Re: Question about PHAST

[Angus Calderhead <acalderhead@xxxxxxxxxx>]

Thanks for that.
You supplied me with some helpful information.
Even with the corrections you suggested i am still getting some
discrepancies, mainly to do with the species concentrations.
The problem might be the MIN3P file.

Thanks again for your help,

Angus Calderhead

----- Original Message -----
From: "David L Parkhurst" <dlpark@xxxxxxxx>
To: "Angus Calderhead" <acalderhead@xxxxxxxxxx>
Sent: Monday, June 02, 2003 6:20 AM
Subject: Re: Question about PHAST


>
> I see a couple inconsistencies in the input files, but they both look
> wrong. So I'm not exactly sure what the problem is.
>
> (1) the units are slightly different between the PHAST chem file and the
> PHREEQC file, mol/kgw and mol/L, which should not make a significant
> difference, and the concentrations are slightly different. Still, the
> results should be pretty similar.
>
> (2) I think the problem is that you have defined 0 moles of calcite in
> equilibrium_phases 2 in the PHAST run. The moles of a mineral in
> EQUILIBRIUM_PHASES defaults to 10 moles. Thus
>
> Calcite 0 indicates 10 moles of calcite (PHREEQC file), whereas
> Calcite 0 0 indicates 0 moles of calcite are present (PHAST chem file).
>
> Water 2 in the PHAST file should dissolve both calcite and dolomite, but
> there is no calcite to dissolve in the PHAST run. The PHREEQC run has both
> calcite and dolomite present to react with initial solutions 1-100. This
is
> the fundamental reason for the discrepancies between the two runs.
>
> (3) EQUILIBRIUM_PHASES 0 has no function in the PHREEQC calculation
because
> the result of equilibrating solution 1 with calcite (10 moles) is not
> saved. The following couple of additional statements may be appropriate
for
> the PHREEQC file, I'm not sure. You explicitly equilibrate with
> equilibrium_phases 1 in the PHAST file, but there is no calcite to
> dissolve. It looks to me like you wanted the infilling solution to be in
> equilibrium with calcite, but this is not the case in the PHAST run
> (because there is no calcite) nor the PHREEQC run (because the result is
> not saved).
>
> SOLUTION 0
>     temp       25
>     pe         4
>     redox      pe
>     units      mol/kgw
>     density    1
>     H(0)       1.1e-7
>     Ca         0.0042
>     Cl         0.00024
>     Na         9.9e-005
>     Mg         7.12e-005
>     C(4)       5.5e-005
>     S(6)       0.00415
>     water      100
>
> EQUILIBRIUM_PHASES 0
>     Calcite   0
>
> # You should add the following two lines if you want to save SOLUTION 0
> after it has equilibrated with calcite
>
> SAVE solution 0
> END
>
> (3) The phreeqc file specifies 100 kg water, whereas phast uses 1 kg
water.
> This makes a difference in the ratio of dolomite and calcite that are
> present. In one case it is 0 calcite and 13.9 dolomite mole per kilogram
of
> water and in the other it is 10 calcite and 13.9 mole per 100 kilogram of
> water. But if calcite doesn't dissolve and dolomite is in excess, this may
> not make a difference in the results.
>
> I think you need to put 10 moles of calcite in the phast run. You need to
> fix both files if you want the infilling solution to be in equilibrium
with
> calcite. And you probably should fix the ratios of solution to mineral to
> be consistent (phast requires 1 kilogram of water, so you need to change
> phreeqc). These changes would make phast and phreeqc consistent. You need
> then to be sure that the selected values are consistent with the MIN3P
> definitions, but you should be able to get phast to match MIN3P as well.
>
> 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
>
>