Revisiting the salt dome problem: new insights with the salt dissolution and pollutant release induced processes
Résumé
The salt dome problem is a well-known hydro geochemical challenge for density dependent flow and transport model-ing. The hydrogeologists community, consider generally the salt rock as impervious. In reality, and even with its very low permeability, a water flow and salt transport inside the rock could be significant at large geological time scale. We use a coupled model of flow, transport and geochemistry dealing with high concentrations, to simulate the coupled processes in the HYDROCOIN 4 classical problem to quantify these dissolution processes and their impact on the buried waste transport to the biosphere at large time scales. We quantify the time evolution of the rock porosity of the dome as well as the quantities of salt dissolved. We show that the porosity of the top band of the dome increases by a factor of 4.5 after 10 000 years. For the same duration, the top layer of the dome lost 50% of its salt mass. The amount of salt lost is not constant over time and the process of dissolution stabilizes after 8000 years keeping a constant rate of dissolution of 9.4 kg / year. A pollutant solute that migrates from the center of the dome, where waste burial facilities may have been stored, will reach the surface after 2200 years. We conclude that the salt dome is not impermeable and that the risk of migration of a pollutant through the dome is considerable.
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