Isotope methods in groundwater studies

In hydrogeological studies the water types of different end-members are of special interest, since most groundwaters are mixtures of different end-member types. Using a combination of different isotope methods the nature of water-rock interactions and the participation of different end-member water types in mixing and water evolution processes can be studied in detail (Négrel et al. 2005). It is also advisable to combine several isotopes in hydrogeological studies, when possible (IAEA 1998). As an example, measuring both δ³⁴S and δ¹⁸O from sulphates derives in more detailed information about the sources of sulphur than only relying on sulphur isotopic composition (e.g. Clark & Fritz 1997). Integration of conventional hydrochemistry with isotopes is also essential, because elemental concentrations could help in interpretation of contaminant sources and groundwater pathways (IAEA 1998).

In the following pages use and applications of isotope methods are discussed in a more detail:

• Lead isotopes
• Oxygen and hydrogen isotopes
• Strontium isotopes
• Sulphur isotopes
• Uranium isotopes

In addition, in Closedure project use of H, O, S, U, and Sr isotopes was applied in a study to recognize impacts of mining on natural waters and in identifying groundwater flow paths in bedrock structures:

• Monitoring of mining impact on natural waters using isotopic tracers (S, U, and Sr) – a pilot study from Talvivaara, northeastern Finland
• Use of H and O stable isotopes in recognition of preferable groundwater flow paths in bedrock fracture zones

References

Clark, I.D. & Fritz, P. 1997. Environmental Isotopes in Hydrogeology. Lewis Publishers, Boca Raton, 328 p.

IAEA. 1998. Application of isotope techniques to investigate groundwater pollution. IAEA-TECDOC-1046, 7-8.

Négrel, P., Casanova, J. & Blomqvist, R. 2005. ⁸⁷Sr/⁸⁶Sr of brines from the Fennoscandian Shield: a synthesis of groundwater isotopic data from the Baltic Sea region. Canadian Journal of Earth Sciences 42, 273-285.