The use of environmental tracers to characterize a leaky CO2 CCS natural analogue site, Soda Springs, Idaho, USA

Large‐scale global adoption of carbon capture and storage (CCS) as a means of minimizing atmospheric CO2 emissions requires an unprecedented effort to store gigatons of anthropogenic emissions in the earth's subsurface. Critical to the adoption and ultimate success of CCS is the protection of valuable water resources that may be impacted by leaking CO2 from CCS operations. Therefore, appropriate technical tools and societal controls will need to be developed and evaluated to maximize the atmospheric benefits of CCS while limiting potential deleterious effects of its implementation. Here, we utilize a naturally leaking CO2 system located at Soda Springs, Idaho, USA, as an analogue for industrial‐scale CCS deployment. This site is particularly relevant and useful for studying the consequences of CCS because it allows the examination of geologic systems at temporal and spatial scales not accessible by laboratory and field experiments. The Soda Springs system is an ideal CCS natural analogue site with the source of CO2 occurring at depths and temperatures expected for large‐scale CCS systems. Soda Springs also provides long‐term examples of at least three potential failure modes for CCS systems, including direct migration of CO2 charged brine to the surface via faulting or wells, upward movement of CO2 from the injection‐horizon into over lying shallow aquifers, and the displacement of reservoir brine into shallower aquifers. These failure mechanisms were differentiated and characterized utilizing variations in water chemistry including rare earth elements providing a framework for delineating the movement of CO2‐influenced fluids migrating from deep CCS reservoirs into overlying aquifers. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.