Intrusion of CO2 and impurities in a freshwater aquifer — Impact evaluation by reactive transport modelling
Résumé
Contamination of fresh groundwater is one of the environmental issues of Carbon Capture and Storage. We simulate with the reactive transport code TOUGHREACT the intrusion of CO 2 +impurities from oxycombustion capture in a freshwater aquifer model based on a glauconitic sandstone aquifer. We choose an unfavorable scenario where the contaminant gas presents maximal contents in SO x , NO x and O 2. Water quality changes after a 10 years intrusion are exposed. French quality standards in pH, Fe, Mn and sulphates concentrations for drinking water are reminded in the results for reference. Acidification and carbonation of water induces Fe-and Mn-bearing minerals dissolution that increases the concentration of these metals in water. Contamination by sulphates is due to the SO 2 oxidation by O 2 , both of these components being carried by the contaminant gas. The vertical extent of contamination is enhanced by both the upward migration of gaseous CO 2 and downward migration of dense carbonated water. The presence of SO 2 and NO in the contaminant gas, even in very low concentrations, induces a negative local pH shift of 1 unit by comparison with a pure-CO 2 contaminant gas. This pH shift has consequences on Fe and Mn release amplitude. The code does not allow realistic modelling of the fate of NO x in the aquifer. But we hypothesize this component to be oxidized by O 2 into nitrite or nitrates (health-significant substances) that persist into the aquifer. Perspectives are addressed.