Groundwater quality effects of CO2 escaping from carbon storages (CO2-CS)

WP 3: If CO2 escapes from a storage and migrates up through the geological sequence, there is a risk of contaminating aquifers used for drinking water supply. In itself, CO2 dissolved in water is not poisonous, but adding CO2 to the water will increase the acidity of the water, causing mineral dissolution in the sediments and increased adsorption of carbonate species on the mineral surfaces. A decrease in groundwater pH may lead to the mobilization Ni and other trace metals (Kjøller et al), adsorption of carbonate species may displace other oxyanions like arsenate and arsenite, phosphate or selenate (Appelo et al 2002; CD-Music) bound to the sediment grains. Dissolution of minerals may release undesirable components into the groundwater and may lead to the formation of preferential flow paths, lowering transit times of any pollutant. It is the objective of this WP to investigate the effect that highly CO2 charged waters (PCO2 = 1 atm) and its interaction with the sediment may have on the groundwater composition. First a series of column experiments will be carried out with common aquifer sediments (non calcareous sand, calcareous sand and limestone), the sediments will be leached by CO2 charged groundwater in order to study the release of contaminants. Subsequently, push-pull tests in the aquifers will be carried out, by injecting and later retrieving CO2 charged and tracer marked groundwater (Assayag et al., 2009) and through water analysis identify the geochemical processes occurring. Repetitions will reveal whether the ongoing geochemical reactions are directly modifying the permeability/porosity of the rocks. Push-pull tests will be supplemented by a dipole test in a shallow aquifer. Sediment cores are taken before CO2 charged water is circulated through the aquifer while the geochemical effects are monitored in water samples. When circulation is stopped, new sediment cores will enable direct studies of the effects on the sediment. Column and field results will be modelled with reactive transport models considering mineral dissolution, redox processes and surface complexation in order to obtain a quantitative understanding of the problems involved.