HR: 0800h
AN: H21C-1354    [Abstracts]
TI: Methodology for Hydrogeological Characterization of faults: Experience at the Mizunami URL, Japan
AU: * Salden, W
EM: walter.salden@jnc.go.jp
AF: Research Fellow, Mizunami Underground Research Laboratory, Tono Geoscience Center, Japan Nuclear Cycle Development Institute, 1-64, Yamanouchi, Akeyo, Mizunami, Gifu, 509-6132 Japan
AU: Takeuchi, S
EM: takeuchi@tono.jnc.go.jp
AF: Mizunami Underground Research Laboratory, Tono Geoscience Center, Japan Nuclear Cycle Development Institute, 1-64, Yamanouchi, Akeyo, Mizunami, Gifu, 509-6132 Japan
AU: Fujita, Y
EM: fujita.yuuji@jnc.go.jp
AF: Mizunami Underground Research Laboratory, Tono Geoscience Center, Japan Nuclear Cycle Development Institute, 1-64, Yamanouchi, Akeyo, Mizunami, Gifu, 509-6132 Japan
AB: At the Mizunami Underground Research Laboratory (URL) construction site in central Japan, construction of two vertical shafts, each to a depth of 1000m, began in 2004. Prior to the start of construction, a comprehensive, multiphase surface-based and borehole-based testing program was carried out to characterize the undisturbed geological environment and to record changes resulting from construction. Several near-vertical faults that cross the URL site were identified using mapping and geophysical methods and their hydrogeological properties have been investigated using single, and multiple borehole well test methods. One fault in particular was identified by early mapping and has subsequently been shown to be a hydrogeologically significant groundwater flow barrier. Multi-level groundwater pressure monitoring data, which covers the pre-construction, well testing, and early construction phases are analyzed. These data show strongly differing pressure response behavior on opposing sides of the fault. Significantly, differing pressure responses due to large earthquakes, with recovery times lasting as long as approximately six months, were observed. By August 2005, construction of the two shafts reached a depth of approximately 150m and resulted in a complex pattern of piezometric level drawdown behavior. A maximum of approximately 50m change in the piezometric level on one side of the fault, and a much smaller (~1m) change on the opposite side of this fault was observed. In this study we show that analysis of multi-level piezometric pressure data can be a significant tool for hydrogeological characterization of faults in complex flow systems.
DE: 1829 Groundwater hydrology
DE: 1830 Groundwater/surface water interaction
DE: 1848 Monitoring networks
DE: 1895 Instruments and techniques: monitoring
SC: Hydrology [H]
MN: Fall Meeting 2005