Monitoring of a Simulated CO₂ Leakage in a Shallow Aquifer Using Stable Carbon Isotopes

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 CO₂ were injected into a shallow aquifer at 18 m depth over 10 days. The ¹³C/ ¹²C ratios of the CO₂ were measured in both groundwater and soil gas samples to monitor the distribution of the injected CO₂ plume and to evaluate the feasibility and reliability of this approach to detect potential CO₂ leakage, for example from carbon capture and storage (CCS) sites. The isotopic composition of the injected CO₂ (δ¹³C −30.5 ‰) was differentiable from the background CO₂ (δ¹³C −21.9 ‰) and the artificial CO₂ 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 CO₂ sources and detect potential CO₂ 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 CO₂ is required for this monitoring approach to be effective.