Dating of young groundwater using four anthropogenic trace gases (SF₆, SF₅CF₃, CFC-12 and Halon-1301): methodology and first results^†

† Originally presented at the IAEA International Symposium on Isotope Hydrology: Revisiting Foundations and Exploring Frontiers, 11–15 May 2015, Vienna, Austria.

ABSTRACT

A dedicated, GC-based analytical system is presented which allows detection of four anthropogenic trace gases (SF₆, SF₅CF₃, CFC-12 and Halon-1301) in a single water sample, with detection limits and measurement uncertainties sufficiently low to employ them as quantitative indicators of groundwater age. The gases dissolved in water are extracted in the field using the method based on a dynamic head-space concept. In the laboratory, the investigated gases are cryogenically enriched, separated and measured using an electron capture detector. Reproducibility of the analyses is in the order of 2–5 %. The investigated tracers were measured in several production wells located in the recharge area of an intensively exploited aquifer in southern Poland. While the piston-flow ages of groundwater in the investigated wells revealed internal consistency, they appeared to be generally smaller than the ages derived from time series of tritium content in those wells, interpreted by lumped-parameter models. This difference stems mainly from significantly longer travel times of tritium through the unsaturated zone, when compared to the gaseous tracers being used. The results of this study highlight the benefits of using multiple tracing in quantifying timescales of groundwater flow in shallow aquifer systems.

KEYWORDS:

• Bromotrifluoromethane
• gaseous anthropogenic tracers
• groundwater dating
• hydrological modelling
• isotope hydrology
• sulphur hexafluoride
• SF₅CF₃
• tritium

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

† Originally presented at the IAEA International Symposium on Isotope Hydrology: Revisiting Foundations and Exploring Frontiers, 11–15 May 2015, Vienna, Austria.

Additional information

Funding

Financial support of this work through the funds of Polish Ministry of Science and Higher Education [research project N N525 362637 and the statutory funds of AGH University of Science and Technology] as well as the GENESIS project funded by the European Commission 7FP [contract 226536] is kindly acknowledged.