Petra Baják (PhD student, ELTE) visited the laboratory of one of the GTK‘s units named Circular Economic Solutions (CES) between 12 September 2021 and 24 September 2021. The purpose of her exchange was to learn how stable isotope measurements work and how the results can be evaluated and be involved in the mapping of groundwater flow systems. Prior to her visit, she collected 35 water samples following the sampling instructions given by Mia Tiljander (Senior Scientist, CES) and sent them to the GTK. 

After arriving at the GTK, she first got acquainted with the GTK’s facilities and gained insight into the operation and ongoing projects of two units of the GTK (Water Solutions and Circular Economic Solutions). She later visited the rainwater harvesting station of the GTK, which provides stable isotopic composition data of the rainwater for the international GNIP database. 

In the meantime, she got to know the operation of the instrument used for δD and δ18O measurements (PICARRO L2130-i δD/δ18O Ultra High-Precision Isotopic Water Analyzer). During her two-week stay, she learned how to prepare water samples for the analysis and then she measured the δO and δD isotopic composition of her own samples with the help of Mia Tiljander. She also acquired knowledge of post-measurement calibration and data processing.

Each week had she meetings with other ENeRAG participants from the GTK (Nina Hendriksson, Kirsti Korkka-Niemi, Tiina Kaipainen and Mia Tiljander) in order to evaluate the results and understand the processes that lead to the characteristic isotopic composition of the water samples.

During this exchange, she deepened her knowledge in stable isotope geochemistry and she got a better understanding not only in the equilibrium and kinetic fractionation both at molecular and effective scales, but also in the assessment of processes leading to fractionation, especially diffusion, evaporation and condensation.

In the end, she was able to incorporate the results into a groundwater flow model that she built to support her hypothesis that explains the occurrence of high uranium activity in drinking water wells in her research area.