Browsing by Author "Gerber, C"

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    Groundwater recharge at the eastern intake beds of the Great Artesian Basin using multi-isotope studies
    (National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-25) Sucknow, A; Deslandes, A; Gerber, C; Taylor, A; Raiber, M; Barrett, D; Meredith, KT
    Objectives: Large sedimentary basins with multiple aquifer systems, such as the Great Artesian Basin (GAB) in Australia, are difficult to study because of the very large time scales associated with groundwater flow. The GAB is the world’s largest and deepest artesian groundwater basin and has become increasingly stressed due to demand from multiple competing industries (agriculture, oil, coal and gas). Quantifying groundwater recharge is crucial for understanding the water balance for this economically and culturally important multi-aquifer system. The complexity of the GAB can only be dealt with by applying multiple lines of evidence including environmental isotopes, supported by hydrochemical, sedimentological, and geophysical observations. Design and Methodology: Three studies on the recharge areas of the GAB investigated recharge to the Hutton Sandstone and the Precipice Sandstone (QLD) and the Pilliga Sandstone (NSW). Multiple environmental tracers (major ion chemistry, 18O, 2H, 3H, 13C, 14C, 36Cl, 87Sr/86Sr, 85Kr, 81Kr, noble gases) were measured. Recharge rates were derived from tracer concentration profiles and aquifer cross-sections with porosity derived from previous studies. Conclusions: Tracer results in the Precipice Sandstone are consistent with pumping test data and re-injection of coal seam gas produced water, suggesting high hydraulic conductivities. They provided the first estimate of average long-term annual recharge to this deep confined aquifer, which is of a similar order of magnitude as today’s industrial re-injection of CSG water. © The Authors
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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.
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    Quantifying recharge to the Pilliga Sandstone aquifer, Great Artesian Basin Australia: learnings from combining 14C, 36Cl and 81Kr
    (Goldschmidt, 2022-07-12) Sucknow, AO; Raiber, M; Deslandes, A; Gerber, C; Martinez, J; Yang, GM; Jiang, W; Meredith, KT
    The Pilliga Sandstone in the Coonamble Embayment in New South Wales, Australia, is part of the Great Artesian Basin (GAB), an aquifer system that underlies 22% of the Australian continent and is one of the main freshwater resources of inland Australia. Despite its significance, groundwater recharge to the Pilliga Sandstone is insufficiently constrained. Better quantifying recharge is particularly important because of competing interests between agriculture and other industries. The petroleum industry proposes to extract coal seam gas from the Gunnedah Basin underlying the Pilliga Sandstone. Groundwater flow in the Pilliga Sandstone is from the outcrops in the East (light blue in the Figure) to the West. Here we present results of a multi-tracer study (hydrochemistry, 2H, 3H, 3He/4He, 13C, 18O, 14C, 36Cl, 40Ar/36Ar, 85Kr, 81Kr, 87Sr/86Sr and noble gases) that were complemented in the northern part of the project area by geophysical investigations (seismic and ground-based electromagnetics). The project area shows a distinct southern flow path (Figure) for which groundwater velocity and therefore recharge could be quantified using 14C and 36Cl, where the rates were further improved by 81Kr. In the northern area the application of 14C and 36Cl was unsuccessful because of an admixture of waters from the underlying Gunnedah Basin. Groundwaters in that basin, containing the formations targeted for the CSG exploration, show very high total dissolved inorganic carbon (up to 300mMol/L) and chloride concentrations (up to 2000mg/L). Further groundwater from the Gunnedah Basin and intermediate layers to the Pilliga Sandstone has 40Ar/36Ar ratios up to 432, the highest values found in Australian groundwater so far, probably indicating partial release from old sediments by intruding dykes as indicated by a correlation with 3He/4He. Small volumes of admixtures of this water discharge into the Pilliga Sandstone and overprint the age information of the 14C and 36Cl values. Given the success of 81Kr in constraining flow rates for the southern flow path, there is great potential for 81Kr to also improve flow rate estimates in the northern flow area, but access to bores at intermediate distances of the northern flow path have to-date been denied.