Groundwaters in Cainozoic sand and gravel aquifers in the arid Ti-Tree Basin are becoming intensively used for irrigation. Carbon isotope chemistry indicates that most of the groundwaters in this basin were recharged in the Holocene. Estimated C-14 ages of the groundwaters range from modern to 8910 years BP. The modern ages correlate with flood-out recharge situations. Elsewhere in the basin, groundwater age correlates with the depth to aquifer suggesting that diffuse recharge by direct infiltration may have occurred episodically from 1730 to 8910 years BP. Stable isotope parameters indicate that recharge took place during exceptionally heavy rainfall events, and that the recharging groundwaters were subject to evaporation prior to infiltration. Only limited recharge takes place in the modern climatic regime, and this needs to be considered in groundwater resource management.

Carbon isotope chemistry indicates episodic palaeorecharge of groundwater in the arid Amadeus Basin, central Australia. In this hydrogeologically complex region, groundwater has been recharged by three important mechanisms: direct infiltration of rainwater through sand dune cover or fissures in calcrete; through river bed sands following floods; and through joints in bedrock outcrops. Modern and Holocene groundwaters (0–5000 years B.P.) are found in the unconfined calcrete and sand dune aquifers which have evolved hydrochemically to Cl-SO4-Na waters with Ca and Mg, as a result of evaporative concentration. Holocene groundwaters (3–10,000 years B.P.) have been dated in river bed recharge situations; these groundwaters are mainly of the HCO3-Cl-Na type, with Ca and Mg, and preserve the hydrochemical signature of the flood recharge waters. Most groundwater sampled in the folded and jointed rocks of the basin has a low modern 14C content and was recharged in the Holocene and late Pleistocene (12–32,000 years B.P.). These waters are intermediate in their ionic composition, covering a spectrum between the HCO3-Cl-Na and Cl-SO4-Na types; solution is the dominant process int heir hydrochemical evolution. Stable isotope signatures and derived parameters indicate that the intensity of rainfall is an important factor in the evolution of arid-zone groundwaters. Modern reharged is limited implying that projected large scale groundwater development in this region will use an effectively nonrenewable resource and should be managed accordingly.

Physico-chemical data and isotopic studies (utilising H14CO3, H218O, 3H2O) suggest that hypersaline meromixis in Ellis Fjord (Vestfold Hills, Antarctica) was initiated during the middle Holocene period, when hypersaline brine, excluded during the annual formation of sea-ice, gravitated in a density current to the bottom. The application of this contemporary information to the genesis of the meromictic lakes found today in the Vestfold Hills, suggest that their meromixis may have developed prior to isolation from the sea. Comparison of physico-chemical data from the meromictic basins of Ellis Fjord with that of the Vestfold Hills saline lake allows some determination of their evolutionary pathways initiated before, during and after isolation from the sea. Further evolution of each lake can be explained through the individual interaction between climate, the catchment size and basin morphology.

An Accelerator Mass Spectrometry system has been developed using the 14UD tandem accelerator at the Australian National University. It has been used for 36Cl measurements on groundwater samples from the Murray Basin in southeastern Australia. Measurements of 14C have also been made on the same groundwaters. The information can be combined with stable isotope ratios and other data to illustrate the occurrence of processes such as radioactive decay and local recharge in different aquifers.

The chlorine-36 measurement system at the Australian National University is described and some early results are presented.

Environmental radiocarbon was used to study aspects of groundwater origin, transport and mixing in the aquifer system underlying northern Victoria. The clearing of native vegetation and the advent of irrigation on the northern plains have upset the hydrological balance, caused water tables to rise and in some areas caused the waterlogging and salination of the land. Groundwater shallower than 30 m only yielded modern radiometric dates. Groundwater in the ‘Calivil/Renmark Aquifer’ in the Loddon and Goulburn Valleys has yielded ages up to 20 000 years and has a flow rate between 0.13 and 0.01 m day‐1. These values agree with the mean pore velocity calculated using Darcy's Law.

The use of the tracer dilution technique to gauge flow over broad shallow floodplains is examined. Because of the long mixing lengths, it sometimes takes several days for the passage of the laterally dispersed pulse. Tracer methods can be used if the flow rates vary linearly during the passage of the pulse. The measured flow rate is related to the time at which the first moment of the concentration profile (∫tc(z,t)dt) is zero. An experimental verification is presented.

The Australian Atomic Energy Commission has undertaken a number of studies using low level radioisotope techniques to assist in the assessment of waste disposal systems. The studies have varied, from the assessment of established systems where problems such as the beach deposition of ocean borne sewage effluent and the suitability of dumping sites for dredged spoil can be investigated, to the prediction of the impact of proposed systems where, for example, the effects of the discharge of waste water from mining operations into a flood plain system can be gauged.

The town of Alice Springs is situated within the arid zone of central Australia and derives its water supply from production bores in Mereenie Sandstone. Twenty-nine samples of this water and other surrounding water have been analysed for their chemical, radiocarbon, stable carbon, deuterium and 18O composition to investigate recharge to the aquifer system.

The standard ASTM method is the most commonly applied method for determining 222Rn in drinking water. The method is calibrated with a 226Ra standard solution that usually contains variable amounts of 210Pb, 210Bi and 210Po if the standard has not recently been purified. Until now it has not been experimentally confirmed that these progenies do not interfere when the method is calibrated. In this study, interference was examined using three different organic cocktails and α/β liquid scintillation spectrometry to separately assess the effect of three radionuclides. The interference from 210 Po was 4% for one of the cocktails if the 226Ra standard had been purified 5 years earlier. The interferences from 210Pb and 210Bi were negligible compared to that of 210Po.