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 > >
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