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

  • TSUCHIHARA Takeo
    National Agriculture and Food Research Organization, Institute for Rural Engineering
  • OKUYAMA Takehiko
    Faculty of Agriculture, Yamagata University
  • ISHIDA Satoshi
    National Agriculture and Food Research Organization, Institute for Rural Engineering
  • SHIRAHATA Katsushi
    National Agriculture and Food Research Organization, Institute for Rural Engineering

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Other Title
  • 採水方法が地下水の六フッ化硫黄濃度・地下水年代推定に及ぼす影響
  • サイスイ ホウホウ ガ チカスイ ノ ロクフッカ イオウ ノウド ・ チカスイ ネンダイ スイテイ ニ オヨボス エイキョウ

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Abstract

<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 SF6 transfer 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>

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