Browsing by Author "Hofmann, H"
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- ItemGeochemical influences on methanogenic groundwater from a low rank coal seam gas reservoir: Walloon Subgroup, Surat Basin(Elsevier B. V., 2021-08-10) Baublys, KA; Hofmann, H; Esterle, JS; Cendón, DI; Vink, S; Golding, SDHydrochemical data responds at a much slower rate to changes in groundwater conditions than does the propagation of hydraulic pressure, and therefore may provide more insight to groundwater flow paths. In low rank coal measures, where gas is biogenic, it is important to understand the fluid-rock and microbial interactions that affect the spatial and temporal distribution of groundwater composition. Pressure data may not reflect true groundwater conditions pre-anthropogenic influence, nor does it provide information on the main drivers of groundwater composition, actual aquifer behaviour or even prove groundwater flow. This study uses a process-based approach to interpret a combination of tracer (36Cl, 14C, 87Sr/86Sr, 18O/16O) and hydrochemical data obtained from coal seam gas production wells to identify the main geochemical processes and thus controls on the groundwater composition in different coal seam producing areas of the Walloon Subgroup, Surat Basin, Australia. This is arguably one of the largest coal seam gas producing regions in the world. Tracer data measured in this study show that the Walloon Subgroup behaves as a stagnant aquitard, as indicated by the almost total loss of cosmogenic tracers over relatively short groundwater flow distances (~15 km), suggestive of very low ground water flow velocities. The range of 36Cl is 9.0 to 23.8 (x 10−15) while the 36Cl values across the Undulla anticline in the eastern edge of the basin, are essentially the same (12.2–14.7) within analytical error. It is argued that these isotopic values represent secular equilibrium for the Walloon Subgroup. Radiometric carbon (14C) levels across all three production areas (Roma, Undulla Nose, Kogan Nose) are also too low (range = 0.12–1.95 pMC) for viable field interpretation largely owing to the long residence time of the groundwater and the local activity of methanogens. Groundwater flow velocity was estimated to be <0.1 m/y, which is significantly less than the 0.7 m/y recently reported for the underlying Hutton Sandstone. As a result of the low groundwater flow velocities, trends in geochemistry are visible only in production regions proximal to the subcrop. At flow distances greater than 10–15 km from subcrop, several low-temperature interactions (cation exchange, silicate weathering, matrix diffusion and hyperfiltration) start to influence groundwater composition. Shallow subsurface chemical and microbial reactions may initially dominate the geochemical composition of the meteoric groundwater, but this is then overprinted by the actions of sulfate reducers and methanogens, resulting in groundwater with the typical geochemical characteristics similar to other coal bed methane groundwater in basins across the world (low SO4, Ca, Mg and high HCO3, Na, Cl). As distance and depth increase further, low temperature fluid-rock interactions then begin to influence the groundwater composition. This holistic, process-based approach applied to a combination of cosmogenic and stable isotopes, and standard hydrochemical data interpreted against basin lithology has enabled a more comprehensive picture on the behaviour of the groundwater of the Walloon Subgroup and is applicable to the study of other sedimentary basins. © Crown Copyright 2021 Published by Elsevier B.V
- ItemGroundwater mean residence times of a subtropical barrier sand island(European Geosciences Union, 2020-03-19) Hofmann, H; Newborn, D; Cartwright, I; Cendón, DI; Raiber, MFresh groundwater on barrier islands is affected by changing sea levels and precipitation variability due to climate change and is also vulnerable to anthropogenic processes, such as contamination and groundwater over-abstraction. Constraining groundwater mean residence times (MRTs) and flow paths is essential for understanding and managing these resources. This study uses tritium (3H) and carbon-14 (14C) to determine the MRTs of groundwater along a transect across subtropical North Stradbroke Island, south-east Queensland, Australia. Hydraulic properties, major ion geochemistry and stable isotopes are used to validate residence times and to identify the processes responsible for their variability. 3H activities range from less than 0.01 to 1 TU (tritium units), which are values lower than those of local average rainfall (1.6–2.0 TU). 14C concentrations range from 62.5 to 111 pMC (percent modern carbon). Estimated MRTs determined using lumped parameter models and 3H activities range from 37 to more than 50 years. Recharge occurs over the entire island, and groundwater MRTs generally increase vertically and laterally towards the coastal discharge areas, although no systematic pattern is observed. MRTs estimated from 14C concentrations display similar spatial relationships but have a much greater range (from modern to approximately 5000 years). Water diversion and retention by lower-permeability units in the unsaturated parts of the dune systems are the most likely course for relatively long MRTs to date. The results indicate that the internal structures within the dune systems increase MRTs in the groundwater system and potentially divert flow paths. The structures produce perched aquifer systems that are wide-spread and have a significant influence on regional recharge. The geochemical composition of groundwater remains relatively consistent throughout the island, with the only irregularities attributed to old groundwater stored within coastal peat. The outcomes of this study enhance the understanding of groundwater flow, recharge diversion and inhibition for large coastal sand masses in general, especially for older sand masses that have developed structures from pedogenesis and dune movement. With respect to south-east Queensland, it allows the existing regional groundwater flow model to be refined by incorporating independent MRTs to test models' validity. The location of this large fresh groundwater reservoir, in dry and populous south-east Queensland, means that its potential to be used as a water source is always high. Background information on aquifer distribution and groundwater MRTs is crucial to better validate impact assessment for water abstraction. © Author(s) 2020
- ItemA multi-tracer approach to quantifying groundwater inflows to an upland river; assessing the influence of variable groundwater chemistry(John Wiley & Sons, Inc., 2013-11-27) Atkinson, AP; Cartwright, I; Gilfedder, BS; Hofmann, H; Unland, NP; Cendón, DI; Chisari, RUnderstanding the behaviour and variability of environmental tracers is important for their use in estimating groundwater discharge to rivers. This study utilizes a multi-tracer approach to quantify groundwater discharge into a 27 km upland reach of the Gellibrand River in southwest Victoria, Australia. Ten sampling campaigns were conducted between March 2011 and June 2012, and the distribution of 222Rn activities, Cl and 3H concentrations imply the river receives substantial groundwater inflows. Mass balances based on 222Rn, Cl and 3H yield estimates of groundwater inflows that agree to within ± 12%, with cumulative inflows in individual campaigns ranging from 24 346 to 88 467 m3/day along the studied river section. Groundwater discharge accounts for between 10 and 50% of river flow dependent on the time of year, with a high proportion (>40 %) of groundwater sustaining summer flows. Groundwater inflow is largely governed by regional groundwater flowpaths; between 50 and 90% of total groundwater inflows occur along a narrow 5–10 km section where the river intersects the Eastern View Formation, a major regional aquifer. Groundwater 222Rn activities over the 16 month period were spatially heterogeneous across the catchment, ranging between 2000 Bq/m3 and 16 175 Bq/m3. Although groundwater 222Rn activities display temporal variation, spatial variation in groundwater 222Rn is a key control on 222Rn mass balances in river catchments where groundwater and river 222Rn activities are within an order of magnitude of each other. Calculated groundwater discharges vary from 8.4 to 15 m3/m/day when groundwater 222Rn activities are varied by ± 1 σ. © 2013 John Wiley & Sons, Ltd.
- ItemSources and transit times of water in headwater temperate rainforest streams(Copernicus Publications, 2019-04-07) Cartwright, I; Atkinson, AP; Gilfedder, BS; Hofmann, H; Cendón, DI; Morgenstern, UHeadwater catchments are important sources of water for many river systems. Unlike lower reaches of rivers that are frequently connected to alluvial aquifers, headwater catchments are commonly developed on indurated rocks that lack extensive groundwater systems. The observation, however, that many headwater streams are perennial implies that streamflow is sustained by water contained in fractures, soils, and/or the regolith. Understanding the sources and transit times of water that generates streamflow in headwater streams is important for understanding catchment functioning and predicting the response of catchments to changing climate or land use. This study determines water sources and transit times in first-order streams from a temperate rainforest in the Otway Ranges, southeast Australia. Comparison of the major ion geochemistry of soil water, water flowing through soil pipes (macropores), and groundwater from the riparian zone adjacent to the stream indicates that water from soil pipes is the major contributor to streamflow. By contrast, riparian zone groundwater and water from elsewhere within the soils contributes little to streamflow. The streams are gaining and the lack of riparian zone groundwater inputs may be due to the presence of low hydraulic-conductivity organic-rich streambed sediments or compartmentalisation of shallow groundwater by clays in the weathered rocks. Similarly, pockets of isolated water within the soils that are not connected to the soil pipes also exist. The stream water has tritium (3H) activities of 1.80 to 2.06 TU, with slightly higher activities recorded during the higher winter flows. The water from the soil pipes has 3H activities of 1.80 to 2.25 TU, the riparian zone groundwater has 3H activities of 1.35 to 2.39 TU, and one sample of soil water has a 3H activity of 2.22 TU. The 3H activities of all these catchment waters are significantly lower than those of modern rainfall (2.6 to 3.0 TU), and mean transit times calculated using a range of lumped parameter models are between 3 and 57 years. These mean transit times are consistent with the waters being resident in the catchment for sufficient time for weathering reactions and evapotranspiration to occur. While the discharge from the soil pipes increases following periods of high rainfall, this water is stored for several years within the catchment before discharge (probably within the weathered regolith). Thus, the increase in discharge is not the simple transmission of recent rainfall through the macropores but mobilisation of younger stores of water as the catchment wets up. The long mean transit times of the stream water imply that it is derived from a relatively large store (>108 m3) and is buffered against year-on-year variations in rainfall. However, longer-term variations in rainfall or land use will likely impact streamflow. © Author(s) 2018. CC Attribution 4.0 license.
- ItemUnderstanding groundwater dynamics on barrier islands using geochronological data: an example from North Stradbroke Island, South-east Queensland(National Centre for Groundwater Research And Training, 2015-11-03) Hofmann, H; Newborn, D; Cartwright, I; Cendón, DI; Raiber, MFreshwater lenses underneath barrier islands are dynamic systems affected by changing sea levels and groundwater use. They are vulnerable to contamination and over-abstraction. Residence times of fresh groundwater in barrier islands are poorly understood and have mostly been assessed by modelling approaches and estimates without fundamental validation with chronological estimations. Assessing residence time and recharge rates will improve significantly our understanding of hydrological processes of coastal environments that will in turn allow us to make informed decisions on groundwater use and environmental protection. This project focused on groundwater recharge rates and residence times of the fresh water aquifer system of North Stradbroke Island, south-east Queensland, Australia. Groundwater bores, wetlands and submarine groundwater discharge points in the tidal areas (wonky holes) were sampled along a transect across the island and were analysed for major ion chemistry and stable isotopes (δ2H, δ18O, δ13C) in combination with 3H, 14C analysis and 222Rn. Calculated 3H using a 90% exponential-piston flow model and 14C ages range from 12 to >100 years and modern to 3770 years, respectively, indicating a highly heterogeneous aquifer system with mixing from low and high conductive areas. The major ion chemistry in combination with stable and radiogenic isotopes suggests that a significant groundwater component derives from the fractured rock basement and older sedimentary formations underlying the sand dunes of the island. The results help refining the conceptual and numerical groundwater flow model for North Stradbroke Island in this particular case but also demonstrate the possible complexity of barrier island hydrogeology.
- ItemUnderstanding the sources and transit times of water sustaining streamflow in upland catchments(National Centre for Groundwater Research And Training, & Australian Chapter International Association Of Hydrogeologists, 2019-11-24) Cartwright, I; Atkinson, AP; Gilfedder, BS; Hofmann, H; Cendón, DI; Morgenstern, UHeadwater catchments are important sources of water in many rivers. While headwater catchments are commonly developed on indurated rocks without extensive groundwater systems, the observation that many headwater streams are perennial implies that they are sustained by water in fractures, soils, or the regolith. Understanding the sources and transit times of water in headwater streams is important for understanding catchment functioning and predicting the impacts of changing climate or land use. This study uses major ion geochemistry and tritium (3H) to determine water sources and transit times in first-order streams in the Otway Ranges, southeast Australia. Comparison of the geochemistry of soil water, water from soil pipes (macropores), and riparian groundwater indicates that macropore flow is the major contributor to streamflow. The streams are gaining and the lack of riparian zone groundwater inputs may be due to the presence of low hydraulic-conductivity organic-rich streambed sediments or compartmentalisation of shallow groundwater by clays in the weathered rocks. Similarly, much of the soil water exists in isolated pockets of isolated water that are not connected to the soil pipes. The stream water has tritium (3H) activities of 1.80 to 2.06 TU. These are significantly lower than the 3H activities of modern rainfall (2.6 to 3.0 TU), even during the higher winter flows. The water from the soil pipes has 3H activities of 1.80 to 2.25 TU, the riparian zone groundwater has 3H activities of 1.35 to 2.39 TU, and one sample of soil water has a 3H activity of 2.22 TU. Mean transit times calculated using a range of lumped parameter models are between 3 and 57 years. Relatively long mean transit times are consistent with the major ion geochemistry that implies that waters are resident for sufficient time for weathering reactions and evapotranspiration to have occurred. While the discharge from the soil pipes increases following periods of high rainfall, the long mean transit times implies that this water is stored for several years within the regolith before discharge, with storage volumes estimated as >108 m3. Thus the increase in streamflow is not the simple transmission of recent rainfall through the macropores but mobilisation of existing catchment stores. The streams will be buffered against year-on-year variations in rainfall but are vulnerable to longer-term variations in rainfall or land use. Management of these catchments needs to consider the impacts on the macropores and the delayed responses caused by the large storage volumes. © The Authors
- ItemUsing 14C and 3H to understand groundwater flow and recharge in an aquifer window(Copernicus Publications, 2014-12-09) Atkinson, AP; Cartwright, I; Gilfedder, BS; Cendón, DI; Unland, NP; Hofmann, HKnowledge of groundwater residence times and recharge locations is vital to the sustainable management of groundwater resources. Here we investigate groundwater residence times and patterns of recharge in the Gellibrand Valley, southeast Australia, where outcropping aquifer sediments of the Eastern View Formation form an "aquifer window" that may receive diffuse recharge from rainfall and recharge from the Gellibrand River. To determine recharge patterns and groundwater flow paths, environmental isotopes (3H, 14C, δ13C, δ18O, δ2H) are used in conjunction with groundwater geochemistry and continuous monitoring of groundwater elevation and electrical conductivity. The water table fluctuates by 0.9 to 3.7 m annually, implying recharge rates of 90 and 372 mm yr−1. However, residence times of shallow (11 to 29 m) groundwater determined by 14C are between 100 and 10 000 years, 3H activities are negligible in most of the groundwater, and groundwater electrical conductivity remains constant over the period of study. Deeper groundwater with older 14C ages has lower δ18O values than younger, shallower groundwater, which is consistent with it being derived from greater altitudes. The combined geochemistry data indicate that local recharge from precipitation within the valley occurs through the aquifer window, however much of the groundwater in the Gellibrand Valley predominantly originates from the regional recharge zone, the Barongarook High. The Gellibrand Valley is a regional discharge zone with upward head gradients that limits local recharge to the upper 10 m of the aquifer. Additionally, the groundwater head gradients adjacent to the Gellibrand River are generally upwards, implying that it does not recharge the surrounding groundwater and has limited bank storage. 14C ages and Cl concentrations are well correlated and Cl concentrations may be used to provide a first-order estimate of groundwater residence times. Progressively lower chloride concentrations from 10 000 years BP to the present day are interpreted to indicate an increase in recharge rates on the Barongarook High. © Author(s) 2014.
- ItemUsing geochemistry to understand water sources and transit times in headwater streams of a temperate rainforest(Elsevier B. V., 2018-12) Cartwright, I; Atkinson, AP; Gilfedder, BS; Hofmann, H; Cendón, DI; Morgenstern, UUnderstanding the sources and transit times of water that generates streamflow in headwater streams is important for understanding catchment functioning. This study determines the water sources and transit times in first-order streams from a temperate rainforest in the Otway Ranges, southeast Australia. Comparison of the major ion geochemistry of soil water, water flowing through soil pipes (macropores), and groundwater from the riparian zone adjacent to the stream suggests that water from soil pipes is the major contributor to streamflow. The tritium (3H) activities of the stream water are between 1.80 and 2.06 TU, the water from the soil pipes has 3H activities between 1.80 and 2.25 TU, the riparian zone groundwater has 3H activities of 1.35–2.39 TU, and one sample of soil water has a 3H activity of 2.22 TU. These 3H activities are significantly lower than those of local modern rainfall (2.6–3.0 TU), and mean transit times calculated using a range of lumped parameter models are between 3 and 57 years. These estimates are consistent with the major ion and stable isotope data, which imply that mean transit times were sufficiently long to allow weathering of minerals and/or organic matter and evapotranspiration to occur. The long mean transit times imply that water flows in this upper catchment are buffered against year-on-year variations in rainfall, but may change due to longer-term variations in rainfall or landuse. © 2018 Elsevier Ltd.