Browsing by Author "Cendón, DI"
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- Item14C activity of DIC and DOC within a clayey-silt aquitard(University of New South Wales and Australian Nuclear Science and Technology Organisation, 2015-07-10) Timms, W; Hartland, A; Jacobsen, GE; Cendón, DI; Crane, R; McGeeney, DNot provided to ANSTO Library.
- ItemA 35 ka record of groundwater recharge in south-west Australia using stable water isotopes(Elsevier B. V., 2020-05-15) Priestley, SC; Meredith, KT; Treble, PC; Cendón, DI; Griffiths, AD; Hollins, SE; Baker, AA; Pigois, JPThe isotopic composition of groundwater can be a useful indicator of recharge conditions and may be used as an archive to infer past climate variability. Groundwater from two largely confined aquifers in south-west Australia, recharged at the northernmost extent of the westerly wind belt, can help constrain the palaeoclimate record in this region. We demonstrate that radiocarbon age measurements of dissolved inorganic carbon are appropriate for dating groundwater from the Leederville aquifer and Yarragadee aquifer within the Perth Basin. Variations in groundwater δ18O values with mean residence time were examined using regional and flow line data sets, which were compared. The trends in the regional groundwater data are consistent with the groundwater flow line data supporting the hypothesis that groundwater δ18O is a robust proxy for palaeo-recharge in the Perth Basin. A comparison between modern groundwater and rainfall water isotopes indicates that recharge is biased to months with high volume and/or intense rainfall from the westerly wind circulation and that this has been the case for the last 35 ka. Lower stable water isotope values are interpreted to represent recharge from higher volume and/or more intense rainfall from 35 ka through the Last Glacial Maximum period although potentially modulated by changes in recharge thresholds. The Southern Perth Basin groundwater isotopic record also indicates a trend towards higher volume and/or intense rainfall during the Mid- to Late Holocene. The long-term stable water isotope record provides an understanding of groundwater palaeo-recharge. Knowledge of recharge dynamics over long time scales can be used to improve current water sharing plans and future groundwater model predictions. © Crown Copyright 2019
- ItemA 35 ka record of groundwater recharge using stable water isotopes for Perth Basin in south-west Australia(National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-25) Priestley, SC; Meredith, KT; Treble, PC; Cendón, DI; Griffiths, AD; Hollins, SE; Baker, AA; Pigois, JPObjectives: As most large groundwater basins can contain ‘old’ groundwater where extraction exceeds groundwater recharge, knowledge of the past conditions and timing under which groundwater was recharged is needed to sustainably manage groundwater resources. Moreover, the isotopic composition of groundwater can be a useful indicator of rainfall isotope compositions and help to determine the drivers and impacts of rainfall and climate change. Applying isotopic tools to groundwater contained in regional aquifer systems can provide low-resolution information on recharge intensity, recharge source and past climatic conditions for the region. Design and Methodology: A dataset containing groundwater ages (14CDIC) and stable isotopes of water (δ18O and δ2H) from two regional groundwater systems within the Perth Basin, the Leederville Formation and Yarragadee Formation, were compiled to create a low-resolution palaeo-archive of groundwater recharge. Original data and results: The trends in stable isotopes of water over time in the regional groundwater data are consistent with groundwater flow line data supporting our hypothesis that groundwater stable isotopes are a proxy for palaeo-recharge. A comparison between modern groundwater and rainfall water isotopes indicates that recharge is biased to months with high volume and/or intense rainfall from the westerly wind circulation and that this has been the case for the last 35 ka. Lower stable water isotope values are interpreted to represent recharge from higher volume and/or more intense rainfall from 35 ka through the Last Glacial Maximum period although potentially modulated by changes in recharge thresholds. Conclusion: The groundwater isotope record is interpreted to be a low-resolution archive of recharge driven by changes in the relative intensity of past rainfall and recharge thresholds. This long-term stable isotopic recharge record provides a greater understanding of groundwater palaeo-recharge, and the connection between recharge and climate in the past. © The Authors
- ItemA 50 ka hydrological record from northern Australia inferred from the chemistry of ostracod valves: implications for the Australian monsoon(18th INQUA Congress, 2011-07-21) Devriendt, D; Chivas, AR; Cendón, DIMost continuous records of environmental changes on continents over the last glacial cycle derive from the study of lake sediments. Such records are uncommon in Australia since lakes rarely remained permanent features over long periods of time. During most of the last glacial cycle, the largest lake on the Australian continent was located in the centre of the Carpentaria basin, an area covered by the sea today. The well preserved lacustrine sequence underlying the modern marine sediment of the Gulf of Carpentaria has been studied extensively in the past with the main phases of environmental changes with regard to marine versus non-marine conditions being well established. However, palaeoclimatic inferences during the lacustrine phase have remained challenging due to periodic marine influences, strong seasonality and the poor preservation of the lacustrine sequence at sites away from the depocentre of the basin. The elemental (Ca/Na/Mg/Sr/Ba/Mn/Fe/U) and isotopic (δ18O and δ13C) compositions of ostracod valves from the Gulf of Carpentaria lacustrine sequence provide a new palaeohydrological record for northern Australia covering the period 64-14 ka. In particular, inferences on the contributions of potential water sources to the palaeolake and their variations through time are drawn by comparing the ostracod Na/Sr/Ba relative concentrations to the chemical signatures of the rivers draining the modern Carpentaria basin. Wide climatic variations were recorded by the ostracod chemical and isotopic composition and reflect the changing state of the Australian monsoon through time. The monsoon appears weaker/absent during the LGM, although irregular precipitation patterns during this time provoked the oscillations of the palaeolake water-level. Immediately after the LGM, the monsoon progressively developed over northern Australia until 14 ka BP. This causes the rivers from the far south of the basin to reconnect with the palaeolake.
- ItemAccumulative evidence highlighting that the Narrabri and Gunnedah formations are mythical(National Centre for Groundwater Research And Training, 2017-07-12) Kelly, BFJ; Cendón, DI; Iverach, CP; Harris, SJ; Hankin, SIThe Narrabri and Gunnedah Formations, used to describe the valley-filling sedimentary sequences in portions of the Murray-Darling Basin, have never been formally defined. The hydrogeological evidence for naming these formations is reviewed in the context of modern sedimentary models. Are we using the right architectural model? Hundreds of lithological logs from the Murrumbidgee, Namoi, and Gwydir catchments are used to examine the evolution of each alluvial aquifer. For each depth interval, the catchment-wide proportions of coarse (gravel, sand) and fine (silt, clay) sediments is determined. Sediment size distributions are then examined in the context of past climates and the conceptual inland fluvial model for distributive fluvial systems. Vertical hydraulic connectivity is examined using new hydrogeochemical data and nested groundwater hydrograph sets. All systems show the core features of aggradational distributive fluvial systems. The valley-filling sequences for all catchments examined transitioned from high energy wet environments at depth, dominated by sand and gravel deposits, through to the modern-day low-energy silt and clay dominated depositional environments. Gravel and sand deposits dominate in the proximal portion of the catchment, and low energy silt and clay deposits dominate in the distal portions. The apparent existence of the Narrabri and Gunnedah Formations is due to changing sediment grain size proportion and channel fill sand connectivity. Both the facies and hydrograph analyses show that semi-confining layers are only local. Extensive hydrogeochemical data from the Namoi catchment show continuity of mixing between basement and surface inflows. All catchments have many sedimentary architectural features consistent with the distributive fluvial system model, and reflect changing climate throughout the Neogene and Quaternary. Use of the Narrabri and Gunnedah Formation nomenclature, which has been incorporated into the National Aquifer Framework, is not supported by either the sedimentological, hydrograph or hydrogeochemical record.
- Item‘Age’, recharge rates and connectivity of groundwater in deeper aquifers of the Sydney Basin(Geological Society of Australia, 2014-07-07) Kermode, SJ; Cendón, DI; Hankin, SI; Russell, GThe Permo-Triassic Sydney Basin covers almost 50 000 km2 and extends from the outer continental shelf inland to the Great Diving Range, from Newcastle in the north to Batemans Bay in the south. Major lithological units broadly include the Permian Coal Measures, the Permo-Triassic Narrabeen Group, the Triassic Hawkesbury Sandstone and the Wianamatta Shale. The Hawkesbury Sandstone is generally made of very thick heavily compacted quartz sands, with minor discontinuous shale units. Its aquifer system is a complex, dual porosity, deep fractured system with three aquifers typically recognised. The shallow and intermediate aquifers contribute to spring and base stream flows as well as groundwater dependent ecosystems, and the deep regional aquifer system. It is this deeper system that is investigated in this study. Groundwater from the Sydney Basin, and in particular Hawkesbury Sandstone aquifers, forms part of emergency supply strategies for coping with future severe droughts, with >5 million people living in the region, in addition to large industrial development. Despite the significance of these resources there are still large gaps in our knowledge of these aquifers including aspects such as age recharge and mixing rates. Filling these knowledge gaps has become even more critical in order to understand impacts of existing and planned coal and coal seam gas (CSG) mining of the underlying Illawarra Coal Measures. Community concerns over risks associated with CSG extraction have reached fever pitch in recent years, and there is public demand for research into these aquifers. Understanding of these systems has been complicated by the poor quality of existing data – commonly relying solely on driller bore-logs, reporting only being carried out for specific mine or extraction activities, and therefore conducted over localised zones, and the lack of communication between companies and agencies with data. Additionally, large variations in hydraulic properties have been noted over localised areas. This study sampled bores along a loosely east–west transect across urban Sydney, targeting the deeper Hawkesbury Sandstone and Narrabeen group aquifers. Very high salinities are recorded by several samples, interpreted to relate to the influence of the overlying Wianamatta Group and Cumberland Basin sediments in those locations. Equally however, this signal may record the impact of interaction with coal seams. Results also show inconsistencies between tritium and radiocarbon groundwater ‘ages’ in multiple locations, suggesting that extensive mixing occurs between aquifers. A relationship between bicarbonate, depth and δ 13C isotopic ratios highlights the influence of methanogenesis for deeper samples and either interaction with localised organic matter or deeper inputs derived from the coal measures. These findings have implications for potential coals seam gas extraction in the region, demonstrating that impacts could be significant in areas of high fracturing and connectivity. This supports previous assessments of groundwater vulnerability and the need for further detailed research. © Geological Society of Australia Inc
- ItemAnalysis of environmental isotopes in groundwater to understand the physical and chemical responses of a coastal aquifer to pumping.(International Association of Hydrogeologists, 2013-09-20) Currell, MJ; Cendón, DI; Cheng, XThe response of a multi-layered coastal aquifer in southeast Australia to decades of groundwater pumping, and the groundwater age, flow paths and salinisation processes were examined using isotopic tracer (δ18O, δ2H , δ13C, 3H and 14C). Groundwater radiocarbon (0.91 To 77.8 pMC) and tritium (below detection to O.23TU) contents decline with distance and depth away from basin margins; however, in the main zone of pumping, radiocarbon activities are generally homogeneous within a given depth horizon. A lack of tritium and low radiocarbon activities (<25 pMC) in groundwater in and around the pumping areas indicate that seasonal recovery of water levels (observed each year since c.1970) is related to capture of water with low tracer activities, rather than arrival of water recharged in modern times. Possible sources of water facilitating the seasonal recovery include release from storage in low permeability layers and/or horizontal transfer of water from more distant, undeveloped parts of the basin. Groundwater δ18O, δ2H and chloride contents indicate mixing between fresh meteoric water that is slightly depleted in stable isotopes relative to the local weighted mean, and marine water. On the basis of mixing calculations performed with Cl and δ18O, the most saline groundwater approximates an 80:20 mixture of fresh to oceanic water. Leakage of marine water into the Westernport Group sediments through an incised tidal channel, and dilution of this water by fresh groundwater released from other sources (e.g. aquitards or offshore sediments) can explain the observed Cl-δ180 values. Overall stability in seasonally recovered water levels and groundwater salinities over the past 3 decades indicate that the system has likely reached a state of dynamic equilibrium with respect to water balance and solute compositions, following a major change in the ow system and solute distributions that occurred in the early stages following development of the aquifer. Complex geological structure and variable degrees of flushing of saline water (largely controlled by proximity to recharge sources), result in heterogeneous groundwater salinities around the coastline.
- ItemAnalysis of environmental isotopes in groundwater to understand the response of vulnerable coastal aquifer to pumping: Western Port Basin, south-eastern Australia(Springer, 2013-11-01) Currell, MJ; Cendón, DI; Cheng, XThe response of a multi-layered coastal aquifer in southeast Australia to decades of groundwater pumping, and the groundwater age, flow paths and salinization processes were examined using isotopic tracers. Groundwater radiocarbon and tritium contents decline with distance and depth away from basin margins; however, in the main zone of pumping, radiocarbon activities are generally homogeneous within a given depth horizon. A lack of tritium and low radiocarbon activities (< 25 pMC) in groundwater in and around the pumping areas indicate that seasonal recovery of water levels is related to capture of old water with low radioisotope activities, rather than arrival of recently recharged water. Mechanisms facilitating seasonal recovery include release of water from low-permeability layers and horizontal transfer of water from undeveloped parts of the basin. Overall stability in seasonally recovered water levels and salinities for the past three decades indicate that the system has reached a dynamic equilibrium with respect to water balance and salinity, following a major change in flow paths and solute distributions after initial development. Groundwater delta O-18, delta H-2 and chloride contents indicate mixing between fresh meteoric-derived groundwater and marine water at the coast, with the most saline groundwater approximating an 80:20 mixture of fresh to oceanic water. © 2013, Springer.
- ItemAssessing connectivity between an overlying aquifer and a coal seam gas resource using methane isotopes, dissolved organic carbon and tritium(National Centre for Groundwater Research And Training, 2015-11-03) Iverach, CP; Cendón, DI; Hankin, SI; Lowry, D; Fisher, RE; France, JL; Nisbet, EG; Baker, AA; Kelly, BFJCoal seam gas (CSG) production can have an impact on groundwater quality and quantity in adjacent or overlying aquifers. To assess this impact we need to determine the background groundwater chemistry and to map geological pathways of hydraulic connectivity between aquifers. In south-east Queensland (Qld), Australia, a globally important CSG exploration and production province, we mapped hydraulic connectivity between the Walloon Coal Measures (WCM, the target formation for gas production) and the overlying Condamine River Alluvial Aquifer (CRAA), using groundwater methane (CH4) concentration and isotopic composition (δ13C-CH4), groundwater tritium (3H) and dissolved organic carbon (DOC) concentration. A continuous mobile CH4 survey adjacent to CSG developments was used to determine the source signature of CH4 derived from the WCM. Trends in groundwater δ13C-CH4 versus CH4 concentration, in association with DOC concentration and 3H analysis, identify locations where CH4 in the groundwater of the CRAA most likely originates from the WCM. The methodology is widely applicable in unconventional gas development regions worldwide for providing an early indicator of geological pathways of hydraulic connectivity. © The Authors.
- ItemAssessing connectivity between an overlying aquifer and a coal seam gas resource using methane isotopes, dissolved organic carbon and tritium(Nature, 2015-11-04) Iverach, CP; Cendón, DI; Hankin, SI; Lowry, D; Fisher, RE; France, JL; Nisbet, EG; Baker, AA; Kelly, BFJCoal seam gas (CSG) production can have an impact on groundwater quality and quantity in adjacent or overlying aquifers. To assess this impact we need to determine the background groundwater chemistry and to map geological pathways of hydraulic connectivity between aquifers. In south-east Queensland (Qld), Australia, a globally important CSG exploration and production province, we mapped hydraulic connectivity between the Walloon Coal Measures (WCM, the target formation for gas production) and the overlying Condamine River Alluvial Aquifer (CRAA), using groundwater methane (CH4) concentration and isotopic composition (δ13C-CH4), groundwater tritium (3H) and dissolved organic carbon (DOC) concentration. A continuous mobile CH4 survey adjacent to CSG developments was used to determine the source signature of CH4 derived from the WCM. Trends in groundwater δ13C-CH4 versus CH4 concentration, in association with DOC concentration and 3H analysis, identify locations where CH4 in the groundwater of the CRAA most likely originates from the WCM. The methodology is widely applicable in unconventional gas development regions worldwide for providing an early indicator of geological pathways of hydraulic connectivity. © The Authors. This work is licensed under a Creative Commons Attribution 4.0 International Licence. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons licence, users will need to obtain permission from the licence holder to reproduce the material.
- ItemAssessing the hydraulic connection between fresh water aquifers and unconventional gas production using methane and stable isotopes(European Geosciences Union, 2015-04-12) Iverach, CP; Cendón, DI; Hankin, SI; Lowry, D; Fisher, RE; France, JL; Nisbet, EG; Baker, AA; Kelly, BFJUnconventional gas developments pose a risk to groundwater quality and quantity in adjacent or overlying aquifers. To manage these risks there is a need to measure the background concentration of indicator groundwater chemicals and to map pathways of hydraulic connectivity between aquifers. This study presents methane (CH4) concentration and isotopic composition, dissolved organic carbon concentration ([DOC]) and tritium (3H) activity data from an area of expanding coal seam gas (CSG) exploration and production (Condamine Catchment, south-east Queensland, Australia). The target formation for gas production within the Condamine Catchment is the Walloon Coal Measures (WCM). This is a 700 m thick, low-rank CSG resource, which consists of numerous thin discontinuous lenses of coal separated by very fine-to medium-grained sandstone, siltstone, and mudstone, with minor calcareous sandstone, impure limestone and ironstone. The thickness of the coal makes up less than 10% of the total thickness of the unit. The WCM are overlain by sandstone formations, which form part of the Great Artesian Basin (GAB). The Condamine Alluvium fills a paleo-valley carved through the above formations. A combination of groundwater and degassing air samples were collected from irrigation bores and government groundwater monitoring boreholes. Degassing air samples were collected using an SKC 222-2301 air pump, which pumped the gas into 3 L Tedlar bags. The groundwater was analysed for 3H and [DOC]. A mobile CH4 survey was undertaken to continuously sample air in and around areas of agricultural and unconventional gas production. The isotopic signature of gas from the WCM was determined by sampling gas that was off-gassing from a co-produced water holding pond as it was the largest emission that could be directly linked to the WCM. This was used to determine the source signature of the CH4 from the WCM. We used Keeling plots to identify the source signature of the gas sampled. For the borehole samples these plots assume that there are only two sources of CH4, each with a unique isotopic signature. When the two sources mix in varying proportions they will plot along a straight line in the Keeling plot. Geometric mean displacement was used to fit a regression line and determine the intercept value. Within the Keeling plot, samples clustered according to their 3H and [DOC] values. One cluster is associated with near surface biological processes, while the other cluster can be attributed to gas sourced from the WCM. This indicates that in places there is hydraulic connectivity between the WCM and the overlying Condamine Alluvium. The results from this case study demonstrate that measuring 3H activity, [DOC] and CH4 concentrations in combination with CH4 isotopic analysis can provide an early indicator of hydraulic connectivity in areas of expanding unconventional gas development. © Author(s) 2015. CC Attribution 3.0 License.
- ItemAssessment 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, AA 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.
- ItemAssessment of multi-layered sandstone aquifers in the Sydney Basin, Blue Mountains(International Association of Hydrogeologists, 2010-10-31) Green, RT; Russell, G; Williams, M; Cendón, DIHydrogeological investigations of the Blue Mountains sandstone on the western fringe of the Sydney Basin have shown it to be a complex multi-layered sandstone aquifer. The shallow and intermediate aquifers are critical to spring flow and to stream baseflow in the upper plateau rivers. These aquifers will be typically the ones that support groundwater dependent ecosystems, such as wetlands and hanging swamps. The deep regional aquifer system appears to be flowing towards the deep incised valley rivers and across the Lapstone Monocline with some discharge likely into the Hawkesbury - Nepean River at the base of the plateau. The deep aquifer appears to have a large positive pressure head, which may indicate a significant proportion of the groundwater from the lower Blue Mountains is flowing under the Hawkesbury - Nepean River out further east to the coast. A regional monitoring bore network was first established in 1997 in the upper Blue Mountains near Katoomba. Over the next 10 years increased demand for groundwater saw entitlements approach the estimated extraction limit for this porous rock aquifer. Concurrently the World Heritage National Park and other nature conservation areas that surround the area have required specific water allocation. Further enhancement of the monitoring network was required in the lower Blue Mountains to manage the competing uses. This paper focuses on a series of additional monitoring bores installed in the lower Blue Mountains for sustainable groundwater management.
- ItemAssessment of radionuclide distributions at an Australian legacy radioactive waste site(South Pacific Radioactivity Association, 2010-09-01) Payne, TE; Cendón, DI; Collins, RN; Dore, M; Hankin, SI; Harrison, JJ; Hughes, CE; Johansen, MP; Thiruvoth, S; Twining, JR; Wilsher, KLDuring the 1960s, low level radioactive waste was buried in shallow trenches at a disposal site in south-eastern Australia, known as the Little Forest Burial Ground. This paper discusses preliminary findings of research into the distribution of radionuclides at the site, including soils, groundwater and biota. In particular, we are studying the mobility of radionuclides; and their uptake by plants, insects and small animals. Groundwater monitoring indicates that there has been limited movement of radioactivity, other than a tritium plume that extends at least 100 m. The tritium results are being used to define the groundwater flowpaths, and the effects of seasonal and climatic factors. The pattern of tritium distribution suggests that the source of tritium is predominantly within the waste materials. However, tritium derived from a nearby municipal landfill contributes to tritium concentrations in some groundwaters, with smaller amounts from cosmogenic tritium and atmospheric deposition originating from the nearby HIFAR reactor (shut down in 2007). The tritium data provide a record of water movement against which the relative mobility of other radionuclides can be assessed. There are measurable amounts of 60Co, 90Sr, 137Cs and traces of actinides in some soils, groundwater and vegetation samples taken in close proximity to the disposal area. Isotopic ratios such as δ13C, δ180, δ2H, δ34S and 87Sr/86Sr are being measured in groundwater, in addition to the radioactive isotopes originating from the disposed wastes. Synchrotron EXAFS and XANES studies are being applied to study elemental chemical environments and oxidation states in the soils at the site. We have recently undertaken a major geophysical investigation and drilling program; and installation of an improved array of water sampling boreholes is planned. Therefore, many more samples of groundwater and soils are becoming available for analysis.
- ItemAssessment of radionuclide movement at an Australian legacy radioactive waste site(EMSL, 2009-09-20) Payne, TE; Cendón, DI; Collins, RN; Hankin, SI; Harrison, JJ; Hughes, CE; Johansen, MP; Twining, JR; Waite, TDNot available
- ItemAssessment of the aquifers in the West Canning Basin-Pardoo - application of isotopic and hydrogeochemical techniques(Australian Nuclear Science and Technology Organisation, 2014-01) Meredith, KT; Cendón, DI; Hankin, SI; Peterson, MA; Hollins, SE
- ItemAustralian rainfall isotope variability and its relationship with groundwater(Copernicus Publications, 2017-07-10) Hughes, CE; Crawford, J; Cendón, DI; Meredith, KT; Hollins, SERainfall stable isotope composition varies dramatically across the Australian continent. Using monthly deuterium and oxygen-18 data from 15 Global Network of Isotopes in Precipitation (GNIP), sites the underlying causes for the spatial and temporal variability have been investigated. Because of the island nature of Australia, moisture originates from the Indian Ocean to the west and the Pacific Ocean to the east, and is dominated by the monsoon and tropical cyclones to the north and frontal and low pressure systems to the south. Simple rainfall amount or temperature relationships don’t explain what is observed over this low-elevation continent because of the huge spatial variability in moisture source and synoptic processes. However, latitude, elevation and continentality were found to have some influence on the isotopic average at the 15 sites. Using relationships developed with data from the 15 GNIP sites and additional data from higher elevation sites, an isoscape has been developed. This is used to investigate what drives groundwater recharge at a variety of locations across Australia. In many regions groundwater recharge can be linked isotopically to extreme high rainfall events such as tropical cyclones, east coast lows or major troughs which may occur on sub-annual or decadal time scales. For many inland sites, recharge from such events results from widespread flooding over hundreds or thousands of kilometers, introducing an evaporated signature to the groundwater, or one that reflects a different composition to local rainfall. In contrast, reliable seasonal rainfall from the monsoon in the north, or winter rainfall in the south west leads to groundwater signatures in alluvial, karst and fractured rock aquifers that reflect wet season averages. A better understanding of how these processes vary across the continent improves our ability to apply stable isotopes to trace groundwater recharge and ultimately provides valuable information for water resource managers to understand the sustainability of groundwater and connected surface water systems. © Author(s) 2017. CC Attribution 3.0 License.
- ItemBaselining lower Namoi groundwater and evaluating Pilliga CSG developments(University of New South Wales, 2018-12) Kelly, BFJ; Cendón, DI; Iverach, CPHydrochemical and isotopic results reveal that there are distinct differences in the groundwater chemistry with depth throughout the Lower Namoi Alluvium (LNA). This is due to varying recharge processes, as well as the evolution of the groundwater chemistry through the system. Na-HCO3 - type groundwater is dominant throughout the study area, increasing in concentration with depth. Locally, in areas where the alluvial sediments have a higher proportion of clay, the groundwater is more saline because of evapotranspiration processes and is classified as Na-Cl-type groundwater. Groundwater residence time (an indicator of age) is correlated with distance from the river channel for near surface samples, and with depth due to increased proportional input for the Great Artesian Basin (GAB). Where the groundwater is enriched in Na+, it is most likely the result of mixing between the Na+-rich GAB groundwater and surface-sourced water (river leakage, floodwater recharge, and areal recharge (including irrigation deep drainage)). The weathering of silicate minerals and cation exchange processes in the shallow alluvium with a higher clay content may also contribute to the enrichment of Na+ in the LNA. High activities of tritium (3H) in the shallow aquifer close to the river corridor highlight the importance of river leakage and flood associated recharge to total aquifer recharge. Modelling the mixing of various water types using a box model mixing approach shows that large floods are the biggest contributor to the renewal of the near-river shallow groundwater. Our calculations also show that minor recharge occurs into the shallow groundwater proximal to Namoi River in years when the region experiences average rainfall. Isotopic data (36Cl/Cl, 14C and 3H) indicate that the residence time of the groundwater is highly dependent on the proportion of groundwater sourced from surface recharge and input from the GAB in each location. The Lower Namoi alluvial groundwater in the study area is a mixture of groundwater of different origin mainly: a) a young component with residence times of < 70 years associated with periodic flooding and; b) groundwater that is potentially hundreds of thousands of years old, mostly derived from outflow from the GAB units. 6 Methane is ubiquitous throughout the alluvium, with the concentration increasing significantly with depth. The CH4 isotope data suggest that the CH4 in the LNA is biologically produced, with varying degrees of microbial oxidation occurring. Our results, coupled with CH4 data collected from formations underlying the GAB (primarily the Hokissons coal seam) by Eastern Star Gas (ESG 2008-2011) suggest that mixing of groundwater in the LNA with water from the GAB has influenced both the occurrence of CH4 in the alluvium (hence the increased concentration and lighter isotopic signature with depth), and the processes acting on the CH4 once it has reached the LNA. Microbial community analyses of the alluvial groundwater show 3 distinct changes in composition with depth. These changes with depth are related to the changing geochemical environment through the vertical profile of the LNA, because of multiple recharge inputs. There are significantly less methanogens in the groundwater than suggested by the CH4 concentration, indicating that in situ production is not the primary source of CH4 to the alluvium. Comprehensive details on the biogeochemical results from this project are published in: Iverach C.P; Cendón D.I.; Meredith K.T.; Wilcken K.M.; Hankin S.I.; Andersen M.S.; Kelly B.F.J, (2017) A multi-tracer approach to constraining artesian groundwater discharge into an alluvial aquifer, Hydrology and Earth System Sciences, vol. 21, pp. 5953 - 5969, http://dx.doi.org/10.5194/hess-21-5953-2017
- ItemThe benefits of a multidisciplinary team model for groundwater-surface water investigations, Thirlmere Lakes, NSW.(National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-25) Cowley, KL; Cohen, TJ; Forbes, MS; Barber, E; Allenby, J; Andersen, MS; Anibas, C; Glamore, W; Chen, SY; Johnson, F; Timms, W; David, K; McMillan, T; Cendón, DI; Peterson, MA; Hughes, CE; Krogh, MThe Thirlmere Lakes Research Program (TLRP) is a four-year collaborative multidisciplinary program designed to gain a whole-of-system understanding of the hydro-dynamics of a complex lake environment. The program was established from concerns that proximal aquifer interference activities were factors in recent lake level declines. Five research teams were established to investigate five adjacent lakes set within an entrenched meander bend located south-west of Sydney. The project involved lithological, geochemical and geochronological analysis from lake beds and surrounding slopes to understand lake evolution and determine potential past lake-drying events. Further geological understanding of the lake area was obtained from resistivity imaging (RI), ground penetrating radar (GPR), and analysis of rock cores that were drilled from two deep bores adjacent the lakes. Development of water balance budgets involved fine-scale on-site meteorological measurements including on-site evapotranspiration monitoring, combined with high-resolution bathymetry from RTK GPS, LiDAR surveying and drone photogrammetry. Groundwater-surface water interactions were measured using lake-bed multilevel temperature and pressure arrays, hydraulic head measurements and fine-scale isotope, major ion and environmental tracer time-series analysis. Preliminary findings indicate that the five lakes have been separated for over ~100,000 years and that the lakes themselves contain sediment that is possibly up to 250,000 years old. Assessing the modern dynamics we show that current lake level declines during a period of low rainfall are largely evaporation dominated. One lake however appears to have greater water storage in adjacent sediments providing compensatory inflows. In a second lake, there are indications of localised connectivity with shallow (≤18m) groundwater, but no evidence of connectivity with deeper aquifers. Geological surveys indicate a clay layer 6-8 m below the lakes and spatial variations in both sediment and rock geology. The influence of these geological features, including structures projecting towards the lakes, on groundwater storage and flow is the focus of ongoing research as is temporal variability and lake interactions at different lake levels. The benefits of the multidisciplinary team model include refining the research targeting areas of uncertainty and to enhance and calibrate each team’s results. This approach will provide a comprehensive whole-of-system model of the evolution and hydro-dynamics of a complex lake system. © The Authors
- ItemBiogeochemical constraints on the origin of methane in an alluvial aquifer: evidence for the upward migration of methane from underlying coal measures(European Geosciences Union, 2017-04-26) Iverach, CP; Beckmann, S; Cendón, DI; Manefield, M; Kelly, BFJGeochemical and microbiological indicators of methane (CH4) production, oxidation and migration processes in groundwater are important to understand when attributing sources of gas. The processes controlling the natural occurrence of CH4 in groundwater must be characterised, especially when considering the potential impacts of the global expansion of unconventional gas production on groundwater quality and quantity. We use geochemical and microbiological data, along with measurements of CH4 isotopic composition ( 13C-CH4), to determine the processes acting upon CH4 in a freshwater alluvial aquifer that directly overlies coal measures targeted for unconventional gas production in Australia. A combination of geochemical and microbiological groundwater samples were collected from private irrigation boreholes. The groundwater was analysed for the major ions, water stable isotopes ( 2H and 18O), the isotopic composition of dissolved organic carbon ( 13CDOC) and dissolved inorganic carbon ( 13CDIC). Quantitative realtime PCR was used to determine abundances of bacterial and archaeal 16S rRNA gene targets and functional gene targets in the groundwater. Measurements of CH4 indicate that there is biogenic CH4 in the aquifer, however microbial community analysis indicates that there are no methanogenic archaea in the groundwater. In addition, geochemical data, particularly the isotopes of DIC and, as well as the concentration of SO2-4 , indicate limited potential for methanogenesis insitu. Microbial community analysis also showed that aerobic oxidation of CH4 is occurring in the alluvial aquifer despite the absence of a microbial pathway to produce the CH4. The combination of microbiological and geochemical indicators suggests that the most likely source of CH4, where it was present in the freshwater aquifer, is the upward migration of CH4 from the underlying coal measures. © Author(s) 2016. CC Attribution 3.0 License.