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Methods for using argon-39 to age-date groundwater using ultra-low-background proportional counting
Emily Mace1, Craig Aalseth1, Jill Brandenberger1
1Pacific Northwest National Laboratory, P.O. Box 999, MSIN J4-65, Richland, WA 99352, USA.
Summary
Argon-39 is a new tracer for dating groundwater between 50 and 1,000 years old. This method helps fill a crucial age gap, improving our understanding of groundwater systems.
Area of Science:
- Geochemistry
- Hydrology
- Isotope Science
Background:
- Argon-39 (39Ar) is a naturally occurring isotope with a half-life of 269 years.
- It is useful for dating environmental archives like glaciers and oceans.
- Existing groundwater tracers have limitations in covering intermediate age ranges.
Purpose of the Study:
- To introduce and validate Argon-39 as a novel tracer for groundwater age-dating.
- To address the gap in dating groundwater between 50 and 1,000 years.
Main Methods:
- Degassing argon from groundwater samples.
- Measuring 39Ar concentrations using mass spectrometry.
- Calculating groundwater age based on 39Ar decay.
Main Results:
- 39Ar effectively quanties groundwater age within the 50-1,000 year range.
- The method provides a valuable addition to the suite of groundwater dating tools.
Conclusions:
- Argon-39 is a viable and important tracer for intermediate-aged groundwater.
- Its application enhances the understanding of groundwater recharge and flow dynamics.
