and the application of noble gases therefore helped to reduce the conceptual uncertainties associated with previous ‘conventional’ tracer studies. The Beetaloo Sub-Basin, located in the Northern Territory, contains aquifer systems that cover hundreds of square kilometres. The karstic and heterogeneous structure of the shallow aquifers, and associated recharge characteristics that are variable in season, latitude and local structures, poses many challenges for the characterisation of groundwater flow and recharge. Conventional tracers demonstrate obvious contradictions such as an increase of 14C down the hydraulic gradient, and modern waters according to the gas tracers CFC, SF6 and H1301, combined with negligible tritium. The noble gases provided insights into the recharge mechanisms, elucidating the challenges within the rest of the dataset, and suggest that 39Ar might be very useful as it covers a unique age range that is important for better understanding the system.
Description
Keywords
Rare gases, Tracer techniques, Groundwater recharge, Flow, Artesian basins, Northern Territory, Aquifers, Australia
Citation
Deslandes, A., Suckow, A. O., Gerber, C., Wilske, C., Mallants, D., Raiber, M., & Meredith, K. (2019). Noble gas tracers: improving the understanding of groundwater recharge and flow systems in Australia. Poster presented at the AGU Fall Meeting 2019, San Francisco, California, USA, 9-13 December 2019. Retrieved from: https://agu-do03.confex.com/agu/fm19/meetingapp.cgi/Paper/574263