Browsing by Author "Mallants, D"

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    Multi-isotope studies investigating recharge and inter-aquifer connectivity in coal seam gas areas (Qld, NSW) and shale gas areas (NT)
    (CSIRO Publishing, 2020-05-15) Suckow, A; Deslandes, A; Gerber, C; Lamontagne, S; Mallants, D; Davies, P; Taylor, A; Wilske, C; Smith, S; Raiber, M; Meredith, KT; Rachakonda, PK; Larcher, A; Wilkes, P; Prommer, H; Siade, A; Barrett, D
    Large sedimentary basins with multiple aquifer systems like the Great Artesian Basin and the Beetaloo Sub-Basin are associated with large time and spatial scales for regional groundwater flow and mixing effects from inter-aquifer exchange. This makes them difficult to study using traditional hydrogeological investigation techniques. In continental onshore Australia, such sedimentary aquifer systems can also be important freshwater resources. These resources have become increasingly stressed because of growing demand and use of groundwater by multiple industries (e.g. stock, irrigation, mining, oil and gas). The social licence to operate for extractive oil and gas industries increasingly requires robust and reliable scientific evidence on the degree to which the target formations are vertically and laterally hydraulically separated from the aquifers supplying fresh water for stock and agricultural use. The complexity of such groundwater interactions can only be interpreted by applying multiple lines of evidence including environmental isotopes, hydrochemistry, hydrogeological and geophysical observations. We present an overview of multi-tracer studies from coal seam gas areas (Queensland and New South Wales) or areas targeted for shale gas development (Northern Territory). The focus was to investigate recharge to surficial karst and deep confined aquifer systems before industrial extraction on time scales of decades up to one million years and aquifer inter-connectivity at the formation scale. A systematic and consistent methodology is applied for the different case study areas aimed at building robust conceptual hydrogeological models that inform groundwater management and groundwater modelling. The tracer studies provided (i) in all areas increased confidence around recharge estimates, (ii) evidence for a dual-porosity flow system in the Hutton Sandstone (Queensland) and (iii) new insights into the connectivity, or lack thereof, of flow systems. © CSIRO 2020
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    Noble gas tracers: improving the understanding of groundwater recharge and flow systems in Australia
    (American Geophysical Union (AGU), 2019-12-14) Deslandes, A; Suckow, A; Gerber, C; Wilske, C; Mallants, D; Raiber, M; Meredith, KT
    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.