CO₂-shallow groundwater interaction and related hydrogeochemical mechanisms: A review on reduced-scale CO2 release field experiments

Carbon capture and storage (CCS) has been highlighted as a crucial technology for reducing carbon emissions, yet CO₂ leakage from the reservoir is still a matter of great public concern, especially because of water pollution reasons. Hence, reduced-scale CO₂ release experiments have been conducted worldwide to study hydrogeochemical response in shallow groundwaters. Although other reviews have been previously published, this study reviews critical data to establish a geochemical process-based framework of the scientific findings. Following this, four mechanisms were found to be responsible for hydrogeochemical behavior: (i) ion exchange is mainly responsible for short-lived increase in Mg, Ca, Ba and Sr concentrations; (ii) sorption and desorption processes were related to heavy metal and trace element variations, seemingly due to the presence of oxyhydroxides and clay minerals; (iii) silicate and carbonate dissolution played different roles as a function of specific aquifer mineralogy, releasing metals or influencing divalent cations response; (iv) conservative, mixing and oxidation processes were pointed out as possible mechanisms regulating variations of Cl⁻, SO₄²⁻ and NO₃⁻. Although studies suggested no parameter exceeded potable limits, most experiments were short-lived, possibly overlooking the CO₂ leakage response in a long-term exposure. Hence, further work is still needed specially to support relevant environmental legislation. © 2023 Society of Chemical Industry and John Wiley & Sons, Ltd.