New stable and radioactive noble gas tracers at CSIRO

Full text: CSIRO is Australia's leading pioneer of new applications of environmental tracers in groundwater, surface water and aquitard pore water for nearly four decades. This involved adapting dynamically to the needs of our customers – state agencies and industry partners. Our group pioneered in the application of stable isotopes, later of 14C and 36Cl. Their commercial availability made our group shift to the less common, most useful tracers. The most recent step of this continuous adaption moved us into the role of the only laboratory on the southern hemisphere to supply measurements of stable noble gases (He, Ne, Ar, Kr, Xe) and radioactive noble gas isotopes (85Kr, 39Ar, 81Kr) in (ground)water samples. Noble gases are the most versatile tool among the environmental tracers. They allow assessing flow velocities on time scales from years (85Kr), centuries (39Ar), millennia (4He) up to one million years (81Kr) and beyond (4He, 40Ar, 21Ne, 134Xe, 136Xe). Knowing flow velocities is indispensable in managing groundwater as a resource for drinking water, agriculture, industry and mining. Noble gases also allow reconstructing infiltration conditions (temperature, salinity, altitude) and distinguishing infiltration processes, like recharge after flooding a dry riverbed versus constant infiltration from a permanently loosing stream. As such they are indispensable tools in any groundwater assessment, in the study of surface water – groundwater interaction, groundwater – sea water interaction, assessing aquitard permeability, aquifer systems and the calibration of numerical models for groundwater flow and transport. The talk will give details of the new analytical facility at CSIRO Waite campus, demonstrating why it is better adapted to Australian groundwater problems than the few existing overseas laboratories. It will demonstrate how the new tracers fit into multi-tracer studies with other more common tracers (18O/2H, 3H, CFCs, SF6, 14C, 36Cl): these need noble gas information and noble gases are more robust because chemically inert. Application details will be given in talks by other authors of the team within the context of single projects and case studies. (author)