The numerous CO<sub>2</sub> reservoirs in the Colorado Plateau region of the United States are\ud natural analogues for potential geologic CO<sub>2</sub> sequestration repositories. To better\ud understand the risk of leakage from reservoirs used for long-term underground CO<sub>2</sub>\ud storage, we examine evidence for CO<sub>2</sub> migration along two normal faults from a\ud reservoir in east-central Utah. CO<sub>2</sub> -charged springs, geysers, and a hydrocarbon seep\ud are localised along these faults. These include natural springs that have been active for\ud long periods of time, and springs that were induced by recent drilling. The CO<sub>2</sub> -charged\ud spring waters have deposited travertine mounds and carbonate veins. The faults cut\ud siltstones, shales, and sandstones and the fault rocks are fine-grained, clay-rich gouge,\ud generally thought to be barriers to fluid flow. The geologic and geochemical data are\ud consistent with these faults being conduits for CO<sub>2</sub> to the surface. Consequently, the\ud injection of CO<sub>2</sub> into faulted geologic reservoirs, including faults with clay gouge, must\ud be carefully designed and monitored to avoid slow seepage or fast rupture to the\ud biosphere
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