Evaluation of Influence of Splay Fault Growth on Groundwater Flow around Geological Disposal System

In geological disposal, the direct effect of active faults on geological repositories is avoided at the stage of site characterization; however, uncertainty remains for the avoidance of faults derived from active faults, which are concealed deep under the ground and are dif fi cult to detect by site investigation. In this research, the in fl uence of the growth of undetected splay faults on a natural barrier in a geological disposal system due to the future action of faults was evaluated. We investigated examples of splay faults in Japan and set conditions for the growth of splay faults. Furthermore, we assumed a disposal site composed of sedimentary rock and made a hydrogeological model of the growth of splay faults. We carried out groundwater fl ow analyses, changing parameters such as the location and depth of the repository and the growth velocity of splay faults. The results indicate that the main fl ow path from the repository is changed into an upward fl ow along the splay fault due to its growth and that the average velocity to the ground surface becomes one or two orders of magnitude higher than that before its growth. The results also suggest that splay fault growth leads to the possibility of the downward fl ow of oxidizing groundwater from the ground surface area.