Heavy Metal Pollution to Shallow Groundwater Aquifer Caused by CO ₂ Leakage During Geological Carbon Storage (GCS)

Abstract In the context of geological carbon storage, assessing the geochemical alteration of groundwater in shallow aquifers due to unintended leakage from deep reservoirs is crucial. Elevated levels can cause groundwater acidification and potential release of heavy metal from the aquifer rock to groundwater. In this study, we aim to elucidate the mechanism behind heavy metal release and discuss the selection of geochemical markers for detecting leakage in aquifers with varying geochemical and hydrogeological characteristics. Reactive transport simulations were conducted using a Matlab reservoir simulation toolbox, which was validated against a field test for leakage. Results indicate that while carbonate‐rich aquifers exhibit a continuous release of heavy metals governed by rapidly dissolving impure carbonates, carbonate‐poor aquifers show a more pronounced concentration shift of heavy metals controlled by surface complexation processes. Nevertheless, we find that dissolved inorganic carbon and pH can be used as general geochemical indicators for exposure, regardless of the carbonate content in the aquifer rock. Most of the selected elements exceed or approach the maximum admissible levels for drinking water following the intrusion of ‐rich water. Upon detection and cessation of the leakage source, all elements in the affected area revert to their initial levels under the natural flushing of groundwater flow, with the rate of self‐remediation increasing in response to the hydraulic gradient.