MT3DMS

[Mat]

Hello to everybody!

I began to use MT3DMS in ModelMuse, but I don't understand in which way I can impose a concentration flux as BC and not a constant concentration.
I tried to use WELL and SSM packages, but I don't understand the value of concentration shown in .mls file.
Could someone help me?
Thanks in advance

[Richard B. Winston]

If you make your boundary a mass-loading boundary, the value you specify
will be the mass per unit time that enters the groundwater system at
that location. For example, you could create a point object and in the
Object Properties dialog box you would go to the MODFLOW Features tab.
There you would check the check box for the SSM package. Next, check the
Mass-loading check box and specify the starting and ending times for the
boundary as well as the mass loading rates in units of mass/time. You
would not check the check box for the Well or any other MODFLOW stress
package in the Object Properties dialog box for this object. If you
don't check the mass-loading check box and check the check box for the
well package, the concentration that you specify will be the
concentration of the water that is injected into the aquifer from that
well. If the well extracts water instead of injecting it, the
concentration in the aquifer will be unaffected by the well.

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[Mat]

Thank you Richard, I followed your suggestion but I have another doubt: I imposed a value of mass loading in g/d, and I thought that in the first step (1 day) I would have the same set value, because my IC as concentration is null. This doesn't happen, but I have a value very very small respect to the mass loading imposed.....Can you help me? Can be a problem in the time step setting or in choice of solver?

[Richard B. Winston]

Did you remember to convert the units? The units of the mass flux are
mass per unit time (M/T) whereas the units of concentration are mass per
unit volume (M/L^3) so to convert the units, you must multiply the mass
flux by the time step length and divide by the cell volume. Assuming
that the movement of solute out of the cell is negligible, that would be
your expected concentration in the cell.