HR: 0800h
AN: H11D-1293    [Abstracts]
TI: Long-term Geochemical Transport Simulation to Evaluate Ambient Chemical Conditions at Horonobe URL Site, Hokkaido, Japan
AU: * Yamamoto, H
EM: hajime.yamamoto@sakura.taisei.co.jp
AF: Taisei Corporation, 344-1 Nase-cho Totsuka-ku, Yokohama, 245-0051 Japan
AU: Shimo, M
EM: michito.shimo@sakura.taisei.co.jp
AF: Taisei Corporation, 344-1 Nase-cho Totsuka-ku, Yokohama, 245-0051 Japan
AU: Fujiwara, Y
EM: yasushi.fujiwara@sakura.taisei.co.jp
AF: Taisei Corporation, 344-1 Nase-cho Totsuka-ku, Yokohama, 245-0051 Japan
AU: Kunimaru, T
EM: kunimaru@hq.jnc.go.jp
AF: Japan Nuclear Cycle Development Institute, Miyazono-machi 1-8, Horonobe, Hokkaido, 098-3207 Japan
AU: Xu, T
EM: tianfu_xu@lbl.gov
AF: Lawrence Berkeley National Laboratory, One Cyclotron Road. MS:90-1116, Berkeley, CA 94720 United States
AU: Laaksoharju, M
EM: marcus@geopoint.se
AF: Geopoint AB, Fridshyddev. 15, Sollentuna, S-19136 Sweden
AB: JNC (Japan Nuclear Cycle Development Institute) has been planning an underground research laboratory (URL) in Horonobe, northern Hokkaido, Japan. In this study, long-term evolution of groundwater chemistry was simulated to evaluate ambient chemical conditions around the Horonobe URL site. The study area is about 8km by 4km and 2km deep region centered on the URL, in which the geology mainly consists of Pliocene diatomaceous argillaceous formations. Hydro-geochemical investigations using deep boreholes in about 3km by 3km area have suggested that groundwater chemistry around the site has been formed through the mixing of shallow fresh water and deep saline water. The deep groundwater has high salinity and differs from the present seawater in that it is highly reduced and has low pH, high bicarbonate and low magnesium concentration. Prior to the simulation, a computer code M3 (Laaksoharju et al. 1999) was used to model that the groundwater composition is affected by a two end-member mixing system. Next, the simulation of chemical changes during the intrusion of fresh water from land surface into deep saline water in the past 0.1 Ma was performed. A non-isothermal multiphase reactive geochemical transport simulation code TOUGHREACT (Xu and Press, 2001) was employed to solve the complex interplay of mass transport and chemical reaction in groundwater such as mineral dissolution/precipitation and ion exchange. The simulator was applied to a site-scale 3D geological structure model in which surface topography, the structures of geologic formations and a major fault were embedded. The results suggest that: 1) the spatial patterns of salinity and major constituents observed are in the site are generally consistent with a scenario of the intrusion of the surface fresh water into the deep saline water; 2) freshening of the deep saline water increases pH by cation exchange; 3) redox front migrates as oxidized water infiltrates from surface but is strongly buffered by reducing minerals such as pyrite.
DE: 1830 Groundwater/surface water interaction
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: Fall Meeting 2005