Leakage of CO2 from geological storage and its impacts on fresh soil-water systems: a review.

Leakage of CO2 from the geological storage is a serious issue for the sustainability of the receiving fresh soil-water systems. Subsurface water quality issues are no longer related to one type of pollution in many regions around the globe. Thus, an effort has been made to review studies performed to investigate supercritical CO2 (scCO2) and CO2 enrich brine migration and it's leakage from geological storage formations. Further, the study also reviewed it's impacts on fresh soil-water systems, soil microbes, and vegetation. The first part of the study discussed scCO2/CO2 enrich brine migration and its leakage from storage formations along with it's impact on pore dynamics of hydrological regimes. Later, a state-of-the-art literature survey has been performed to understand the role of CO2-brine leakage on groundwater dynamics and its quality along with soil microbes and plants. It is observed in the literature survey that most of the studies on CO2-brine migration in storage formations reported significant CO2-brine leakage due to over-pressurization through wells (injections and abandoned), fracture, and faults during CO2 injection. Thus, changes in the groundwater flow and water table dynamics can be the first impact of the CO2-brine leakage. Subsequently, three major alterations may also occur-(i) drop in pH of subsurface water, (ii) enhancement of organic compounds, and (iii) mobilization of metals and metalloids. Geochemical alteration depends on the amount of CO2 leaked and interactions with host rocks. Therefore, such alteration may significantly affect soil microbial dynamics and vegetation in and around CO2 leakage sites. In-depth analysis of the available literature fortifies that a proper subsurface characterization along with the bio-geochemical analysis is extremely important and should be mandatory to predict the more accurate risk of CO2 capture and storage activities on soil-water systems.