Efficacy of Halon-1301 as an age tracer - Multi-tracer evaluation in Shimabara springs

For sustainable use and management of local water resources, it is essential to clarify the groundwater flow system and its scale, and one of the effective methods is to estimate the residence time. One of the methods to clarify the residence time is to use "age tracers", which are mainly used for chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6) in Japan. Since each tracer has its own advantages and disadvantages, a combination of several tracers is necessary to improve the accuracy of the estimated residence time, and the development of new age tracers is required. Overseas studies such as Beyer et al. (2014) have begun to report the application of Halon-1301 as a new age tracer, but there are no such reports in Japan. Therefore, we evaluated the applicability of the Halon-1301 method in Japan by evaluating the residence time of five of the Shimabara springs in Shimabara City, Nagasaki Prefecture, using multiple age tracers.