The Effect a Recharge Type on the Calcite Dissolation and Porosity Enhancement in Fresh Water lens of Carbonate Coastal aquifer

When two solutions are mixed, concentrations in the mixture are volume-weighted averages of the two end-members, but the thermodynamic activities of the species controlling the water–mineral reactions are non-linear functions of the mixing ratio. Therefore, two end member solutions in equilibrium with carbonate phase could lead to a mixture undersaturated with respect to carbonate. A favorite place for this phenomenon is water table, where mixing of different waters is taking place. In this paper, Porosity change in freshwater lens of an island was calculated by coupling dissolution potential with a variable density flow and solute transport model. The effect of permeability enhancement on the rate of porosity change was evaluated. Dissolution due to this mixing takes place in water table and active edge of freshwater lens (40m from coastline). The results indicate an increase rate of 0.6×10-3 percent of porosity per year. Permeability enhancement increases the rate of dissolution and porosity change in fresh water lens.