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Re: question

> 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 Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

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