> I would like to model heavy metals behaviour in soils and groundwater. > Do you think realistic representing the unsaturated zone by the gas-phase option and solid-solution? I think you probably want to model the gases as fixed partial pressures, which is done with EQUILIBRIUM_PHASES rather than GAS_PHASE. This is confusing, but the unsaturated zone is an open system, whereas the GAS_PHASE assumptions are for a closed system. As for solid solutions, equilibrium with individual minerals (EQUILIBRIUM_PHASES) is simpler and probably adequate. Unless you are working with a specific solid solution, you probably do not need the solid solution capability. > The last assumption would imply that the fluid is in equilibrium with the matrix which may not be true if water flows fastly. You will have to chose which minerals and gases are likely to remain in equilibrium. EXCHANGE and SURFACE are also equilibrium reactions. Other important reactions will be defined with REACTION or KINETICS, where KINETICS is more difficult to implement. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled
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