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 > >
Please note that some U.S. Geological Survey (USGS) information accessed through this page may be preliminary in nature and presented prior to final review and approval by the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the sole responsibility of the user.
Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.
The URL of this page is:
Last modified: $Date: 2005-09-13 21:04:21 -0600 (Tue, 13 Sep 2005) $
Visitor number 2096 since Jan 22, 1998.