On mobilization of lead and arsenic in groundwater in response to CO2 leakage fromdeep geological storage

摘要

If carbon dioxide stored in deep saline aquifers were to leak into an overlying aquifer containing potablegroundwater, the intruding CO_2would change the geochemical conditions and cause secondary effectsmainly induced by changes in pH. In particular, hazardous trace elements such as lead and arsenic, which arepresent in the aquifer host rock, could be mobilized. In an effort to evaluate the potential risks to potablewater quality, reactive transport simulations were conducted to evaluate to what extent and mechanismsthrough which lead and arsenic might be mobilized by intrusion of CO_2. An earlier geochemical evaluation ofmore than 38,000 groundwater quality analyses from aquifers throughout the United States and anassociated literature review provided the basis for setting up a reactive transport model and examining itssensitivity to model variation. The evaluation included identification of potential mineral hosts containinghazardous trace elements, characterization of the modal bulk mineralogy for an arenaceous aquifer, andaugmentation of the required thermodynamic data. The reactive transport simulations suggest that CO2ingress into a shallow aquifer can mobilize significant lead and arsenic, contaminating the groundwater nearthe location of intrusion and further downstream. Although substantial increases in aqueous concentrationsare predicted compared to the background values, the maximum permitted concentration for arsenic indrinking water was exceeded in only a few cases, whereas that for lead was never exceeded.