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IAEA Helps Researchers Worldwide Implement Sophisticated Isotope Techniques to Date the Age of Very Old Groundwaters

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Rim Trabelsi and her team from the Laboratory of Radio-Analysis and Environment of the National School of Engineers of Sfax in Tunisia sampling very old groundwater in the local aquifers. (Photo: Laboratory of Radio-Analysis and Environment team at the National School of Engineers of Sfax in Tunisia)

Nuclear techniques enable scientists to understand more accurately the age and flow of particularly old groundwaters. This information can prove important for the long-term management of water resources. Groundwater is the main source of freshwater in many places of the world, but it is a limited resource. Many developed and developing countries are actively seeking the best way to use clean groundwater as sustainably as possible, considering the risks associated with water shortage, pollution, or land subsidence. To this end, the IAEA, together with 13 countries, collected over 100 groundwater samples from aquifers worldwide and hosted a meeting in Vienna in June where 19 scientists presented their sampling results.

For assessing the age of very old groundwater, perhaps millions of years old, scientists find out the concentration of naturally-occurring radioisotopes, which decay very slowly and are not disturbed by chemical reactions within water and with surrounding rocks. In such cases, noble gases such as krypton and helium have been used increasingly as age tracers to estimate the time scales involved in groundwater flow. By analyzing the concentration of the certain isotopes, such as krypton-81 or helium-4 dissolved in groundwater, scientists can calculate precise time scales of when water was recharged in aquifers, how fast it flows, and how long it takes to replenish.

Water shortage is a constant problem in Tunisia and much of the available groundwater resources are shared among Algeria, Tunisia and Libya.

“Estimation of groundwater age will be very useful to calibrate existing groundwater flow models, which local authorities will be able to use for the sustainable management of water resources,” said Rim Trabelsi, Professor Assistant at the National School of Engineers of Sfax in Tunisia, who attended the meeting in Vienna. “We appreciate the IAEA’s support for sampling and analysis, and also look to develop our knowledge in the use of isotopes in water resources management through these training courses and meetings.”

A fellow participant, Sibele Ezaki, a researcher at Secretariat for the Environment of the State of Sao Paulo in Brazil, is conducting a study to estimate the date of groundwaters in the Tubarao aquifer in Sao Paulo State. The Tubarao aquifer faces on an urgent water shortage due to the rapid growth of population and industrial necessities. “Knowing views of other researchers enriched my knowledge in the field of groundwater assessment and allowed me to have a self-critical view of what can be done to improve our research,” said Ezaki.  “Our team is hoping to understand the hydrogeological behavior and recharge potential of this aquifer through a clear determination of its age.

Collecting sufficient amounts of groundwater samples and analyzing the concentrations of dissolved noble gases are technically difficult tasks for many researchers. This is because the amount of krypton and helium in groundwater is extremely small and its analysis requires state-of-the-art equipment, which is not easily accessible for many Member States. The IAEA Isotope Hydrology Laboratory in Vienna is one of a few high-throughput laboratories in the world that can analyze the concentration of helium-4 dissolved in very old groundwaters. The Laboratory also operates techniques and equipment that can sample and purify krypton-81 extracted from groundwaters.

“Understanding the time dimensions of deep groundwater brings us better assessment on groundwater flow models to tackle water needs and problems in various regions” said Takuya Matsumoto, Analyst at the IAEA Isotope Hydrology Laboratory. “Using noble gases for dating groundwater age is relatively new, so we need more samples and case studies to enhance the reliability of this method. This is one of this project’s objectives.”

The outcomes of this meeting are enhancing the understanding of non-renewable groundwater systems, and the Laboratory will facilitate the access to the analytical methods to many Member States. Additionally, the Laboratory will collect additional samples from locations selected at the meeting, sending IAEA experts and using special equipment developed at the Agency. “The IAEA Isotopic Hydrology Laboratory is hoping to help more researchers who need support for sampling and analysis of helium and krypton to ensure data integrity and consistency,” said Matsumoto.

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