> In attempting to conduct an inverse model I am receiving an error message that states the model cannot work for the uncertainty of the second solution. > Is there a simple solution for this problem? Any further advice you could give will be very appreciated. There are two reasons you may have gotten this error. (1) You may have a large charge imbalance in the second solution. (check the Initial Solution output for solution 2). PHREEQC allows uncertainty in the analytical data and attempts to adjust concentrations so that charge balance is achieved with the adjusted concentrations. If the charge imbalance is large, then a large uncertainty will be needed to achieve charge balance. In general, the uncertainty must be at least half of the percent error in charge balance to avoid the error you got. (2) PHREEQC automatically includes mole-balance equations for the elements in the phases that you select for inverse modeling. However, elements not included in the phases are ignored unless a mole balance equation is specifically included by the "-balances" option. So if you did not include a phase that contains one of the major constituents in the water analyses, PHREEQC will ignore that element and try to adjust the other elements, for which mole-balance equations are included, to achieve charge balance. If chloride is a major ion and you do not include a phase with chloride, you would very likely get this error. 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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