Monitoring of a Simulated CO<sub>2</sub> Leakage in a Shallow Aquifer Using Stable Carbon Isotopes SchulzAlexandra VogtCarsten LamertHendrik PeterAnita HeinrichBen DahmkeAndreas RichnowHans-Hermann 2012 Artificial carbon dioxide leakage into a shallow aquifer was monitored using stable carbon isotope measurements at a field site near the town of Wittstock, Brandenburg, Germany. Approximately 400 000 L of CO<sub>2</sub> were injected into a shallow aquifer at 18 m depth over 10 days. The <sup>13</sup>C/ <sup>12</sup>C ratios of the CO<sub>2</sub> were measured in both groundwater and soil gas samples to monitor the distribution of the injected CO<sub>2</sub> plume and to evaluate the feasibility and reliability of this approach to detect potential CO<sub>2</sub> leakage, for example from carbon capture and storage (CCS) sites. The isotopic composition of the injected CO<sub>2</sub> (δ<sup>13</sup>C −30.5 ‰) was differentiable from the background CO<sub>2</sub> (δ<sup>13</sup>C −21.9 ‰) and the artificial CO<sub>2</sub> plume was monitored over a period spanning more than 204 days. The results demonstrate that this stable isotope monitoring approach can be used to identify CO<sub>2</sub> sources and detect potential CO<sub>2</sub> migration from CCS sites into overlying shallow aquifers or even into the upper subsurface. A significant difference between the isotope ratios of the natural background and the injected CO<sub>2</sub> is required for this monitoring approach to be effective.