Effect of different sampling methods on concentrations of sulphur hexafluoride (SF<sub>6</sub>) in groundwater and age dating

TSUCHIHARA Takeo, OKUYAMA Takehiko, ISHIDA Satoshi, SHIRAHATA Katsushi

doi:10.5917/jagh.60.41

<p>Atmospheric concentrations of sulfur hexafluoride (SF₆) have continued to rise since the middle of the 20th century and therefore, it is necessary to prevent current atmospheric contamination into groundwater samples for use in age dating of groundwater. On the basis of SF₆ concentrations of groundwater at the same points collected by different sampling methods, this paper focuses on the influence of sampling methods on groundwater dating. Results obtained by using different six methods for water sampling show that inter-method uncertainty for groundwater dating is up to 1.7 years. However, the SF₆ concentration of groundwater sampled in contact with the atmosphere is not necessarily so high, and the influence of elution of SF₆ from sampling tools is not identified. Furthermore, the calculation of SF₆transfer from gas to liquid phase indicates that during sampling process using a well bailer, theoretical increase in SF₆ concentration of groundwater is less than 1 % corresponding to a residence time of 0.2 years. It is thus deduced that the uncertainty of groundwater dating is mainly due to the heterogeneity of pumped-up groundwater and there is a limited influence of contamination of SF₆ from the atmosphere associated with sampling methods on groundwater dating.</p>

Effect of different sampling methods on concentrations of sulphur hexafluoride (SF<sub>6</sub>) in groundwater and age dating

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