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The challenge

Characterising groundwater flow on time scales that date back a million years requires new technology for detecting noble gas isotopes

The complexity of natural groundwater systems and the limitations of many traditional environmental tracers calls for the use of a new suite of 'ideal' tracers: the noble gases. These are the most reliable tracers to investigate groundwater history, quantify recharge processes and determine the degree of aquifer interconnectivity. Two families of noble gas tracers exist: stable and radioactive.

Vials of gases taken from water samples, ready for analyses. Pictured at the Noble Gas Facility at the Waite campus in Adelaide. ©  James Knowler + Crew

Stable noble gases: The noble gases helium (He), neon (Ne), argon (Ar), krypton (Kr) and xenon (Xe) don’t show chemical alterations and allow reconstruction of infiltration conditions such as the soil temperature thousands of years ago. This makes their use superior to the traditional tracers. The isotope 4He has been the workhorse for many groundwater studies. Increased demand for such analysis, and the need for greater accuracy, required us to develop a new noble gas facility with greater output, better efficiency and improved accuracy. At the same time, the need to quantify the age of much older fluids required that additional isotope ratios of the noble gases be added (for example 21Ne,20Ne, 38Ar,40Ar,136Xe,132 Xe) to further our measurement capability.

Radioactive noble gases: The noble gases argon and krypton have three radioactive isotopes (85Kr, 39Ar and (81Kr) that are amongst the most difficult to measure because of their very low concentration. They can be used to determine the origin of water or polar ice tracing back decades (85Kr), centuries (39Ar) or up to one million years (81Kr). The challenge with traditional measurement technology for radiokrypton and radioargon is that large amounts of water (several tons) need to be sampled to achieve sufficient accuracy making this technique inefficient, time consuming and hence a limited analytical capability exists worldwide.

Our response

Combining the environmental tracer capabilities of CSIRO and several universities in cross disciplinary partnerships while championing the latest technologies

We developed a state-of-the-art noble gas facility for stable noble gases and supported the development of the Atom Trap Trace Analysis Facility (ATTA) for radioactive noble gases.

The Noble Gas Facility with its high-resolution mass spectrometer Helix-MC, located at the CSIRO Waite Campus, Adelaide. ©  Nick Pitsas

Noble Gas Facility

This facility at CSIRO's Waite campus in Adelaide was designed for high sample throughput and high accuracy. It measures the stable noble gases and all their stable isotopes, is completely computer controlled with all raw data and results stored and archived in a dedicated laboratory management and database system. This management and database system also has tools for interpreting and modelling the results. In 2019 the facility was further enhanced with a high-resolution multi-collector static noble gas mass spectrometer (Helix-MC plus) . This allows measurement of the rare noble gas isotopes 3He, 21Ne or the rare xenon isotopes such as 126Xe, 128Xe, 129Xe, and 130Xe. Recent improvements include a larger multiport system for higher sample throughput and the development of a mineral crushing system to measure noble gases in fluid inclusions of minerals.

ATTA Facility

This facility at The University of Adelaide uses the latest laser technologies to drive the successful application of radioactive noble gas tracers for natural groundwater systems. CSIRO scientists along with researchers and engineers at our partnering institutions (The University of Adelaide and Griffith University) combine laser-physics based atom excitation, trapping and detection to selectively separate and individually count the targeted atoms of 85Kr, 39Ar and 81Kr. These technologies, derived from recent years of high profile applied physics, quantum information and computing, can take direct measurements of the purified Ar and Kr fractions of environmental samples. Since the technique captures single atoms in a magnetic field and crossed laser beams, it is labelled Atom Trap Trace Analysis (ATTA). This unique facility – only the second of its kind to measure both radioargon and radiokrypton - is a leap forward in groundwater research.

[Music plays and an image appears of the CSIRO logo on a black screen]

[Image changes and new text appears: The Noble Gas Facility, Window to the Past]

[Image changes to show a view of an Australian landscape from a moving helicopter]

Narrator: Australia is ancient and flat.

[Image changes to show a view looking down on a riverbed]

Beneath its surface is slowly moving groundwater that can be up to 2,000,000 years old, some of the oldest water on the planet.

[Image changes to show water spurting from a tap in a dry landscape and then the image changes to show sprinklers irrigating a green crop]

Groundwater provides 30% of Australia’s water supply.

[Image changes to show a view looking down on a river and the camera slowly pans up the river]

But is that groundwater and rivers and springs fed by groundwater being used sustainably?

[Image changes to show two males walking down a corridor in conversation and then the image changes to show a male working in the Noble Gas Facility]

These questions and many more can now be tackled with unparalleled accuracy.

[Camera pans around the equipment in the Noble Gas Facility and then the image changes to show the Helix machine and then the camera continues to pan around the room and text appears: CSIRO Adelaide, Helix Facility]

Two new facilities have been added to an already unique Noble gas laboratory, making this combined research facility one of the most comprehensive Noble gas labs in the world.

[Image changes to show a view looking up into a cloudy sky and then the image changes to show water running over rocks]

When rain falls, some of it seeps into the ground and accumulates within porous rocks called aquifers.

[Image changes to show a view of a river and then the image changes to show a pump operating to pump the water]

Eventually this groundwater may reach the surface naturally or by extraction.

[Image changes to show a tap spurting water in a dry landscape and then the image changes to show a large sprinkler irrigating a lush crop]

Depending on the quality of the water and the amount it can be used for human consumption, stock water supplies, irrigation or in mining.

[Image changes to show a front and then rear view of a tractor ploughing a paddock and then the image changes to show a body of water]

As Australia is the driest inhabited continent in the world groundwater is essential to meeting its water needs in most parts of the continent.

[Image changes to show a cracked dry lakebed and the camera pans over the surface]

With climate change and prolonged droughts surface water is becoming increasingly scarce so the use of groundwater is rising.

[Images move through to show a crocodile sitting in some water, a white water bird standing in amongst plants in the water, and then a pink water lily]

Knowing whether a source of groundwater is sustainable is vital.

[Image changes to show the Noble Gas Facility equipment and the camera pans around the room and then the image changes to show text on the screen: Helium, Argon, Neon, Xenon, Radon, Krypton]

And the key to determining the age and movement of water that can be from tens of years to millions of years old is to analyse traces of certain gases in the water which are collectively known as Noble gases because they don’t easily react with anything.

[Yellow dots appear moving over the words and the words disappear leaving a blank screen]

This makes them ideal traces for groundwater studies.

[Image changes to show a view looking down into bubbling water]

Analysing Noble gases can tell us the history of Australian groundwater, its origins and how it has moved underground.

[Image changes to show two males setting up and operating some equipment outside and the camera zooms in on one of the male’s working on the equipment and then the camera zooms in]

The process starts in the field where sophisticated equipment can be used to extract large volumes of gas directly from a groundwater source.

[Images move through to show a male turning the tap on the equipment, a water sample being taken from a river by a person in a helicopter, and the person inside the helicopter holding the sample]

Alternatively water samples can simply be collected in the field in copper tubes that are tightly clamped off to ensure there is no contact with air.

[Image changes to show a male operating equipment in the Helix Facility and the camera zooms in on the equipment and then on the male at work and text appears: CSIRO Adelaide, Helix Facility]

The water samples are put in a gas preparation line where the gas is extracted using liquid nitrogen to freeze the water.

[Image changes to show a male turning the tap on the side of the machine and the camera zooms in on the male’s face and then on the tap he is turning on]

The Noble gas machine then separates individual gases at extremely cold temperatures.

[Images move through to show the male walking to a computer and looking at the screen, the Helix MC Plus machine, and a female and the male looking at the computer screen]

Once separated the new state of the art high resolution Helix mass spectrometer blasts each gas with electrons to measure the ratio of atomic variations, or isotopes of each gas at unprecedented resolution.

[Camera zooms in on the computer screen showing a diagram on the screen]

And it is these distinct ratios of Noble gases that define precise periods in the earth’s history.

[Image changes to show two males working on equipment in the Noble Gas Facility and then the image changes to show a hand operating a touch screen showing a wavy line type graph]

It’s now possible to investigate deep fluids that are more than several hundred million years old.

[Images move through of people walking along past a multi-windowed large building, two males walking towards the camera down a corridor, and equipment inside the Gas Facility and text appears: University of Adelaide, Atom Trap Trace Analysis Facility (ATTA)]

The Noble Gas Facility extends to the University of Adelaide Campus at North Terrace where teams from the University and CSIRO are finalising the Atom Trap Trace Analysis or ATTA Facility.

[Image changes to show a male working on the equipment and the camera zooms in on his face as he looks down]

ATTA uses advanced laser physics to measure Noble gases.

[Image changes to show the equipment again and the camera pans along the equipment to the male working on the equipment]

It complements the CSIRO equipment by targeting other isotopes of krypton and argon that exist only at ultra-low concentrations making them very difficult to measure.

[Image changes to show two males talking together inside the Facility]

However, through the ATTA Facility precise measurements become feasible and practical.

[Image changes to show a chart on a computer screen]

It is now possible to date groundwater samples from 1,000,000 years to just a few decades old.

[Image changes to show the two males working around the equipment in the Facility and the camera pans over the equipment in the room]

Because ATTA and Helix measure totally different Noble gas isotopes an unprecedented set of precise tools becomes available for Australian scientists.

[Image changes to show a map of Australia showing the Fitzroy, Darwin and Mitchell catchment areas on the map and then the image changes to show sprinklers irrigating a lush crop]

The Northern Australian Water Resource Assessment or NAWRA was a major government study to identify potential development opportunities such as irrigated agriculture that would need reliable and sustainable water supplies.

[Image changes to show Dr Chris Chilcott talking to the camera and text appears: Dr Chris Chilcott, CSIRO Research Leader for Northern Australia]

Dr Chris Chilcott: So, the new facilities are a fantastic resource for all groundwater researchers across Australia and particularly in the north where we don’t know much about the groundwater sources. It allows us to understand the sources of water, where they’re from, the age of the water, and what the recharge rates are and that then allows us to make decisions about sustainable extraction.

[Image changes to show a tap in a dry landscape spurting a stream of water]

And then that leads on to giving us opportunities for irrigated agriculture.

[Image changes to show three colleagues working in the snow with a snow vehicle in the background and text appears: Intrepid Science]

Narrator: And it’s not just limited to analysing water.

[Image changes to show a view of an Antarctic landscape and then the image changes to show a view looking down into an ice core]

The facility can be used to look further into the past of Antarctica’s climate by measuring age markers from gases trapped in Antarctic ice cores.

[Music plays and the camera zooms into the hole in the ice core]

[Image changes to show the equipment in the Noble Gas Facility and the camera pans around the room to show the equipment and then the image shows a male looking at the equipment in operation]

The recent investments in the joint CSIRO, University of Adelaide Noble Gas Facility, with new tools like the ATTA and Helix machines, will provide Australian researchers, government and businesses with a unique capability for collaboration on national water challenges.

[Image changes to show a male and female looking at a computer screen and then the image changes to show a view of a ute parked next to a water testing site in a paddock]

The knowledge the Noble Gas Facility provides will help protect our groundwater from overuse or contamination.

[Image changes to show a view looking down on a tractor towing a piece of equipment in a paddock]

It is a window to the past that will help secure Australia’s future.

[Image changes and the CSIRO, University of Adelaide, Science and Industry Endowment Fund and Australian Government Australian Research Council logos and text appears: CSIRO noble gas analysis capability is a joint partnership with the University of Adelaide. This research is supported by the Science and Industry Endowment Fund, The Atom-Trap Analysis Facility (ATTA) at The University of Adelaide was partially funded under the Australian Research Council’s Linkage Infrastructure, Equipment and Facilities scheme]

[Music plays and the CSIRO logo and text appears: CSIRO Australia’s innovation catalyst]

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The results

The new facilities are hailed a success in first case studies

The capability of the ATTA facility incorporates the latest technology for groundwater sampling, gas separation, and noble gas purification.

In addition, the facility for stable noble gases has been producing data since mid-2016 and these measurements drove scientific results in multi-tracer studies in nearly all states and territories. Since 2019 also the rare isotopes 3He and 21Ne were routinely measured and provided additional information about the origin of helium and neon in groundwaters, identifying deep primordial sources. Details of applications in NSW, NT, QLD, SA and WA can be found on the Environmental Tracers homepage.

The CSIRO tracer team developed field sampling equipment capable of extracting 40 litres of dissolved gases from approximately two tons of water in the field. Transporting such large amounts of groundwater to the lab would not be feasible, so field extraction was a necessary step in the technology. The subsequent purification of the gas (to produce purified microlitre Kr and decilitre Ar fractions) is based on a large-scale gas chromatographic system at the CSIRO Waite laboratories.

Researcher Dr Rohan Glover with the Atom Trap Trace Analysis (ATTA) facility at The University of Adelaide ©  Nick Pitsas

In collaboration with CSIRO and Griffith University, the ATTA facility (located at The University of Adelaide at the Institute for Photonics and Advanced Sensing) is in its testing phase. It will undergo further development to reduce the need for collection of large groundwater samples even more, i.e. down from 1-2 m3 at present to only a few tens of litres.

The application of 85Kr in groundwater system science in Australia requires a known input function (known concentrations entering groundwater via rainwater). We have developed this time series since July 2015 at CSIRO's Waite Laboratories. The measurement of this isotope 85Kr involved a collaboration with the German Federal Office for Radiation Protection (Bundesamt für Strahlenschutz).

A first pilot study using 85Kr targeted the freshwater lens in Rottnest Island (Perth). This involved purifying the samples at CSIRO while 85Kr was measured at the University of Bern, Switzerland. Rottnest Island, a national park and popular tourist destination, has a freshwater lens under it that sits atop seawater like a drop of grease on soup.

A second pilot study involved sampling the aquifers of the eastern recharge region of the Great Artesian Basin (Pilliga Sandstone, NSW). Following gas separation in the field, gas samples were processed at the CSIRO Waite laboratories and the Kr fractions were analysed at the University of Science and Technology in Hefei, China. The isotope 81Kr was used to characterise the regional groundwater system on the timescale of millennia. It revealed two flow paths whose groundwater velocities differed by an order of magnitude, each representing regions with a different recharge condition.

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