Potential impacts of leakage from CO2 geological storage on geochemical processes controlling fresh groundwater quality: A review

Leakage of CO2 or brine coming from CO2 geological storage sites constitutes a risk for overlying fresh groundwater resources. One of the main risks is the potential alteration of groundwater quality by the intrusion of contaminants such as trace elements. This paper reviews studies that address the potential impacts of CO2 geological storage leakage on fresh groundwater quality. Leakage can directly modify the chemical properties of fresh water (pH, redox potential, chemical composition) and, as a result, indirectly modify the effect of biogeochemical processes controlling trace element availability. The ability of a CO2 or brine leak to introduce or mobilize trace elements and potentially degrade the quality of water in an overlying aquifer depends on the composition and quantity of the leaking fluids, the nature of the solid phases making up the aquifer (buffering and scavenging capacity) and the concentrations of undesirable or toxic elements that can be mobilized following any such modification. Furthermore, hydrogeological conditions will control the potential dissemination into groundwater. To date, studies have shown that trace elements can be significantly mobilized without necessarily exceeding quality thresholds. In a few cases where aquifers are naturally rich in trace elements (i.e. whose natural concentrations in groundwater are already high), CO2 is able to mobilize these trace elements (e.g. Fe, Mn, Ni, As, Ba, U) and increase concentrations up to or exceeding threshold values. This literature review provides a return on experience essential for both assessing biogeochemical risks prior to the installation of future CO2 geological storage sites and designing and installing fresh groundwater quality monitoring networks. (C) 2014 Elsevier Ltd. All rights reserved.