Dissolved trace elements dynamics during a rich-CO2-water leakage in a near-surface carbonate freshwater aquifer

Abstract

An experimental leak “simulation” was carried out at the Saint-Emilion experimental site (France). A volume of 200 L of CO2-rich water was injected into the shallow carbonated aquifer during low water table periods. One injection well and seven monitoring wells were equipped with either CO2 probes or multi-parameters probes to follow the plume.After the CO2-rich water injection, dissolved CO2 and electrical conductivity increased as the pH values decreased, highlighting the calcite dissolution. The calcite dissolution and desorption of iron oxides led to the migration of trace elements in the aqueous phase. As, V, Mo Cu, Ga, Co, Fe, and Cd showed a rapid increase in their concentrations. Mn, Sr, Li and Se showed the same evolution but with a temporal offset. The concentrations of some of these elements increased a second time several hours after the injection. Ba and Pb showed a major decrease immediately after injection, but Ba showed two peaks several hours after the injection. Zn and Si seemed to not be affected by the CO2 injection.Only As, Ba, and Se exceeded WHO/UE drinking water standards for a period of few hours. The global return to initial conditions was fast, showing the great resilience and the high buffering capacity of carbonate aquifers.