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: http://wwwbrr.cr.usgs.gov/projects/GWC_coupled
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