Numerical investigation for the impact of CO 2 geologic sequestration on regional groundwater flow Hajime Yamamoto a , Keni Zhang b , Kenzi Karasaki b , Atsunao Marui c , Hitoshi Uehara d , and Noriaki Nishikawa d a Taisei Corporation, 344-1 Nase-cho Totsuka-ku, Yokohama 245-0051, Japan Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA c National Institute of Advanced Industrial Science and Technology, 1-1-1, #7 Higashi, Tsukuba 305-8567, Japan d Japan Agency for Marine-Earth Science and Technology, 3173-25 Showa-machi Kanagawa-ku, Yokohama 236-0001, Japan b Abstract Large-scale storage of carbon dioxide in saline aquifers may cause considerable pressure perturbation and brine migration in the deep formations, which may give rise to a significant influence on the regional groundwater system. With the help of parallel computing techniques, a comprehensive, large-scale numerical simulation of CO 2 geologic storage that predicts not only CO 2 migration but also its impact on regional groundwater flow was performed. As a case study, a hypothetical industrial-scale CO 2 injection in the Tokyo Bay, which is surrounded by the most industrialized area in Japan, was considered, and the impact of down-dip CO 2 injection on up-dip near-surface aquifers was investigated. A regional hydrogeological model with an area of about 60km×70km around the Tokyo Bay was discretized into about 10 million gridblocks. To solve the high-resolution model efficiently, we used a parallelized multiphase flow simulator TOUGH2-MP/ECO2N on a world-class high performance supercomputer in Japan, the Earth Simulator. In the simulation, CO 2 was injected into a storage aquifer at about 1km depths under the Tokyo bay from 10 wells with the total rate of 10 million tons/year for 100 years. Through the model, regional groundwater pressure build-up and seepage changes at land surface are examined. The results suggest that even if containment of CO 2 plume is ensured, pressure buildup in the order of tens of meters can occur in shallow confined layers of extensive regions including urban inlands. Keywords: CO 2 storage; parallel computation, large-scale simulation; groundwater pressure; Tokyo Bay; Kanto Plain; Earth Simulator 1. Introduction It is believed that the greenhouse gas may cause global climate change. One of the proposed approaches for reducing the greenhouse gas content in the atmosphere is through capturing CO 2 from large emission sources and injecting it into deep saline