Growing pressure on groundwater resources worldwide necessitates detailed characterization and quantification of groundwater fluxes and dynamics. The complexity of interactions between water bodies poses questions which can best be answered in the context of a consolidated integrated approach using tools and techniques from geology, geography, hydrogeology and hydrology. Since the turnover time of groundwater in an aquifer is directly related to volume and sustainable yield, this parameter is of high importance. In the context of large land use changes, population growth and climate change, a direct evaluation of the replenishment rate of groundwater on short time scales provides very important information for water resources management.
The most prominent current tracer for young water is the Tritium/3He (3H/3He) technique, combining time-dependent tritium input from atmospheric water with tritium decay into 3He within groundwater. The 3H/3He technique is applicable over a relatively wide time range, from a few years to several decades. However, application of this valuable tool for understanding hydrogeological systems also presents challenges in terms of sample collection and analysis, along with the availability of local analytical laboratories.
To facilitate the use of noble gas isotopes as part of water resource assessments, the IAEA Water Resources Programme established its own noble gas analytical facility at the Isotope Hydrology Laboratory and initiated this Coordinated Research Project (CRP). Experts from 11 countries participated in the CRP, and more than 300 3H/3He age data were produced during the five years of the project, resulting in a unique dataset that spans diverse environments. In some cases, such as in Croatia, Macedonia and the UK, the obtained 3H/3He ages are compared with other age tracers (e.g., CFCs, SF6 and tritium), thus demonstrating their advantages and limitations (Fig. 1). Attempts were made to incorporate the obtained 3H/3He ages into a conceptual groundwater model aiming at a better understanding of the targeted aquifer systems in the UK, the Czech Rep. and Macedonia. In addition, precipitation samples collected after the Fukushima Daiichi Nuclear Power Plant accident in 2011 from several Japanese sites were examined for their tritium and 129I contents as a part of this CRP. This study assessed the impact of environmental tritium release by the accident, which can potentially affect the application and interpretation of future 3H/3He age data in Japan.
The CRP not only advanced the understanding of the hydrology of the study sites by providing a new age information based on the noble gas technique, but also helped the Isotope Hydrology Laboratory to establish its noble gas analytical facility and its robust work flow to routinely produce high quality noble gas isotope data for age dating purposes. Currently, the facility is producing a full set of noble gas isotope data from about 300 samples per year which is open to water resource authorities and scientists from IAEA Member States. The results contributed to a wider use of the noble gas methodology on a routine basis for better water resources management, including via IAEA Technical Cooperation projects.
Researchers from Argentina, Croatia, the Czech Republic, France, Hungary, Japan, Morocco, North Macedonia, Pakistan, Turkey, the United Kingdom and the United States of America participated in this CRP.
For more information, please see the CRP description:
https://www.iaea.org/projects/crp/f33018