Browsing by Author "Currell, MJ"

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    Analysis 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, X
    The 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.
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    Analysis 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, X
    The 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.
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    Combining environmental isotopes with contaminants of emerging concern (CECs) to characterise wastewater derived impacts on groundwater quality
    (Elsevier B.V., 2020-09-01) McCance, WG; Jones, OAH; Cendón, DI; Edwards, M; Surapaneni, A; Chadalavada, S; Wang, S; Currell, MJ
    The potential for Wastewater Treatment Plants (WWTPs) to cause adverse impacts to groundwater quality is a major global environmental challenge. Robust and sensitive techniques are required to characterise these impacts, particularly in settings with multiple potential contaminant sources (e.g. agricultural vs. site-derived). Stable (δ2HH2O, δ18OH2O, δ15NNO3, δ18ONO3 and δ13CDIC) and radioactive (3H and 14C) isotopes were used in conjunction with three Contaminants of Emerging Concern (CECs) - carbamazepine, simazine and sulfamethoxazole - to discriminate between multiple potential contamination sources at an Australian WWTP. The radioactive isotope tritium provided a sensitive indicator of recent (post-1990s) leakage, with groundwater activities between 0.68 and 1.83 TU, suggesting WWTP infrastructure (activities between 1.65 and 2.41) acted as a recharge ‘window’, inputting treated or partially treated effluent to the underlying groundwater system. This was corroborated by water stable isotopes, which showed clear demarcation between δ18OH2O and δ2HH2O in background groundwater (δ18OH2O and δ2HH2O values of approximately −5 and −28‰, respectively) and those associated with on-site wastewater (median δ18OH2O and δ2HH2O values of −1.2 and −7.6‰, respectively), with groundwater down-gradient of the plant plotting on a mixing line between these values. The CECs, particularly the carbamazepine:simazine ratio, provided a means to further distinguish wastewater impacts from other sources, with groundwater down-gradient of the plant reporting elevated ratios (median of 0.98) compared to those up-gradient (median of 0.11). Distinctive CEC ratios in impacted groundwater close to the WWTP (∼3.0) and further down-gradient (2.7–9.3) are interpreted to represent a change in composition over time (i.e., recent vs. legacy contamination), consistent with the site development timeline and possible changes in effluent composition resulting from infrastructure upgrades over time. The data indicate a complex set of co-mingled plumes, reflecting different inputs (in terms of both quantity and concentration) over time. Our approach provides a means to better characterise the nature and timing of wastewater derived impacts on groundwater systems, with significant global implications for site management, potentially allowing more targeted monitoring, management and remedial actions to be undertaken. © 2020 Elsevier B.V.
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    Decoupling wastewater impacts from hydrogeochemical trends in impacted groundwater resources
    (Elsevier B. V., 2021-06-20) McCance, WG; Jones, OAH; Cendón, DI; Edwards, M; Surapaneni, A; Chadalavada, S; Currell, MJ
    In the urban environment, anthropogenic activities provide numerous potential sources of contamination, which can often lead to difficulties in identifying the processes impacting groundwater quality (natural and anthropogenic). This is particularly relevant at Wastewater Treatment Plants (WWTPs) that are often subject to changes in land use and composition of contaminant sources over time and space, as well as multiple potential hydrogeochemical interactions. To help address this issue, we demonstrate how long-term time-series analysis of major ions and key contaminants of concern, which are routinely collected by WWTP operators, can be analysed using hydrogeochemical plotting tools, multivariate statistics and targeted isotopic analysis, to provide a means of better characterising key hydrogeochemical influences and anthropogenic inputs. Application of this approach to a WWTP in south-eastern Australia indicated that anthropogenic impacts were the primary driver influencing the local hydrogeochemical environment and groundwater quality. However, secondary processes, including mineral (particularly calcite) dissolution, ion exchange and possible dedolomitisation, as well as natural degradation/transformation of contaminants were also important. Long-term, time-series analysis of trends in NO3-N, NH4-N, Ca2+, SO42−, HCO3− and K+ in conjunction with the other lines of evidence, allowed for enhanced separation between individual contaminant sources, particularly when paired with a detailed site history and Conceptual Site Model (CSM). This indicated that off-site agricultural impacts post-date most site derived impacts, and to date, have not significantly added to the identified contaminant plume. The outcomes of this work have significant global application in the identification, assessment, and control of environmental and health risks at complex sites and show how significant value (rarely obtained) can be derived from the analysis of routine monitoring datasets, particularly when analysed using a multiple lines of evidence approach. © 2021 Elsevier B.V.
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    Environmental isotopes as indicators of groundwater recharge, residence times and salinity in a coastal urban redevelopment precinct in Australia
    (Springer Nature Limited, 2019-12-04) Hepburn, E; Cendón, DI; Bekele, D; Currell, MJ
    Fishermans Bend is an urban redevelopment precinct situated on the Yarra River estuary in Melbourne, Australia. Understanding the hydrogeological system is important for characterising the impacts from legacy contamination and for monitoring the effects of urbanisation on groundwater flow systems and quality. Stable isotopes of water (δ18O, δ2H) and carbon (δ13C), radioisotopes (3H, 14C) and other geochemical indicators were used to assess sources of water and salinity in the shallow groundwater. Groundwater in the upper aquifer was predominantly Ca-HCO3− dominant, with fresh to brackish salinity—189–3,680 mg/L total dissolved solids (TDS). Localised areas of Ca-SO42− and Na-HCO3− dominant groundwater were impacted by industrial activities and legacy landfills, respectively. Stable isotopes (e.g. δ18O −5.7 to −2.9‰) and tritium activities (1.75–2.45 TU) within the aquifer indicate meteoric water recharged by modern rainfall with short residence times. Carbonate dissolution from shell material, and decay of organic waste and methanogenesis in landfill-leachate-impacted bores were shown to enrich δ13C values up to −4.2‰. In contrast, groundwater in the adjacent/lower aquitard was Na-Cl dominant and saline (19,600–23,900 mg/L TDS), with molar ratios reflective of ocean water, indicating relict emplaced salts. This is consistent with 14C dating of shell material, indicating deposition in a Holocene marine environment. The presence of tritium above background levels (0.20–0.35 TU) in the groundwater, however, suggests a component of modern recharge. Salinity fluctuations within the aquitard at times of peak river level suggest the modern water source is ingress from the adjacent Yarra River. © 2021 Springer Nature Switzerland AG.
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    Erratum: Analysis of environmental isotopes in groundwater to understand the response of a vulnerable coastal aquifer to pumping: Western Port Basin, south-eastern Australia
    (Springer Nature, 2013-09-19) Currell, MJ; Cendón, DI; Cheng, X
    A monitoring well, bore ID 71856, is indicated as being screened in the Sherwood formation in Tables 1 and 2; in fact it is screened within the Older Volcanics unit. This error was noticed after the proofs were approved for publication. © 2013, Springer.
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    Evaluación de aspectos hidrodinámicos, geoquímicos y aptitudes de uso de capas acuíferas confinadas en la planicie loéssica de Marcos Juárez
    (National Atomic Energy Commission CNEA, 2020-11-23) Giacobone, D; Blarasin, MT; Matteoda, EM; Lutri, V; Cabrera, A; Currell, MJ; Cendón, DI; Cabrera, AE
    Los sistemas acuíferos confinados (SAC) son utilizados para diferentes actividades en la provincia de Córdoba. Dado que la tasa de renovación de estos sistemas puede superar los miles de años, es necesario su estudio y manejo sustentable. El objetivo de este trabajo fue evaluar los aspectos hidrodinámicos, geoquímicos y de aptitudes de uso asociados a los SAC de la planicie loéssica de Marcos Juárez, relacionándolos con el modelo hidrogeológico propuesto para la provincia. Los resultados indican que estas capas, situadas entre los 100 y 150 m de profundidad, se pueden asignar al sistema acuífero confinado SAC B definido para el centro-Este de Córdoba. El flujo regional del agua en estas capas profundas ocurre en la planicie cordobesa en grandes escalas de tiempo, en el orden de 20.000 a 30.000 años AP (edad radiocarbono) observándose descarga parcial en la depresión tectónica de San Antonio. Desde el punto de vista hidráulico, se identificaron dos zonas, la planicie loéssica con perforaciones de tipo semisurgente y la depresión tectónica San Antonio con características de artesianismo, siendo las perforaciones surgentes. El sistema de flujo condiciona el aumento gradual del contenido salino del agua, resultando ésta salobre, con CE desde 3060 a 5500 μS/cm, y de tipo clorurada-sulfatada, sulfatada-clorurada, sulfatada y clorurada con catión dominante sodio. Los procesos geoquímicos más importantes interpretados en este sistema acuífero confinado son el intercambio catiónico, que libera Na+ al agua, la disolución/precipitación de sales de carbonato/sulfatos presentes en los sedimentos y el aumento de cloruros, fundamentalmente aportado por la fase atmosférica, en el sentido de flujo subterráneo. El principal uso de los SAC B en la planicie loéssica de Marcos Juárez es ganadero, y los resultados indican que es apto para bovinos de cría, tambo e inverne, aunque en algunas ocasiones la concentración de sulfato es elevada para dicha actividad.
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    Evaluación hidrogeológica e isotópica de capas acuíferas y su relación con presencia de atrazina en la Planicie Loésica de Córdoba. Argentina
    (International Congress of Agroecology, 2020-11-25) Giacobone, D; Blarasin, MT; Lutri, V; Cabrera, A; Cendón, DI; Currell, MJ; Cabrera, AE; Matteoda, EM; Aparicio, VC
    The presence of contaminants in groundwater is matter of concern due to the aquifers constitute the major reserve of liquid fresh water of the world. The objective of this work was to assess the presence of atrazine in the unconfined aquifer and confined aquifer layers of the Marcos Juarez loessic plain linking with the regional hydrogeological model. For this purpose, radiocarbon ages (pMC) and stable water isotopes (δ2H y δ18O) were also evaluated. It is concluded that there are evidences of the impact of agricultural activities on both aquifers, being higher on the unconfined aquifer that receives modern water recharge.
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    Geochemical indicators of the origins and evolution of methane in groundwater: Gippsland Basin, Australia
    (Springer, 2016-08-06) Currell, MJ; Banfield, D; Cartwright, I; Cendón, DI
    Recent expansion of shale and coal seam gas production worldwide has increased the need for geochemical studies in aquifers near gas deposits, to determine processes impacting groundwater quality and better understand the origins and behavior of dissolved hydrocarbons. We determined dissolved methane concentrations (n = 36) and δ 13C and δ 2H values (n = 31) in methane and groundwater from the 46,000-km 2 Gippsland Basin in southeast Australia. The basin contains important water supply aquifers and is a potential target for future unconventional gas development. Dissolved methane concentrations ranged from 0.0035 to 30 mg/L (median = 8.3 mg/L) and were significantly higher in the deep Lower Tertiary Aquifer (median = 19 mg/L) than the shallower Upper Tertiary Aquifer (median = 3.45 mg/L). Groundwater δ 13C DIC values ranged from -26.4 to -0.4 ‰ and were generally higher in groundwater with high methane concentrations (mean δ 13C DIC = -9.5 ‰ for samples with >3 mg/L CH 4 vs. -16.2 ‰ in all others), which is consistent with bacterial methanogenesis. Methane had δ 13C CH4 values of -97.5 to -31.8 ‰ and δ 2H CH4 values of -391 to -204 ‰ that were also consistent with bacterial methane, excluding one site with δ 13C CH4 values of -31.8 to -37.9 ‰, where methane may have been thermogenic. Methane from different regions and aquifers had distinctive stable isotope values, indicating differences in the substrate and/or methanogenesis mechanism. Methane in the Upper Tertiary Aquifer in Central Gippsland had lower δ 13C CH4 (-83.7 to -97.5 ‰) and δ 2H CH4 (-236 to -391 ‰) values than in the deeper Lower Tertiary Aquifer (δ 13C CH4 = -45.8 to -66.2 ‰ and δ 2H CH4 = -204 to -311 ‰). The particularly low δ 13C CH4 values in the former group may indicate methanogenesis at least partly through carbonate reduction. In deeper groundwater, isotopic values were more consistent with acetate fermentation. Not all methane at a given depth and location is interpreted as being necessarily produced in situ. We propose that high dissolved sulphate concentrations in combination with high methane concentrations can indicate gas resulting from contamination and/or rapid migration as opposed to in situ bacterial production or long-term migration. Isotopes of methane and dissolved inorganic carbon (DIC) serve as further lines of evidence to distinguish methane sources. The study demonstrates the value of isotopic characterisation of groundwater including dissolved gases in basins containing hydrocarbons. Copyright © 2016, Springer Nature
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    Groundwater in southeast Australia: links to recharge variations and past climates
    (International Association of Hydrogeologists, 2013-01-20) Cendón, DI; Meredith, KT; Hughes, CE; Hollins, SE; Currell, MJ; Markowska, M
    Palaeogroundwater from many locations around the world contains water stable isotope trends that are linked to climatic and therefore recharge variations through the last ~30 ka. Some examples are the variations observed in the Sahara-Sahel region where humidity sources can be differentiated (Edmunds et al. 2004) and or the markedly depleted values associated with glacial activity in many basins of northern part of Europe and America (Baidla et al. 2009). ln Australia with the lack of extensive glaciation, it is anticipated that water stable isotope trends do not show major variations through time. However, in the South East of Australia, particularly in the Sydney Basin (NSW) and also across the continent in the Perth Basin (WA), deuterium excess (d-excess) show high values with an average of 15%o (n=135) in the case of the Sydney Basin. The high values are not only found in modern precipitation and groundwater but also in groundwater with residence times exceeding 20 ka for the Sydney Basin. Water stable isotopes from several locations around the Sydney Basin are presented showing regional variations and localised changes due to orography. The chronological framework is determined from 14C DlC in the same groundwater samples. The dominant siliciclastic nature of most of the aquifers in the region minimises major 14C dilution and the combination of general hydrogeochemistry and 87Sr/86Sr results are used to constrain processes such as the dissolution of dispersed carbonates when estimating groundwater residence times. These records will be, where possible, compared to higher resolution records such as pollen, where parallelisms and differences will be discussed.
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    Hydrogeological and isotopic evaluation of aquifer layers and their relation with atrazine presence
    (Inés Gazzano Santos, Fabio Kessler Dal Soglio, Santiago Sarandón, 2022-08-11) Giacobone, DB; Blarasin, MT; Lutri, V; Matteoda, EM; Cabrera, A; Cendón, DI; Currell, MJ; Cabrera, AE; Aparicio, VC
    Dado que las aguas subterráneas constituyen la mayor reserva de agua dulce líquida en el mundo, la presencia de diversos contaminantes en acuíferos es un tema alarmante. En los sectores rurales prevalecen las problemáticas relacionadas con la contaminación del agua por la implementación de las prácticas de la agricultura industrializada. Con relación a uso de plaguicidas, la atrazina se aplica en forma extensiva en el cultivo de maíz y de sorgo para el control de malezas. El objetivo de este trabajo fue evaluar su presencia en el acuífero libre y las capas acuíferas confinadas de la planicie loéssica de Marcos Juárez, relacionándola con el modelo hidrogeológico de la región. Para tal fin, también se evaluó el comportamiento hidrogeológico con apoyo de isótopos estables del agua (δ2H y δ18O) y edades radiocarbono (pCM). Se concluye que hay evidencias del impacto de las prácticas agrícolas actuales en capas acuíferas confinadas, aunque es mayor en el acuífero libre por su mayor posibilidad de recibir recarga de aguas modernas y de vincularse a las actividades humanas. © Universidad de la República, Facultad de Agronomía 2022. The presence of diverse contaminants in groundwater is a matter of concern since the aquifers constitute the major reserve of liquid freshwater of the world. In rural environments issues related to groundwater contamination prevail by the implementation of industrialized agricultural practices. In relation to pesticide uses, atrazine is applied extensively in corn and sorghum crops to control weeds. The objective of this work was to assess the presence of atrazine in the unconfined aquifer and confined aquifer layers located in the Marcos Juarez loessic plain, linking it with the regional hydrogeological model. For this purpose, the hydrological behavior by stable water isotopes (δ2H and δ18O) and radiocarbon ages (pMC) was also evaluated. It is concluded that there are pieces of evidences of the impact of the current agricultural activities on both aquifers, being higher on the unconfined aquifer, that receives modern water recharge and is more linked to human activities. © Universidad de la República, Facultad de Agronomía 2022. CC-BY
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    Improving conceptual models of groundwater flow, recharge and quality evolution in a vulnerable coastal aquifer subject to rapid land/use change
    (International Association of Hydrogeologists in Canada, 2012-09-16) Currell, MJ; Cendón, DI
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    Intensive agriculture, a pesticide pathway to >100 m deep groundwater below dryland agriculture, Cordoba Pampas, Argentina
    (Elsevier BV, 2024-11) Cabrera, A; Cendón, DI; Aparicio, VC; Currell, MJ
    Groundwater pesticide pollution in shallow groundwater is a well-established global phenomenon. However, deep aquifers are widely thought to be naturally protected from such modern contaminants, by confining geological barriers and upwards hydraulic gradients. Here we document pervasive pesticide pollution in >100 m deep artesian wells in a sedimentary aquifer below dryland agriculture. The vertical distribution of key groundwater markers, including numbers and concentrations of pesticides, stable (δ18O & δ2H) and radioactive (3H & 14C) isotopes and ion concentrations were used to develop a conceptual model of pollutant transport to deep groundwater. Tritium, stable isotope and pesticide distributions in unconfined groundwater indicate that water table rise to <1 m below the surface (due to anthropogenic landscape modification and periodic flooding), has created a rapid pollutant ‘doorway’ to groundwater. Despite a lack of deep borehole pumping for irrigation, these rising water tables have permanently inverted previously upward hydraulic gradients towards the underlying semi-confined aquifer in some areas. Physical heterogeneities and/or leaky domestic boreholes then act as preferential transport avenues for surface pollutants to both unconfined and semi-confined groundwater. These pathways allow small aliquots of highly contaminated surface water and modern unconfined groundwater to mix with the pre-existing pre-modern deep groundwater, resulting in mixed isotopic signatures in deep wells (e.g., radiocarbon <5 pMC but detectable tritium) and detections of multiple synthetic pesticides in the deep aquifer, including AMPA at concentrations up to 4.93 µg/L and Metolachlor up to 0.015 µg/L. Our results demonstrate how semi-confined deep groundwaters may be contaminated by current agricultural techniques even where deep groundwater exploitation is limited. We urge measures to eliminate these pollutant pathways. © 2024 The Authors. Published by Elsevier B.V. Open Access.
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    Investigating the origin of salinity and aquifier interaction in a sesonally pumped confined aquifier system in southeast Australia (Western Port Basin)
    (Geological Society of Australia, 2014-07-07) Lee, S; Currell, MJ; Cendón, DI
    This ongoing study aims to identify the different sources of fresh/saline water, pathways, mechanisms of groundwater salinisation, and factors controlling salt-water intrusion in the Western Port Basin aquifer (Victoria, Australia). The multi-layered aquifer is characterised by variable distributions of fresh and saline groundwater at the coastline, which are speculated to result due to geological heterogeneity, and the influence of past sea levels. The spatial salinity distribution observed indicates that the typical situation of a dense saltwater wedge underlying fresh groundwater does not apply. Further to natural drivers, an understanding of the potential short and long term effects of seasonal pumping for irrigation in the basin is desired, particularly whether it induces migration of water from other areas in the basin or causes leakage from low-permeability horizons. The impact of seasonal pumping on the variation and distribution of salinity was examined at a nested bore site 500 m from the coast. Analyses of chloride concentration and δ18O in groundwater indicate various degrees of mixing between seawater and fresh meteoric groundwater. Multi-depth sampling in the upper aquifer, identified high salinity water with ~19% seawater mixture above slightly less saline water – with ~17% seawater; while samples from the lower aquifer yielded significantly fresher groundwater (~4 to 7% seawater). This is likely to be due to the relatively good connection between the upper aquifer and the ocean, and low-permeability material separating the shallow and deeper aquifers. Seasonal salinity changes were observed as a response to pumping, with salinity in the upper aquifer decreased by ~15.5% at the onset of pumping, and salinisation gradually increased once pumping ceased by ~22%. Recent 14C dating of groundwater in the proximity of the pumping area revealed low radiocarbon activities (<25 pMC) and a lack of tritium, which rules out the possibility of modern recharge reaching the pumping area. A thick Holocene clay cap (ranging from 10 to 30 m) covering significant areas and extending beneath the bay, limits rainfall recharge to the basin margins where the aquifers outcrop. Beneath the shallow bay a paleoriver channel incised deep into the bay floor sediments expose the aquifer to potential vertical and horizontal input from modern seawater. However, the lack of long-term salinisation despite decades of pumping, and the relatively old groundwater ages, imply buffering against saline intrusion by stores of relict fresh water. Incorporation of these results into a conceptual model will contribute to an improved understanding of the groundwater flow system and the long-term implications of pumping on future groundwater sustainability in the Western Port Basin.
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    Marine water from mid-holocene sea level highstand trapped in a coastal aquifer: Evidence from groundwater isotopes, and environmental significance
    (Elsevier, 2016-02-15) Lee, S; Currell, MJ; Cendón, DI
    A multi-layered coastal aquifer in southeast Australia was assessed using environmental isotopes, to identify the origins of salinity and its links to palaeo-environmental setting. Spatial distribution of groundwater salinity (electrical conductivity values ranging from 0.395 to 56.1 mS/cm) was examined along the coastline along with geological, isotopic and chemical data. This allowed assessment of different salinity sources and emplacement mechanisms. Molar chloride/bromide ratios range from 619 to 1070 (621 to 705 in samples with EC > 15 mS/cm), indicating salts are predominantly marine. Two distinct vertical salinity profiles were observed, one with increasing salinity with depth and another with saline shallow water overlying fresh groundwater. The saline shallow groundwater (EC = 45.4 to 55.7 mS/cm) has somewhat marine-like stable isotope ratios (δ18O = − 2.4 to − 1.9 ‰) and radiocarbon activities indicative of middle Holocene emplacement (47.4 to 60.4 pMC). This overlies fresher groundwater with late Pleistocene radiocarbon ages and meteoric stable isotopes (δ18O = − 5.5 to − 4.6‰). The configuration suggests surface inundation of the upper sediments by marine water during the mid-Holocene (c. 2–8 kyr BP), when sea level was 1–2 m above today's level. Profiles of chloride, stable isotopes, and radiocarbon indicate mixing between this pre-modern marine water and fresh meteoric groundwater to varying degrees around the coastline. Mixing calculations using chloride and stable isotopes show that in addition to fresh-marine water mixing, some salinity is derived from transpiration by halophytic vegetation (e.g. mangroves). The δ13C ratios in saline water (− 17.6 to − 18.4‰) also have vegetation/organic matter signatures, consistent with emplacement by surface inundation and extensive interaction between vegetation and recharging groundwater. Saline shallow groundwater is preserved only in areas where low permeability sediments have slowed subsequent downwards propagation. The configuration is unlikely to be stable long-term due to fluid density; this may be exacerbated by pumping the underlying aquifer. © 2015, Elsevier B.V.
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    Multiple isotope tracers reveal the sources of water sustaining ecologically and culturally significant springs, and their vulnerability to mining development
    (Elsevier, 2024-12) Campbell, AG; Cartwright, I; Cendón, DI; Currell, MJ
    The development of Australia’s largest approved coal mine in the Galilee Basin of northeast Australia will dramatically alter the region’s water resources. The Carmichael Coal Mine is located within eight kilometres of the Doongmabulla Springs Complex, which support endemic flora and fauna and hold crucial cultural significance to the Wangan and Jagalingou Traditional Owners. Uncertainties regarding the source(s) of water to the springs have so far prevented a clear understanding of how mining will affect their long-term health and hydrology. Environmental tracers (including 3H, 14C, 36Cl, 2H, 18O, 13C and 87Sr/86Sr) from 8 springs and 15 surrounding water bores, indicate that multiple sources of water, with vastly different residence times, sustain the Doongmabulla springs. R36Cl (79.1–80.8 x10-15), a14C (47.2–91.1 pMC) and the presence of 3H (up to 0.28 TU) suggest that relatively young water recharged during the Holocene and Late Pleistocene sustains three eastern springs close to the Carmichael mine. Significant R36Cl decay (to between 19.46 x10-15 and 56.94 x10-15) indicates that much older water from the Early-Mid Pleistocene (residence time > 500 ka) sustains springs in the west of the complex, alongside intermediate-aged water fractions (a14C 0.99–––95.73 pMC) and minor modern components (3H up to 0.518 TU). Regional groundwater flow in the Clematis Sandstone (sampled R36Cl values: 22.92 x10-15 ––109.9 x10-15) is likely the predominant source of very old water in the western springs, although contribution from deeper aquifers (e.g., Dunda Beds or Permian coal measures) cannot be ruled out. Aquifer geometry and hydraulic gradients suggest local-scale flow paths in the Clematis Sandstone and Dunda Beds are the likely source of Holocene water that is critical to the eastern springs. The revised understanding of the sources of groundwater implies that both the western and eastern springs are more vulnerable to mining impacts than has been previously assumed. Protection of ecologically and culturally significant springs worldwide from drawdown associated with resource extraction requires robust methods to characterise their water sources and this study presents a multi-isotope tracer approach that may be widely applicable. © 2024 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ ).
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    A review of radioactive isotopes and other residence time tracers in understanding groundwater recharge: Possibilities, challenges, and limitations
    (Elsevier B. V., 2017-12) Cartwright, I; Cendón, DI; Currell, MJ; Meredith, KT
    Documenting the location and magnitude of groundwater recharge is critical for understanding groundwater flow systems. Radioactive tracers, notably 14C, 3H, 36Cl, and the noble gases, together with other tracers whose concentrations vary over time, such as the chlorofluorocarbons or sulfur hexafluoride, are commonly used to estimate recharge rates. This review discusses some of the advantages and problems of using these tracers to estimate recharge rates. The suite of tracers allows recharge to be estimated over timescales ranging from a few years to several hundred thousand years, which allows both the long-term and modern behaviour of groundwater systems to be documented. All tracers record mean residence times and mean recharge rates rather than a specific age and date of recharge. The timescale over which recharge rates are averaged increases with the mean residence time. This is an advantage in providing representative recharge rates but presents a problem in comparing recharge rates derived from these tracers with those from other techniques, such as water table fluctuations or lysimeters. In addition to issues relating to the sampling and interpretation of specific tracers, macroscopic dispersion and mixing in groundwater flow systems limit how precisely groundwater residence times and recharge rates may be estimated. Additionally, many recharge studies have utilised existing infrastructure that may not be ideal for this purpose (e.g., wells with long screens that sample groundwater several kilometres from the recharge area). Ideal recharge studies would collect sufficient information to optimise the use of specific tracers and minimise the problems of mixing and dispersion. © 2017 Elsevier B.V
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    A review of the use of radiocarbon to estimate groundwater residence times in semi-arid and arid areas
    (Elsevier, 2020-01) Cartwright, I; Currell, MJ; Cendón, DI; Meredith, KT
    Groundwater is an important resource in arid and semi-arid regions and determining its residence times is critical for sustainable use. Radiocarbon (14C) is currently the primary geochemical tracer for determining residence times of regional groundwater systems. The analysis of 14C contents of dissolved inorganic carbon (DIC) became more straightforward following the development of accelerator mass spectrometry, which has led to an increase in the number of studies using 14C. However, the interpretation of 14C data is not always straightforward and many studies consider relatively few of the multiple processes that may affect the 14C contents of DIC in groundwater. Commonly, studies have focussed on correcting 14C contents for closed-system dissolution of 14C-free calcite, which is a near-ubiquitous process. However, especially in semi-arid and arid areas, uncertainties in the initial 14C contents and δ13C values of recharge due to the presence of low-14C soil CO2 in the deep unsaturated zone, recharge by rivers, or open-system calcite dissolution pose problems for mass balance calculations. Additionally, processes such as methanogenesis and mineralisation of organic carbon may be locally important. Most studies also assume a constant atmospheric 14C content and non-dispersive piston flow in aquifers, which results in residence times being underestimated and makes it difficult to compare the groundwater archive to other palaeoclimate or palaeoenvironment records. Additionally, mixing of water within aquifers, diffusion of 14C between low and high permeability layers, and sampling from multiple units in long-screen wells may limit whether a meaningful residence time can be determined. Overall, while it is relatively straightforward to estimate broad ranges of residence times or determine general patterns of groundwater flow, the quest to quantify residence times, flow rates, and recharge remains a challenge. The use of multiple radioactive tracers, better characterisation of δ13C values and 14C contents of the potential sources of DIC, and more critical assessment of flow systems will improve the utilisation of this important tracer. © 2019 Elsevier B.V
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    Stable isotopes as indicators of dissolved methane sources and cycling in the Gippsland Basin, Victoria
    (National Centre for Groundwater Research And Training, 2017-07-12) Currell, MJ; Cendón, DI; Cartwright, I
    A suite of environmental tracers were analysed from the Gippsland Basin, Victoria, to determine the origins of methane in groundwater and characterise the biogeochemical and physical processes controlling its occurrence and cycling. Water samples were collected from a range of depths and lithology, and were analysed for stable isotopes of methane plus a suite of other tracers - radiocarbon, noble gases (He-4, Ne, Ar), δ18O, δ2H and δ13CDIC. The data were analysed within the hydrogeological framework to characterise sources of methane in groundwater and identify possible transport processes. Methane isotopic compositions ranged widely throughout the system. Two predominant groups of methane were found, both of which were of bacterial origin. One group contained isotopes with typical acetate-fermentation signatures (δ13CCH4 = −45.8 to −66.2‰ and δ2HCH4 = −204 to −311‰), and largely occurred in deep groundwater, near the coast. The other group exhibited unusually depleted δ13CCH4 values by typical global standards (−83.7 to −97.5 ‰) and δ2HCH4 values between −236 and −391‰. This group is associated with relatively shallow groundwater, near areas of extensive lignite. Radiocarbon and He-4 data indicate that groundwater age increases with depth, however inter-aquifer mixing complicates age interpretations. Stable isotopes of water in the deepest parts of the system show relatively depleted δ18O and δ2H, suggesting isotopic modification during methanogenesis and/or depleted signatures associated with palaeo-recharge conditions. The study provides the first data on dual-isotopic compositions of methane in the Gippsland Basin, and new insights into sources and cycling of methane in a multi-layered sedimentary basin. The basin is one in which extensive groundwater extraction and mining activity occurs, which may be having ongoing effects on inter-aquifer connectivity for both water and gases.
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    Use of stable and radiogenic isotopes in characterising wastewater derived impacts in Urban and Peri-Urban areas
    (National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-24) McCance, WG; Jones, OAH; Edwards, M; Surapaneni, A; Chadalavada, S; Cendón, DI; Currell, MJ
    Objectives: This study focuses on one of South East Water’s Water Recycling Plants (WRPs), located adjacent to an area of significant agricultural activity (market gardens), where multiple potential sources of groundwater contamination (nutrients) have been identified. The primary objective was to examine the use of stable and radiogenic isotopes in conjunction with contaminants of emerging concern (e.g. pharmaceuticals) to gain a greater understanding of the underlying hydrogeochemical processes and separate wastewater-derived contamination from other potential sources e.g., agriculture. Design and methodology: This project combined long term groundwater monitoring data (collected since 1997) with in-situ isotopic tracers sampled in 2018-2019 including: δ2HH2O and δ18OH2O, δ13CDIC, 3H and 14C, analysed at ANTSO’s Lucas Heights facility, and δ18ONO3 and δ15NNO3, analysed at China’s Key Laboratory of Agricultural Water Resources. The isotopic data were combined with other lines of evidence, including contaminants of emerging concern (e.g. pharmaceuticals) analysed at RMIT, as an additional metric to better delineate wastewater impacts in a mixed source environment. Original data and results: Groundwater residence time indicators from groundwater wells located adjacent to or upgradient of the treatment plant, contain 14C and 3H activities (>73 pMC and >0.68 TU) which indicate a large component of modern recharge (i.e. <50 years old). Groundwater near suspected leaky infrastructure contains elevated levels of these radiogenic isotopes compared to those considered more indicative of background conditions (>97 pMC and >1.4 TU compared to 72-85 pMC and 0.68-1.03 TU, respectively), indicating potential anthropogenic inputs. Water stable isotopes, plot along a mixing line between regional groundwater (e.g. outside the known plume) and evaporated groundwater (e.g. recharge from former and current sludge lagoons). End-member mixing calculations indicate a significant proportion of effluent in groundwater downgradient of treatment infrastructure. Elevated nutrient concentrations in groundwater occur throughout the region (e.g., 0.6 to 160 mg/L nitrogen (total)). Nitrate isotopes show clear differences between nutrients derived from agriculture (values between 5 and 29‰, median = 12.0‰), and those impacted by the treatment plant (values between 2.9 and 41.2 ‰, median = 18.0‰), with effluent values between 20.2‰ and 39.1‰). Further work is being undertaken to quantify pharmaceuticals as an additional metric to better delineate wastewater impacts. Conclusions : The findings show how isotopic tracers can assist in overcoming the difficulties associated with delineating multiple similar contamination sources. This will enable wastewater treatment plant operators to more accurately assess and manage their impacts on groundwater. © The Authors