Environmental Technology for Geological Storage of Carbon Dioxide
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Work Package # 3

Work Package 3: Environmental assessment of CO2 contamination in shallow aquifers: Team Leader Rasmus Jakobsen (DTU): participants Flemming Larsen (GEUS), Dieke Postma (GEUS) and Ph.D. Student Aaron Cahill (DTU).

If CO2 escapes from a storage site it will migrate upwards potentially entering aquifers used for drinking water supply. In itself, CO2 dissolved in water is not poisonous, bottled carbonized water contains similar amounts of CO2, but the added CO2 increases the acidity of the water. This will increase the rates of mineral dissolution in the sediments and the increased concentration of H+ and carbonate species may mobilize undesirable elements and compounds previously bound to the mineral surfaces.

The effects of these geochemical reactions could be mobilization of Ni, Pb and other trace metals competing with H+ for binding sites on the mineral surfaces and release of oxyanions like arsenate and arsenite, phosphate or selenate bound to mineral surfaces in exchange for carbonate species. Higher rates of mineral dissolution may release undesirable components more rapidly than in the undisturbed aquifer, resulting in concentrations exceeding drinking water standards. Dissolution may also lead to the formation of preferential flow paths, lowering transit times of any pollutant.

It is the main objective of this WP to investigate the effect that highly CO2 charged waters (PCO2 = 1-3 atm) and its interaction with the sediment may have on the groundwater composition. This will initially be investigated through a combination of batch and column test, using CO2 charged groundwater on a range of common aquifer sediments and observing the release of contaminants.

Subsequently, field tests in actual aquifer systems will be carried out. Push-pull tests, dipole tests, and natural gradient tests, all involving the injection of CO2 charged and tracer marked groundwater, and an analysis of the effects on groundwater quality and aquifer sediment characteristics, are under consideration. Column and field results will be modeled with reactive transport models considering mineral dissolution, ion exchange processes, surface complexation and redox processes, in order to obtain a quantitative understanding of the processes. The results of the field and laboratory experiments will be used for assessing impact scenarios through forward modeling of both physical and chemical responses to CO2, contamination.

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