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Browsing by Author "Raiber, M"

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Application of environmental isotopes to study aquifer interactions and their impact on groundwater salinisation in western Victoria
(Australian Institute of Nuclear Science and Engineering (AINSE), 2007-11) Raiber, M; Webb, JA; Jacobsen, GE; Chisari, R; Williams, AA; Neklapilova, B
Assessment of interaction between alluvial, volcanic and GAB aquifers using 3D visualisation and environmental tracers, Lockyer Valley, southeast Queensland, Australia
(Australian Geosciences Council, 2012-08-05) Raiber, M; Cox, ME; Cendón, DI; Hartland, A
A detailed 3D lithological model framework was developed using GOCAD software to understand interactions between alluvial, volcanic and GAB aquifers and the spatial and temporal distribution of groundwater recharge to the alluvium of the Lockyer Valley. Groundwater chemistry, isotope data (H20-δ2H and δ18O , 87Sr/86Sr, 3H and 14C) and groundwater level time-series data from approximately 550 observation wells were integrated into the catchment-wide 3D model to assess the recharge processes involved. This approach enabled the identification of zones where recharge to the alluvium primarily occurs from stream water during episodic flood events. Importantly, the study also demonstrates that in some sections of the alluvium recharge is also from storm rainfall and seepage discharge from the underlying GAB aquifers. These other sources of recharge are indicated by (a) the absence of a response of groundwater levels to flooding in some areas, (b) old radiocarbon ages, and (c) distinct bedrock water chemistry and δ2H and δ18O signatures in alluvial groundwater at these locations. Integration of isotopes, water chemistry and time-series displays of groundwater levels before and after the 2010/2011 flood into the 3D model suggest that the spatial variations in the alluvial groundwater response are mostly controlled by valley morphology and lithological (i.e. permeability) variations within the alluvium. Examination of the groundwater level variations in the 3D model also enabled quantification of the volumetric change of groundwater stored in the unconfined alluvial aquifer prior to and post-flood events.
Comparison of groundwater recharge estimation techniques in an alluvial aquifer system with an intermittent/ephemeral stream (Queensland, Australia)
(Springer Nature Limited, 2017-03-30) King, AC; Raiber, M; Cox, ME; Cendón, DI
This study demonstrates the importance of the conceptual hydrogeological model for the estimation of groundwater recharge rates in an alluvial system interconnected with an ephemeral or intermittent stream in south-east Queensland, Australia. The losing/gaining condition of these streams is typically subject to temporal and spatial variability, and knowledge of these hydrological processes is critical for the interpretation of recharge estimates. Recharge rate estimates of 76–182 mm/year were determined using the water budget method. The water budget method provides useful broad approximations of recharge and discharge fluxes. The chloride mass balance (CMB) method and the tritium method were used on 17 and 13 sites respectively, yielding recharge rates of 1–43 mm/year (CMB) and 4–553 mm/year (tritium method). However, the conceptual hydrogeological model confirms that the results from the CMB method at some sites are not applicable in this setting because of overland flow and channel leakage. The tritium method was appropriate here and could be applied to other alluvial systems, provided that channel leakage and diffuse infiltration of rainfall can be accurately estimated. The water-table fluctuation (WTF) method was also applied to data from 16 bores; recharge estimates ranged from 0 to 721 mm/year. The WTF method was not suitable where bank storage processes occurred. © 2017 Springer Nature Switzerland AG
Environmental isotopes meet 3D geological modelling: Conceptualising recharge and structurally-controlled aquifer connectivity in the basalt plains of south-western Victoria, Australia
(Elsevier B. V., 2015-08) Raiber, M; Webb, JA; Cendón, DI; White, PA; Jacobsen, GE
To develop a conceptual model of recharge and inter-aquifer connectivity for a complex aquifer system in southwestern Victoria, Australia, a three-dimensional (3D) geological model was constructed and used to examine the influence of the regional geology on groundwater composition and age, as well as recharge mechanisms. The major aquifers are three basalts, differentiated on age and geomorphological features, and an underlying palaeovalley (deep lead) system. The upper fine-grained sediments of the deep lead form an aquitard that separates the basalt from the permeable sands and gravels beneath. Recharge calculations (chloride mass balance and water-table fluctuation methods), salinity, stable isotope, tritium and radiocarbon data show that volcanoes and the youngest basalts, although volumetrically minor, form preferential recharge areas for all the basalts (up to ∼30 mm/year), and also recharge the deep lead sediments through volcanic necks that penetrate the aquitard. Infiltration through the thick, clay-rich soils on the older basalts is small (typically ⩽ 1–2 mm/year) and saline, resulting in a progressive increase of groundwater salinity along the flow path in these basalts. The comparison of fault location with groundwater age in the deep lead aquifer suggests that in some areas, faults exert significant structural control on groundwater flow. This study demonstrates the value of integrating geological, hydrogeological and hydrochemical data to identify preferential recharge areas, inter-aquifer connectivity and the influence of faults on groundwater flow in a complex aquifer system. © 2015 Elsevier B.V.
Groundwater chemistry baseline of the Walloon coal measures in the Clarence-Moreton and Surat basins, Queensland, Australia
(International Association of Hydrogeologists, 2013-09-19) Raiber, M; Cox, ME; Cendón, DI; Feitz, AJ
The Walloon Coal Measures (WCM) are a major target for coal seam gas exploration in the Surat and Clarence-Moreton basins in Queensland and New South Wales, Australia. It is now widely acknowledged that an improved understanding of the groundwater baseline is essential. Fundamental is determining the geological framework and an unbiased examination of the natural range, or baseline, of groundwater chemistry of the coal seams and adjacent aquifers. In order to determine the processes that control the spatial variability and evolution of groundwater chemistry, the chemistry baseline data of the WCM for the Surat and Clarence-Moreton basins are placed within the framework of a 3D geological model. In the assessment of the water chemistry baseline, four groundwater chemistry groups were identified from the hierarchical cluster analysis (HCA) which was applied to historical groundwater chemistry records from the Department of Natural Resources and Mines (DNRM) groundwater database. Each of these distinct groups contains groundwaters of a similar composition, which result from a number of different processes (e.g. groundwater recharge or interaction with other aquifers). However, groundwater of only one group has the typical composition of CSG waters, as documented by very high HCO3, and simultaneously low SO4, Ca and Mg concentrations, whereas the chemical composition of groundwater assigned to the other groups suggests that these follow a different evolutionary pathway. Following this initial screening, a total of ~60 samples was collected from the different groundwater chemistry groups for analysis of water chemistry (major, trace, rare earth elements and dissolved gases) and isotopic fingerprinting (d2H, d2H-CH4, d13C-DIC, d13C-CH4, d18O, 87Sr/86Sr,14CDIC and 36Cl/Cl). The analyses were combined with results from a similar groundwater chemistry study undertaken in the Surat Basin during 2009-2011 that aimed to establish a groundwater chemistry baseline for geological storage of CO2. The analyses of dissolved gases shows that there is a strong variability of dissolved CH4 concentration within groundwaters of the WCM, ranging from values below the reporting limit to ~50 mg/L. Likewise, isotope signatures and groundwater residence times within these coal-bearing sequence are highly variable spatially, reflecting the range of processes involved in groundwater evolution as well as the variable composition of these sedimentary rocks.
Groundwater mean residence times of a subtropical barrier sand island
(European Geosciences Union, 2020-03-19) Hofmann, H; Newborn, D; Cartwright, I; Cendón, DI; Raiber, M
Fresh groundwater on barrier islands is affected by changing sea levels and precipitation variability due to climate change and is also vulnerable to anthropogenic processes, such as contamination and groundwater over-abstraction. Constraining groundwater mean residence times (MRTs) and flow paths is essential for understanding and managing these resources. This study uses tritium (3H) and carbon-14 (14C) to determine the MRTs of groundwater along a transect across subtropical North Stradbroke Island, south-east Queensland, Australia. Hydraulic properties, major ion geochemistry and stable isotopes are used to validate residence times and to identify the processes responsible for their variability. 3H activities range from less than 0.01 to 1 TU (tritium units), which are values lower than those of local average rainfall (1.6–2.0 TU). 14C concentrations range from 62.5 to 111 pMC (percent modern carbon). Estimated MRTs determined using lumped parameter models and 3H activities range from 37 to more than 50 years. Recharge occurs over the entire island, and groundwater MRTs generally increase vertically and laterally towards the coastal discharge areas, although no systematic pattern is observed. MRTs estimated from 14C concentrations display similar spatial relationships but have a much greater range (from modern to approximately 5000 years). Water diversion and retention by lower-permeability units in the unsaturated parts of the dune systems are the most likely course for relatively long MRTs to date. The results indicate that the internal structures within the dune systems increase MRTs in the groundwater system and potentially divert flow paths. The structures produce perched aquifer systems that are wide-spread and have a significant influence on regional recharge. The geochemical composition of groundwater remains relatively consistent throughout the island, with the only irregularities attributed to old groundwater stored within coastal peat. The outcomes of this study enhance the understanding of groundwater flow, recharge diversion and inhibition for large coastal sand masses in general, especially for older sand masses that have developed structures from pedogenesis and dune movement. With respect to south-east Queensland, it allows the existing regional groundwater flow model to be refined by incorporating independent MRTs to test models' validity. The location of this large fresh groundwater reservoir, in dry and populous south-east Queensland, means that its potential to be used as a water source is always high. Background information on aquifer distribution and groundwater MRTs is crucial to better validate impact assessment for water abstraction. © Author(s) 2020
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
Hydrochemical and isotopic fingerprinting of the Walloon coal measures and adjacant aquifiers in the Clarence-Moreton and Eastern Basins in Southeast Queensland
(Geological Society of Australia, 2014-07-07) Raiber, M; Cendón, DI; Feitz, A; Sundaram, B; Suckow, A
The Clarence-Moreton Basin in New South Wales and Queensland is one of six nationwide priority regions where the potential impacts of future coal seam gas extractions and coal mining on water-dependent assets are being assessed through a national programme of Bioregional Assessments. The Clarence-Moreton Basin is an elongated intracratonic sag basin that contains sedimentary sequences of Middle and Late Triassic to Lower Cretaceous age with a combined thickness of up to approximately 3500 to 4000 m. Overlying the basin sedimentary sequences within the Clarence-Moreton bioregion (the eastwards draining part of the basin) are five major catchment systems (Lockyer Valley, Bremer/Warrill, Logan/Albert in Queensland, and the Richmond and Clarence river catchments in NSW), which host important alluvial groundwater and surface water resources that are intensively used for irrigation. In addition, these catchments host significant assets such as groundwater-dependant ecosystems (e.g. springs and wetlands). In order to predict the potential impacts of depressurisation associated with coal seam gas extraction from the Walloon Coal Measures (major target of CSG exploration in the Clarence-Moreton Basin), an accurate understanding of the links between different components of the hydrological system is essential. Prior to the development of numerical models, it is critical to describe potential connectivity pathways between deep and shallow aquifers, as well as interaction between groundwater and surface water. In order to assist with the development of reliable conceptual models that describe these interactions and constitute a road map to bioregional assessments, we have constructed a 3D geological model from elevation (DEM), stratigraphic, seismic and lithological data using GoCAD (Paradigm) 3D geological modelling software. The 3D geological model represents the major alluvial, sedimentary and volcanic aquifers and aquitards of the Clarence-Moreton bioregion. It helps to develop a more realistic understanding of the aquifer system behaviour, particularly if integrated with complementary data sources such as water level or hydrochemical data, and it will provide the geometric framework for the groundwater numerical model. The 3D geological model highlights the structural complexity of the Clarence-Moreton Basin, with significant vertical displacements of major basin units of several hundred meters registered along major regional fault systems, and abutments of stratigraphic units against basement ridges or pinching out of units observed in different parts of the basin. These observed structural features and the geometric characteristics of aquifers/aquitards can have a significant influence on potential connectivity pathways. For example, the thinning of the Gatton Sandstone against the underlying Woogaroo Subgroup at the basin margin in the Lockyer Valley results in upwards seepage of groundwater from the Gatton Sandstone into the alluvial aquifer, and this upwards discharge probably also feeds wetlands located along the northern margin of the Gatton Sandstone.
Hydrochemical processes in a shallow coal seam gas aquifer and its overlying stream–alluvial system: implications for recharge and inter-aquifer connectivity
(Elsevier, 2015-10-01) Duvert, C; Raiber, M; Owen, DDR; Cendón, DI; Batiot-Guilhe, C; Cox, ME
In areas of potential coal seam gas (CSG) development, understanding interactions between coal-bearing strata and adjacent aquifers and streams is of highest importance, particularly where CSG formations occur at shallow depth. This study tests a combination of hydrochemical and isotopic tracers to investigate the transient nature of hydrochemical processes, inter-aquifer mixing and recharge in a catchment where the coal-bearing aquifer is in direct contact with the alluvial aquifer and surface drainage network. A strong connection was observed between the main stream and underlying alluvium, marked by a similar evolution from fresh Ca–Mg–HCO3 waters in the headwaters towards brackish Ca–Na–Cl composition near the outlet of the catchment, driven by evaporation and transpiration. In the coal-bearing aquifer, by contrast, considerable site-to-site variations were observed, although waters generally had a Na–HCO3–Cl facies and high residual alkalinity values. Increased salinity was controlled by several coexisting processes, including transpiration by plants, mineral weathering and possibly degradation of coal organic matter. Longer residence times and relatively enriched carbon isotopic signatures of the downstream alluvial waters were suggestive of potential interactions with the shallow coal-bearing aquifer. The examination of temporal variations in deuterium excess enabled detection of rapid recharge of the coal-bearing aquifer through highly fractured igneous rocks, particularly at the catchment margins. Most waters collected from the coal-bearing aquifer also showed an enhanced influence of weathering during the wet season, which was likely triggered by the water–rock interaction with fresh recharge waters. An increase in both residual alkalinity and carbon isotopic ratios at two locations indicated inter-aquifer mixing between alluvium and bedrock during the wet season. The results of this study emphasise the need for conducting baseline hydrochemical surveys prior to CSG development in order to describe the transient nature of recharge and inter-aquifer mixing processes. © 2015, Elsevier Ltd.
Identifying flood recharge and inter-aquifer connectivity using multiple isotopes in subtropical Australia
(Copernicus Publications, 2015-05-19) King, AC; Raiber, M; Cendón, DI; Cox, ME; Hollins, SE
An understanding of hydrological processes is vital for the sustainable management of groundwater resources, especially in areas where an aquifer interacts with surface water systems or where aquifer interconnectivity occurs. This is particularly important in areas that are subjected to frequent drought/flood cycles, such as the Cressbrook Creek catchment in Southeast Queensland, Australia. In order to understand the hydrological response to flooding and to identify inter-aquifer connectivity, multiple isotopes (δ2H, δ18O, 87Sr/86Sr, 3H and 14C) were used in this study in conjunction with a comprehensive hydrochemical assessment, based on data collected 6 months after severe flooding in 2011. The relatively depleted stable isotope signatures of the flood-generating rainfall (δ2H: −30.2 to −27.8‰, δ18O: −5.34 to −5.13‰ VSMOW) were evident in surface water samples (δ2H: −25.2 to −23.2‰, δ18O: −3.9 to −3.6‰ VSMOW), indicating that these extreme events were a major source of recharge to the dam in the catchment headwaters. Furthermore, stable isotopes confirmed that the flood generated significant recharge to the alluvium in the lower part of the catchment, particularly in areas where interactions between surface waters and groundwater were identified and where diffuse aquifer recharge is normally limited by a thick (approximately 10 m) and relatively impermeable unsaturated zone. However, in the upper parts of the catchment where recharge generally occurs more rapidly due to the dominance of coarse-grained sediments in the unsaturated zone, the stable isotope signature of groundwater resembles the longer-term average rainfall values (δ2H: −12.6, δ18O: −3.4‰ VSMOW), highlighting that recharge was sourced from smaller rainfall events that occurred subsequent to the flooding. Interactions between the bedrock aquifers and the alluvium were identified at several sites in the lower part of the catchment based on 87Sr/86Sr ratios; this was also supported by the hydrochemical assessment, which included the modelling of evaporation trends and saturation indices. The integrated approach used in this study facilitated the identification of hydrological processes over different spatial and temporal scales, and the method can be applied to other complex geological settings with variable climatic conditions.© 2015, Author(s).
Isoscapes: a 3D visualisation approach to study aquifer connectivity during drought and flood, Lockyer Valley, southeast Queensland, Australia,
(International Association of Hydrogeologists, 2013-09-16) Raiber, M; Cox, ME; Cendón, DI; Hartland, A; James, A
A 3D geological model of the Lockyer Valley, southeast Queensland, was developed using GOCAD software as a framework to study interactions between alluvial, basaltic and sedimentary bedrock aquifers of the Clarence-Moreton Basin and the spatial and temporal variability of recharge to the alluvium. The isotopic data (δ2h and δ18O, 87Sr/86Sr, 3H and 14C), water chemistry and time-series of groundwater levels before and after the 2010/2011 flood, were integrated within the 3D hydrogeological framework using Groundwater Visualisation System (GVS). Groundwater “isoscapes" (i.e. isotopic landscapes) were developed by spatial interpolation of isotopic results from more than 180 bores to enable the identification of different sources of water that contribute to recharge. The isotopic parameters are displayed as colour-contoured surfaces of the different aquifers and as coloured cylinders of variable thickness marking the position and thickness of the screened interval. Interpretation of isotopic values and their spatial relationships show that recharge to the alluvium primarily occurs from streams following episodic flood events. However, importantly, the study also demonstrates that in some sections of the alluvial plain, recharge to the alluvium is derived from both diffuse rainfall recharge and seepage discharge from the underlying Great Artesian Basin (GAB) aquifers. Bedrock seepage recharge dominates in some parts of the alluvial aquifer during droughts, enhanced by continuous pumping of the alluvial aquifer during the drought, as indicated by overall longer groundwater residence times, and high groundwater salinities. In addition, the hydrochemical signature of recharge from the bedrock is characterised by an isotopic depletion of δ2H and δ18O, and more radiogenic 87Sr/86Sr ratios in alluvial groundwater. The spatial variability of the responses is mostly controlled by catchment morphology and lithological (i.e. permeability) variations within the alluvium. Assessment of the unconfined groundwater levels in the 3D geological model enabled quantification of the volumetric change of groundwater stored in the alluvial aquifer system before and after flood events.
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
Multi-tracer approach to investigate groundwater recharge and aquifer connectivity in the Clarence-Moreton and eastern Surat basins in southeast Queensland
(National Centre for Groundwater Research And Training, 2015-11-03) Raiber, M; Feitz, A; Cendón, DI; Suckow, A
The Walloon Coal Measures (WCM) in the Clarence-Moreton and the Surat basins in QLD and northern NSW contain up to approximately 600 m of mudstone, siltstone, sandstone and coal. Wide-spread exploration for coal seam gas (CSG) within both basins has led to concerns that the depressurisation associated with the resource development may impact on water resources in adjacent aquifers. In order to predict potential impacts, a detailed understanding of sedimentary basins hydrodynamics that integrates geology, hydrochemistry and environmental tracers is important. In this study, we show how different hydrochemical parameters and isotopic tracers (i.e. major ion chemistry, dissolved gas concentrations, δ2H and δ13C of CH4, δ13C-DIC, δ18O, δ2H, 87Sr/86Sr, 3H, 14C and 36Cl) can help to improve the knowledge on groundwater recharge and flow patterns within the coal-bearing strata and their connectivity with over- or underlying formations. Dissolved methane concentrations in groundwaters of the WCM in the Clarence-Moreton Basin range from below the reporting limit (10 μg/L) to approximately 50 mg/L, and samples collected from nested bore sites show that there is also a high degree of vertical variability within the aquifer. Other parameters such as 3H, δ13C & 14C in DIC collected along assumed flow paths are also highly variable, which indicates local groundwater flow cells rather than regional flow. In contrast, 87Sr/86Sr isotope ratios of WCM groundwaters are very uniform and distinct from groundwaters contained in other sedimentary bedrock units. This suggests that 87Sr/86Sr ratios may be a suitable tracer to study hydraulic connectivity of the Walloon Coal Measures with over- or underlying aquifers, although more studies on the systematic are required. Overall, the complexity of recharge processes, aquifer connectivity and within-formation variability confirms that a multi-tracer approach is required to understand aquifer connectivity in these sedimentary basins.
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.
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.
Seasonal and spatial variations in rare elements to identify inter-aquifer linkages and recharge processes in an Australian catchment
(Elsevier B. V., 2015-03-09) Duvert, C; Cendón, DI; Raiber, M; Seidel, JL; Cox, ME
With the aim of elucidating the seasonal behaviour of rare earth elements (REEs), surface and groundwaters were collected under dry and wet conditions in different hydrological units of the Teviot Brook catchment (Southeast Queensland, Australia). Sampled waters showed a large degree of variability in both REE abundance and normalised patterns. Overall REE abundance ranged over nearly three orders of magnitude, and was consistently lower in the sedimentary bedrock aquifer (18ppt<∑REE<477ppt) than in the other hydrological systems studied. Abundance was greater in springs draining rhyolitic rocks (∑REE=300 and 2054ppt) than in springs draining basalt ranges (∑REE=25 and 83ppt), yet was highly variable in the shallow alluvial groundwater (16ppt<∑REE<5294ppt) and, to a lesser extent, in streamwater (85ppt<∑REE<2198ppt). Generally, waters that interacted with different rock types had different REE patterns. In order to obtain an unbiased characterisation of REE patterns, the ratios between light and middle REEs (R(M/L)) and the ratios between middle and heavy REEs (R(H/M)) were calculated for each sample. The sedimentary bedrock aquifer waters had highly evolved patterns depleted in light REEs and enriched in middle and heavy REEs (0.17
Significance of the connection between bedrock, alluvium and streams: a spatial and temporal hydrogeological and hydrogeochemical assessment from Queensland, Australia
(Elsevier B. V., 2019-02) Raiber, M; Lewis, S; Cendón, DI; Cui, T; Cox, ME; Gilfedder, M; Rassam, DW
Catchment-scale hydrological and hydrogeological investigations commonly conclude by finding that particular stream reaches are either gaining or losing; they also often assume that the influence of bedrock aquifers on catchment water balances and water quality is insignificant. However, in many cases, such broad findings are likely to oversimplify the spatial and temporal complexity of the connections between the different hydrological system components, particularly in regions dominated by cycles of droughts and flooding. From a modelling perspective, such oversimplifications can have serious implications on the process of identifying the magnitude and direction of the exchange fluxes between the surface and groundwater systems. In this study, we use 3D geological modelling and historic water chemistry and hydraulic records to identify the origins of groundwater at different locations in the alluvium and along the course of streams in the Lockyer Valley (Queensland, Australia), a catchment impacted by a severe drought (‘Millennium Drought’) from 1998 to 2009, followed by extensive flooding in 2011. We also demonstrate how discharge from the sub-alluvial regional-scale volcanic and sedimentary bedrock influences the water balance and water quality of the alluvium and streams. The investigation of aquifer geometry via development of a three-dimensional geological model combined with an assessment of hydraulic data provided important insights on groundwater flow paths and helped to identify areas where bedrock aquifers interact with shallow alluvial aquifers and streams. Multivariate statistical techniques were then applied as an additional line of evidence to groundwater and surface water hydrochemical data from large historical datasets. This confirmed that most sub-catchments within the Lockyer Valley have distinct water chemistry patterns, which result from mixing of different water sources, including discharge from the sub-alluvial bedrock. Importantly, in addition to the observed spatial variability, time-series hydrochemical groundwater and surface water data further demonstrated that the hydraulic connection between alluvial aquifers, streams and sub-alluvial bedrock aquifers is temporally dynamic with very significant changes occurring at the transition from normal to drought conditions and following flooding, affecting both catchment water quality and water balances. Crown Copyright © 2018 Published by Elsevier B.V.
Time-series of tritium, stable isotopes and chloride reveal short-term variations in groundwater contribution to a stream
(Hydrological Earth Systems Sciences, 2016-01-18) Duvert, C; Stewart, MK; Cendón, DI; Raiber, M
A major limitation to the assessment of catchment transit time (TT) stems from the use of stable isotopes or chloride as hydrological tracers, because these tracers are blind to older contributions. Yet, accurately capturing the TT of the old water fraction is essential, as is the assessment of its temporal variations under non-stationary catchment dynamics. In this study we used lumped convolution models to examine time series of tritium, stable isotopes and chloride in rainfall, streamwater and groundwater of a catchment located in subtropical Australia. Our objectives were to determine the different contributions to streamflow and their variations over time, and to understand the relationship between catchment TT and groundwater residence time. Stable isotopes and chloride provided consistent estimates of TT in the upstream part of the catchment. A young component to streamflow was identified that was partitioned into quickflow (mean TT  ≈  2 weeks) and discharge from the fractured igneous rocks forming the headwaters (mean TT  ≈  0.3 years). The use of tritium was beneficial for determining an older contribution to streamflow in the downstream area. The best fits between measured and modelled tritium activities were obtained for a mean TT of 16–25 years for this older groundwater component. This was significantly lower than the residence time calculated for groundwater in the alluvial aquifer feeding the stream downstream ( ≈  76–102 years), emphasising the fact that water exiting the catchment and water stored in it had distinctive age distributions. When simulations were run separately on each tritium streamwater sample, the TT of old water fraction varied substantially over time, with values averaging 17 ± 6 years at low flow and 38 ± 15 years after major recharge events. This counterintuitive result was interpreted as the flushing out of deeper, older waters shortly after recharge by the resulting pressure wave propagation. Overall, this study shows the usefulness of collecting tritium data in streamwater to document short-term variations in the older component of the TT distribution. Our results also shed light on the complex relationships between stored water and water in transit, which are highly non-linear and remain poorly understood. © Author(s) 2016. CC Attribution 3.0 License.
Understanding groundwater dynamics on barrier islands using geochronological data: an example from North Stradbroke Island, South-east Queensland
(National Centre for Groundwater Research And Training, 2015-11-03) Hofmann, H; Newborn, D; Cartwright, I; Cendón, DI; Raiber, M
Freshwater lenses underneath barrier islands are dynamic systems affected by changing sea levels and groundwater use. They are vulnerable to contamination and over-abstraction. Residence times of fresh groundwater in barrier islands are poorly understood and have mostly been assessed by modelling approaches and estimates without fundamental validation with chronological estimations. Assessing residence time and recharge rates will improve significantly our understanding of hydrological processes of coastal environments that will in turn allow us to make informed decisions on groundwater use and environmental protection. This project focused on groundwater recharge rates and residence times of the fresh water aquifer system of North Stradbroke Island, south-east Queensland, Australia. Groundwater bores, wetlands and submarine groundwater discharge points in the tidal areas (wonky holes) were sampled along a transect across the island and were analysed for major ion chemistry and stable isotopes (δ2H, δ18O, δ13C) in combination with 3H, 14C analysis and 222Rn. Calculated 3H using a 90% exponential-piston flow model and 14C ages range from 12 to >100 years and modern to 3770 years, respectively, indicating a highly heterogeneous aquifer system with mixing from low and high conductive areas. The major ion chemistry in combination with stable and radiogenic isotopes suggests that a significant groundwater component derives from the fractured rock basement and older sedimentary formations underlying the sand dunes of the island. The results help refining the conceptual and numerical groundwater flow model for North Stradbroke Island in this particular case but also demonstrate the possible complexity of barrier island hydrogeology.
Use of multi-isotope surveys to identify bedrock-alluvium interactions, Cressbrook Creek Catchment, southeast Queensland
(International Association of Hydrogeologists, 2013-09-19) King, AC; Raiber, M; Cendón, DI; Cox, ME
Radiocarbon (14C) is commonly used to study groundwater residence times, but the interpretation of results is often subject to a high degree of uncertainty due to interaction with modern and ‘dead carbon’, especially for relatively young groundwater or groundwater that has interacted with organic material. To address this concern, 87Sr/86Sr ratios, δ2H and δ18O, combined with tritium and radiocarbon are used to identify zones where older bedrock water recharges the alluvial aquifer of the Cressbrook Creek catchment in southeast Queensland. Cressbrook Creek is an intermittent stream that is primarily recharged by groundwater in the upper catchment. The alluvial system overlies variable bedrock with metamorphic rocks, rhyolites and granites in the headwaters, and sedimentary sequences (mostly sandstones) downstream. The catchment has largely been dry during a decade of drought, but has owed continuously since 2010 and experienced severe flooding in January 2011. Groundwater samples collected from alluvial and bedrock aquifers in June 2011 were analysed for a range of environmental tracers. Six alluvial waters were analysed for 14C; of these, four are modern. The other two samples have pMC values of 88.0 and 81.1 (uncorrected ages of 1,045 and 1,680 years; Sites A and B, respectively) whereas tritium analyses indicate an age of less than 100 years for the same samples. This disparity in groundwater ages may have been caused by: 1) seepage of older bedrock groundwater into the alluvium; or 2) carbonate dissolution processes. Therefore, evidence from other tracers, including 87Sr/86Sr, was assessed as an independent constraint to support the conceptual understanding of aquifer interactions. Alluvial groundwater from Site A has an enriched 87Sr/86Sr signature, indicating that it has probably received recharge from the underlying granite aquifer. Groundwater from Site B has a lower 87Sr/86Sr ratio than the other alluvial groundwaters, which indicates this site probably received recharge from the underlying sandstone aquifer.

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