A two-phase (water, gas)/three-component (water, salt, methane) model concept for flow and transport processes in a porous medium was developed. It accounts for density-driven flow as well as for mass transfer between the phases.Flow and transport processes around submarine groundwater springs were investigated with special emphasis on occuring gas bubbles. In the range of estimated parameters a reasonable agreement between simulations and measurements was obtained. Gas bubbles are probably caused by locally increased methane production or small-scale heterogenities. In the future, the model concept can be further developed to simulate non-isothermal multiphase/multicomponent processes, e.g., at gas hydrates.