Arsenic Enrichment in Groundwater Aquifers over Geological Carbon Storage Sites: A Potential Concern

Social acceptance of geological CO₂ storage faces a significant barrier from the risk that unexpected leakage through fractures or faults may contaminate potable groundwater via arsenic (As) mobilization and enrichment. Utilizing reactive transport modeling, we demonstrate that CO₂ leakage can markedly decrease the pH and thus elevate As concentrations downstream of the leakage point, primarily due to As desorption from adsorbents under acidified conditions. Results indicate that the extent of pH decrease and As enrichment is significantly attenuated in aquifers abundant in adsorption sites. Furthermore, we demonstrate that arsenic mobilization is redox-dependent, as the reduction of As(V) to As(III) under favorable conditions leads to arsenic scavenging, driven by the superior adsorption affinity of As(III) on aquifer minerals. Our findings highlight the critical importance of thoroughly characterizing both adsorption site density and redox potential to accurately assess the risks of CO₂ leakage-induced arsenic contamination in groundwater systems. The identified geochemical controls provide a valuable reference for predictive modeling of As enrichment in carbon sequestration projects.