Reactive transport modeling of arsenic mobilization in shallow groundwater: impacts of CO2 and brine leakage

Abstract

Carbon dioxide (CO2) and saline water leakage from deep sequestration reservoirs to overlying shallow drinking water aquifers is a major concern for geologic CO2 sequestration. In this study, a field-scale reactive transport model of a natural CO2 analog, the Chimayo site in New Mexico, was created to quantify water–rock–CO2 interactions and arsenic (As) mobilization responses to CO2 and saline water leakage. This study provides analyses and forecasts of the site following field observations of hydrogeological and geochemical data, and integrated calculations with combined batch experiments and reactive transport simulations of geochemical reaction kinetic parameters. The results of this study suggest that: (1) with the regional groundwater flow of 1% hydraulic gradient, the leakage of CO2 could reach to 3000 m downstream in 1000-year time scale; (2) clay minerals of the aquifer show a strong capacity to mitigate As mobilization with adsorption reactions, and within 1000-year simulation time, the aquifer sediments stabilize almost 100% leaked As; (3) the deeper brackish water is the source of As contamination of the Chimayo groundwater, and As concentration increase only appears along the fault.