3:15 PM - 3:30 PM
[AHW27-19] Groundwater dating in southern Hamadori region, Fukushima, Japan
Keywords:groundwater, residence time, tritium, sulfur hexafluoride, Fukushima, The Great East Japan Earthquake
Study area was Iwaki and Hirono in the southern Hamadori region. Groundwater samples were collected at 39 wells in Iwaki and 27 wells in Hirono. SF6 was detected at all wells except for one well, and exceptionally high SF6 concentrations were measured at four wells. These exceptionally high SF6 concentrations were presumably caused by local source contamination because such concentrations cannot be explained from equilibrium between groundwater and modern air. Considering that SF6 was industrially produced after 1953 (Maiss and Brenninkmeijer, 1998), the results imply that groundwater from the almost all wells contain fraction recharged after 1953, at least partly. 25 percentile of residence time assuming piston flow was 18.9 years, median was 21.8 years, and 75 percentile was 26.8 years. Analytical results of tritium are compared with SF6 based on lumped parameter models (Zuber and Maloszewski, 2001), and regional characteristics of the estimated residence times are shown in the presentation.
Maiss M. and C. A. M. Brenninkmeijer, 1998, Atmospheric SF6: Trends, sources, and prospects, Environmental Science and Technology, 32, 3077-3086.
Muto Y., K. Kashiwaya, T. Kubo, K. Koike, S. Yabusaki, N. Shibasaki, R. Ikawa, A. Marui, 2013, Groundwater systems in Hirono region indicated from geochemical characteristics of groundwater, Abstracts of Japanese Association of Groundwater Hydrology 2013 fall meeting, 204-209.
Zuber A. and P. Maloszewski, 2001, Lumped parameter models, in: Mook, W.G. (Ed.), Environmental Isotopes in the Hydrological Cycle, Vol. VI. UNESCO, Paris, 5-35.