Impact of natural and local anthropogenic SF6 sources on dating springs and groundwater using SF6 in central Japan

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Sulfur hexafluoride (SF6) concentrations in springs and groundwater were measured in the Chubu region of central Japan to evaluate the impact of natural and local anthropogenic SF6 and the validity of SF6 for dating young groundwater in Japan. Sampled water showed detectable concentrations of SF6 at 0.21–125 f mol/L. Most of the mountain springs have SF6 concentration assumed by the dissolution of the clean ambient air in Northern hemisphere. The SF6-based apparent ages for the mountainous springs were estimated at less than 6 years in smaller catchment areas (< 0.5 km2), and ranged from 4 to 32 years in the larger catchment areas located on the Quaternary volcanoes. The SF6 ages for mountain springs were consistent with the scale of groundwater flow and with previously determined 3H ages for groundwater in similar settings in Japan, suggesting the loading of natural SF6 in the groundwater is relatively small in the mountainous areas. In the plains, local industrial activities led to high concentrations of SF6 in some of the analyzed groundwater. The results suggest SF6 can be an effective dating tool for young groundwater in Japan, when and where the input of local anthropogenic SF6 is negligible.