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Characterising changes in isotope hydrochemistry through time in a high use, arid-zone aquifer
Stephen Hostetler 1 , Emily Slatter 1 , John Wischusen 2 1. Geoscience Australia, Symonston, ACT, Australia
2. Department of Environment and Natural Resources Northern Territory, Alice Springs, NT, Australia
Alice Springs is an important centre for regional industry, tourism and transport in the Northern Territory. The town has approximately 29,000 inhabitants and
400,000+ visitors are wholly reliant on groundwater from aquifers in the Amadeus Basin. Current groundwater use in the Roe Creek Management Zone borefield is
~8,500 ML/yr, far in excess of the ~750 ML/yr of groundwater recharge to the area.
As a result, groundwater levels in the Roe Creek borefield have fallen by ~1 m/yr since 1964.
As part of the Exploring for the Future program, Geoscience Australia flew ~2375 line km of AEM, drilled 3 boreholes, took 34 SNMR readings and collected 21 groundwater samples for hydrogeochemical analysis in the Alice Springs project area. Hydrochemistry samples were analysed for major and minor chemistry, stable isotopes, carbon-14, chlorine-36, tritium, CFCs and SF6. In addition, DENR NT have drilled a number of deep (500m) groundwater bores to analyse hydrogeochemistry and to monitor groundwater levels.
Over the last 40 years, there have been at least 4 generations of groundwater
sampling for chemistry, stable isotopes and radioisotopes in the Amadeus Basin. The earliest samples were collected by Calf in 1978, followed by Jacobson in 1989, BRS in 1999-2000 and Geoscience Australia in 2017-18.
During this period there have been at least 12 large rainfall events (> 150mm), although only the anomalously wet year of 1974 showed significant groundwater recharge in the Amadeus Basin, the water table has fallen by over 40 metres and many additional bores have been drilled or deepened. In addition, many older bores were indifferently constructed while modern bores are targeted to specific aquifers and intervals. This paper looks at how these changes are reflected in groundwater hydrochemistry and isotopic values and what these changes may mean to the management of groundwater in Alice Springs.
Understanding the sources and transit times of water sustaining streamflow in upland catchments
Ian Cartwright 1 , Alexander Atkinson 12 , Benjamin Gilfedder 3 , Harald Hofmann 4 , Dioni Cendon 5 , Uwe Morgenstern 6
1. Monash University, Clayton, VIC, Australia
2. Marchment Hill Consulting, Melbourne, VIC, Australia 3. University of Bayreuth, Bayreuth, Germany
4. University of Queensland, St Lucia, QLD, Australia 5. ANSTO, Lucas Heights, NSW, Australia
6. GNS Science, Lower Hutt, New Zealand
Headwater 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.
171 | P a g e 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.
Use of environmental tracers in environmental impact assessments for coal seam gas and large coal mining developments
Kelly Strike 1 , Carl Zimmermann 1
1. Department of the Environment and Energy, Parkes, ACT, Australia
In updating its Information Guidelines (2018) the Independent Expert Scientific Committee on Coal Seam Gas and Large Coal Mining Development (IESC) identified the lack of use of environmental tracers in developing conceptual and numerical models and how they can be used in a risk context to reduce uncertainty.
Confidently identifying and evaluating causal pathways to impacts on water-assets is key to an efficient environmental assessment process. Environmental water tracers can often complement other techniques and offer an important means of gaining multiple lines of evidence to support conceptual models. Importantly, in some
situations tracers may be the only feasible way of gaining information about systems at appropriate spatial and temporal scales. This presentation will provide an overview of the IESC’s environmental tracers factsheet, by explaining how tracers can be used in environmental impact assessments by:
1. outlining how tracers can fit into a risk-based framework; and 2. discussing five case studies where tracers have investigated:
172 | P a g e 1. surface and groundwater connectivity: estimation of groundwater
discharge into a section of the Gellibrand River, VIC;
2. recharge sources: the relationship between surface water in a marsh (asset), alluvial groundwater and deep groundwater in the Hamersley Basin, WA;
3. connectivity between different aquifers: groundwater movement between the coal seam and the alluvial aquifer in the Condamine River Catchment, Qld;
4. using tracers to constrain a water balance: evaporation from temperate highland peat swamps on sandstone in the Sydney Basin, NSW; and 5. improving groundwater modelling with tracer evidence: aquifers
intersected by dewatering bores at a mine-site in the Pilbara, WA.
References to further reading materials are provided for more detailed technical explanations.
Using environmental tracers to quantify recharge mechanisms and variation in the semi-arid Pilbara region
James McCallum 1 , Shawan Dogramaci 2 , Grzegorz Skrzypek 1 , Pauline Grierson 1 1. University of Western Australia, Perth, WA, Australia
2. Rio Tinto Iron Ore, Perth, WA, Australia
Recharge processes in arid and semi-arid environments are characterised by their high variability both temporally and spatially, making it difficult to determine appropriate components of water balances. However, quantifying recharge and understanding how recharge volume responds to changes in climate and hydrological regimes underpins accurate prediction of long-term water supply and water level recovery. We used environmental tracer techniques (including stable isotopes, radioisotopes, and anthropogenic compounds) to estimate ephemeral stream recharge processes in the Pilbara region of northwest Australia. We interpreted soil water profiles (> 6 m depth) of stable isotopes with a model of groundwater flow to assess recharge mechanisms and evapotranspiration in the riparian corridor of an ephemeral stream. We also used CFC-12 and 14C data coupled with a simple flow and groundwater-age model to investigate the change in groundwater recharge over time, with an emphasis on how the modified stream flow regime due to mining water discharge over the previous 10 years had altered groundwater recharge. The model applied an approach of correcting groundwater ages proportional to the flow rate in the system. We were able to identify that in upstream areas with (now) perennial surface flows, groundwater recharge was up to 200% greater than pre-mining conditions. At sites downstream where event-driven stream flow remains dominant, groundwater recharge was consistent with pre-mining conditions. Our results
indicate that the spatial variation of groundwater ages is indicative of temporal variation in groundwater recharge. The scales of variability identified in our study, corresponded to the time scales of variability in recharge concentrations of the measured tracers. However, applying a similar methodology with tracers of “old”
groundwater could give insight into variability of longer-term recharge.
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A golden age for environmental tracers in Australia
Sébastien Lamontagne 1
1. CSIRO, Adelaide, SA, Australia
Environmental tracers have been an integral component of hydrogeological studies in Australia for decades. However, the stage is now set for an unprecedented level of activity driven by the increased need for water resource assessments, new fields of investigation, and the recent availability of new tracer techniques. In water resource assessments, there is a need for more detailed groundwater system characterisation due to increased scrutiny of existing water allocation plans, resource development proposals, the proposed expansion of irrigation in Northern Australia, and a
dwindling resource under climate change. The planned trillion-dollar expansion of the unconventional gas industry in the coming decades will bring an increased focus on the connectivity between deep and shallower geological units and the slower
movement of fluids at depth – areas where tracers have many applications. Other national challenges where tracers could see broader use include groundwater contamination, mine site remediation, underground disposal of CO2 and nuclear waste, as well as rising sea levels and its effects on coastal cities and aquifers. The development of a new suite of analytical facilities in Australia to measure stable and radioactive noble gases opens many possibilities for new applications. These tracers have simple input functions, have no chemical reactions and are ideally suited to the evaluation of hydrological connectivity, recharge environments, or addressing the parts of the groundwater-age distribution invisible to other tracers. Despite a recognition of their usefulness, the cost, lack of expertise, and delays in obtaining results are current hurdles for a more effective uptake of tracer techniques by industry. Advanced training tailored to students, policy makers, and industry, coupled with a more robust infrastructure for the timely delivery of tracer analyses are the key ingredients required to enable a golden age for environmental tracers in Australia to blossom.
Partitioned mantle degassing through the Australian plate delineated by noble gas data
Karl E. Karlstrom 1 , Laura J. Crossey 1 , Tom Darrah 2 , Andy Love 3 1. University of New Mexico, Albuquerque, New Mexico, USA
2. Geology, Ohio State University, Columbus, OHIO, USA
3. Hydrogeology, Flinders University, Bedford Park, SA, Australia
Objectives: A compilation of new and published 3He/4He data in Australia reveals a surprisingly pervasive yet partitioned ongoing process of transfer of mantle-derived volatiles to the near surface groundwater system and into oil and gas reservoirs.
Design and Methodology: Comparison of helium isotope data with mantle
tomographic images show that high 3He/4He values in groundwater correlate with domains of low velocity mantle and with sharp mantle velocity contrasts.
Original data and results: Deep lithospheric boundaries (150-200 km) between high velocity mantle in western Australia and lower velocity mantle in eastern Australia, provide the first order control of mantle degassing and are interpreted to represent Precambrian structures that are currently being neotectonically reactivated (e.g.
Tasman line and Torrens hinge zone). Mid-lithospheric (75- 100 km) low velocity domains underlie zones of mantle degassing in central and western Australia. Rather
174 | P a g e than uniform upward flux of mantle volatiles into the lithosphere, our data delineate variably fertile mantle source regions and lithospheric conduit zones. Understanding the conduit systems for the deeply derived fluids require holistic geologic models, but we envision asthenospheric (MORB) sources in eastern Australia related to transfer of basaltic magma and accompanying volatiles from asthenosphere to lithosphere over the last several Ma. Helium leakage in non-volcanic areas is likely sourced from metasomatized lithospheric mantle. Helium and CO2 volatile transport through the crust takes place by (and facilitates) microseismicity, and water-rock interactions of deep geothermal fluids with hydrocarbons and deep basin brines introduce Cl, metals, and radiogenic Sr into aquifers. This continental scale fluid convection system is driven by small scale sublithospheric convection induced by plate
reorganization events related to initiation of transpression in New Zealand ~ 5 Ma and accompanied reactivation of lithospheric zones of weakness.
Hydrogeology: Implications involve a new paradigm for the Great Artesian Basin (GAB) which underlies 22% of the Australian continent and is one of the largest groundwater basins in the world. This new paradigm involves endogenic fluid inputs into the J-K aquifer system that leak up faults from below the aquifer, partition the GAB into hydrogeologic subbasins, and cause variable degradation of water quality.
Use of stable and radiogenic isotopes in characterising wastewater derived impacts in Urban and Peri-Urban areas
William G. McCance 1 2 , Oliver A.H. Jones 34 , Matt Edwards 2 , Aravind Surapaneni 5 , Sreenivasulu Chadalavada 6 , Dioni Cendón 7 , Matthew Currell 14
1. School of Engineering, RMIT University, Melbourne, VIC, Australia 2. BlueSphere Environmental, Southbank, VIC, Australia
3. Australian Centre for Research on Separation Sciences, RMIT, Melbourne, VIC, Australia 4. Water Effective Technologies & Tools Research Centre, RMIT University, Melbourne, VIC,
Australia
5. South East Water, Frankston, VIC, Australia
6. Cooperative Research Centre for Contamination Assessment and Remediation of the Environment, University of Newcastle, Callaghan, NSW, Australia
7. Nuclear Science and Technology, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia
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.
175 | P a g e 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.
1. Adebowale, T., et al. (2019). "Delineation of contaminant sources and denitrification using isotopes of nitrate near a wastewater treatment plant in peri-urban settings." Science of the Total Environment 651: 2701-2711.
2. McCance, W., et al. (2018). "Contaminants of Emerging Concern as novel groundwater tracers for delineating wastewater impacts in urban and peri-urban areas." Water Research 146: 118-133.
3. Cartwright, I., et al. (2017). "A review of radioactive isotopes and other residence time tracers in understanding groundwater recharge: Possibilities, challenges, and limitations."
Journal of Hydrology 555: 797-811.
4. Van Stempvoort, D., et al. (2013). "An artificial sweetener and pharmaceutical compounds as co-tracers of urban wastewater in groundwater." Science of the Total Environment 461- 462: 348-359.
5. Richards, S., et al. (2017). "Potential tracers for tracking septic tank effluent discharges in watercourses." Environmental Pollution 228: 245-255.
6. Kendall, C. and J. McDonnell (1998). Isotope Tracers in Catchment Hydrogeology.
Amsterdam, Elsevier Science.
7. Robertson, W., et al. (2013). "Persistence of artificial sweeteners in a 15-year-old septic system plume." Journal of Hydrology 477: 43.
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