Japan Geoscience Union Meeting 2016

Presentation information


Symbol A (Atmospheric and Hydrospheric Sciences) » A-HW Hydrology & Water Environment

[A-HW18] Isotope Hydrology 2016

Wed. May 25, 2016 9:00 AM - 10:30 AM 202 (2F)

Convener:*Masaya Yasuhara(Rissho Univ.), Kohei Kazahaya(Geological Survey of Japan, AIST), Kazuyoshi Asai(Geo Science Laboratory), Shinji Ohsawa(Institute for Geothermal Sciences, Graduate School of Science, Kyoto University), Futaba Kazama(Social Cystem Engineering, Division of Engineering, Interdiciplinary Graduate School of Medical and Engineering, University of Yamanashi), Masaaki Takahashi(The National Institute of Advanced Industrial Science and Technology), YUICHI SUZUKI(Faculty of Geo-Environmental Sience,Rissho University), Chair:Masaya Yasuhara(Rissho Univ.)

10:15 AM - 10:30 AM

[AHW18-05] Groundwater age determination by using 85Kr in groundwater at the Kakitagawa spring water in Mt. Fuji spring discharge area

*Makoto Kagabu1, Midori Matsunaga3, Masahiko Ono2, Isao Machida2, Reo Ikawa2, Jun Shimada3, Noriyuki Momoshima4 (1.Graduate School of Fisheries and Environmental Sciences, Nagasaki University, 2.National Institute of Advanced Industrial Science and Technology, 3.Graduate School of Science and Technology, Kumamoto University, 4.Radioisotope Center, Kyushu University)

Keywords:Krypton-85, Groundwater age dating, Kakitagawa spring water

Groundwater age dating study around Mt. Fuji area have been conducted by several researches (Ochiai, 1970; Yoshioka et al., 1993; Mahara et al., 1993; Asai and Tsujimura, 2010; Tosaki et al., 2011; Ohta et al., 2012). Various methods were adopted in Mt. Fuji spring discharge area such as 3H, noble gases, CFCs, 36Cl/Cl and 228Ra/226Ra activity. All results show relatively young age (0 to several decades) in the Mt. Fuji groundwater, except for CFCs method which affected local anthropogenic source (Asai and Tsujimura, 2010). However, the result in each method contains the “uncertainty” of its age. Unlike these methods, Krypton 85 (85Kr) has high resolution for the age estimation, hence we conducted age determination at the Kakitagawa spring water located in the southeastern part of Mt. Fuji. Krypton 85 (85Kr) is a man-made trace gas from reprocessing plant origin whose atmospheric concentrations have been increasing over the past few decades. As it is soluble in water, it can be used as groundwater age indicators over timescales ranging from a few years to a few decades. 85Kr specific activities in groundwater was 1.022 ± 0.028 Bq/m3, and the estimated age were 5.2 ± 0.4 years. This young age is corresponding to the previous studies, additionally the range of the estimated age by 85Kr was much smaller compare to other methods. Furthermore, 85Kr method shows the strong advantage against the anthropogenic contamination.