Browsing by Author "Howcroft, W"

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    Differences in groundwater and chloride residence times in saline groundwater: the Barwon River Catchment of Southeast Australia
    (Elsevier B. V., 2017-02-20) Howcroft, W; Cartwright, I; Fifield, LK; Cendón, DI
    The residence times of groundwater and chloride and the processes contributing to the development of saline (total dissolved solids (TDS) up to 45,379 mg/L) groundwater within the Barwon River Catchment of southeast Australia were investigated using major ion, stable isotope (δ18O, δ2H, and δ13C) and radioactive isotope (3H, 14C, 36Cl) geochemistry. The elevated groundwater salinity in the region is primarily due to evapotranspiration and recycling of solutes in saline lakes with minor contributions from weathering of halite, silicate and calcite minerals. Groundwater residence times estimated from 14C vary from modern to ~ 20 ka; for groundwater with lower 14C activities, the estimated residence times vary significantly depending on the assumed flow model and the 14C activity of recharge. Chloride residence times downgradient of Lake Murdeduke (a saline through-flow lake in the centre of the catchment) are greater than the corresponding groundwater residence times due to the recycling of Cl within the lake. Precise estimates of chloride residence time could not be determined using 36Cl due to R36Cl in precipitation being lower than that of groundwater. This is most likely due to R36Cl values in rainfall having been higher in the past than they are at present due to climate variability. δ18O, δ2H, and δ13C values also suggest that the region has experienced increasingly more evaporative conditions with time. The results of this study demonstrate that, while Cl is a useful tracer of hydrological processes, it must be applied carefully in arid and semi-arid regions of the world. In particular, recharge rates calculated using chloride mass balance may be underestimated where recycling of Cl has occurred. Crown Copyright © 2017 Published by Elsevier B.V.
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    Residence times of bank storage and return flows and the influence on river water chemistry in the upper Barwon River, Australia
    (Elsevier B. V., 2019-02) Howcroft, W; Cartwright, I; Cendón, DI
    Documenting the sources and residence times of water that contributes to streamflow is important for understanding processes in river catchments. The residence times of bank storage and return flow and its influence on river water chemistry in the upper Barwon River of southeast Australia were investigated using stable (18O, 2H, and 13C) and radioactive (3H and 36Cl) isotopes, major ion geochemistry, river discharge data, and electrical conductivity (EC)-discharge hysteresis. Elevated 3H activities following high winter flows indicate that bank storage and return flow contributes to river discharge for at least several months. However, EC-discharge hysteresis patterns suggest that individual storm events make additional contributions to bank storage and return flow throughout the year over periods of a few weeks. 3H activities in the upper Barwon River are >1.75 TU throughout the year, suggesting that the contribution of older regional groundwater, which has 3H activities <0.04 TU, is relatively minor in comparison to bank return flows. However, downstream trends in total dissolved solids (TDS) concentrations, δ13C values and R36Cl values demonstrate that regional groundwater inflows deliver solutes to the river. Estimates of regional groundwater inflows are mainly in the range 8–33% of total stream flow. The R36Cl values of river water in the upper Barwon catchment are between 37 and 46, which are significantly higher than those of modern rainfall (∼20). The high R36Cl values may reflect retardation of bomb-pulse 36Cl due to plant uptake and recycling in the soil zone, which suggests Cl residence times of up to ∼60 years. The results of this study demonstrate that river water is comprised of both young and old water and that managing rivers and near-river environments should include careful consideration of both inputs. © 2018 Elsevier Ltd.
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    Selecting environmental water tracers to understand groundwater around mines: opportunities and limitations
    (Springer Nature, 2022-02-07) Kurukulasuriya, D; Howcroft, W; Moon, EM; Meredith, KT; Timms, W
    Underground mining operations have the potential to alter groundwater systems and facilitate hydraulic connections between surface water and groundwater. The nature and degree of these interactions need to be evaluated to identify mining risks to surrounding water resources and to predict potential operational effects and environmental impacts, such as hydraulic stress on local surface waters. Environmental water tracers (EWTs) are commonly used to study such interactions in mine water and hydrogeological studies. However, the opportunities presented by EWTs could be more widely utilised to benefit the mining industry and the environment. Some of the challenges faced include the lack of practical frameworks, the need for more examples of EWTs applications in mining, and the possibility of complex interpretation of tracer results. This paper reviews previous studies that have applied EWTs in groundwater systems within or near mine sites, mostly from Australia, China, and India. The EWTs used in these studies include water quality parameters, major ions, stable isotopes, radioisotopes, and dissolved gases. The opportunities of applying multiple EWTs to identify water sources, mixing, and determine recharge rates and groundwater residence times are discussed. Limitations of different EWTs in terms of their capabilities, reliability, cost of analysis, effort, and processing times are reviewed. Steps for selecting suitable EWTs for specific mine hydrogeology assessments should be commensurate with the risks. Finally, this paper provides an overview of suitable EWTs that will be a useful contribution to appropriate water resource management decisions around mines. © 2022 The Author(s)
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    Water tracer technologies to detect sources of seepage and protect environmental assets
    (University of Wollongong/University of Southern Queensland, 2021-02-02) Timms, W; Kurukulasuriya, D; Howcroft, W; Moon, EM; Meredith, KT
    Water tracer technologies can help optimise water management in coal mining operations and improve outcomes from environmental studies and controls to protect sensitive assets. ACARP project C28024 (Stage 1) is demonstrating how tracer analysis of groundwater and surface water can provide information on whether systems are hydrologically disconnected, partly connected or well connected. This stage of the project is focusing on conventional tracers that are often used by other mining industries around the world (e.g. iron ore, potash) and in groundwater resource studies. Stage 2 of this project proposes to test new artificial tracers combined with suitable conventional tracers that are particularly useful for identifying seepage sources for control actions. This paper will demonstrate and discuss the benefits and limitations of major groups of conventional tracers that are commonly measured naturally in water. These include: field parameters (e.g. electrical conductivity, temperature), major and trace ions (e.g. metals), stable isotopes of oxygen and hydrogen, industrial compounds (CFCs and SF6) and dissolved carbon isotopes (i.e. inorganic and organic forms). In addition, this paper will discuss radioisotope tracers (e.g. tritium, carbon-14 and radon-222), as robust and proven tools to help differentiate shallow and deep groundwater where there is a contrast in water residence time (groundwater ‘age’). These tracers can provide useful information on seepage, despite higher analysis costs and turn-around times for laboratory results. Key findings from demonstration mine sites show the importance of combining physical water measurements (e.g. water levels and pumping rates) with a suitable combination of water tracers, depending on the site specific issues or study questions. For example, artificial tracers that are added to water sources are most suitable for identifying seepage and rapid flow pathways that can be a risk to underground operations. However, common artificial tracers such as added salts and dye tracers can also raise community concerns, such as producing fluorescent green creeks. Novel artificial tracers are able to overcome these risks. For example, synthetic DNA with uniquely designed fingerprints can be released at different times and locations to identify the sources of water to excavations can then be controlled. Commensurate with the risks of the project, a combination of suitable tracer technologies of different types can increase the confidence in identifying water sources and flow rates underground. However, the costs, limitations and practical challenges of each proposed tracer should be considered in planning tracer studies. The outcomes of these ACARP projects will assist coal mining operators in deciding on the suitable combinations of tracers for different types of operational and environmental risks associated with underground mining, and show how tracer technologies can be used to check possible flow paths in conceptual and numerical models.