have tried some inverse modeling with PHREEQCI. As you can see from the attached output there are errors flagged relating to a subroutine, although the program gives models. Also, the second attempt yields no models although I can construct one as shown in the exel spreadsheet. My questions are: 1. do i need to worry about the Subroutine Cl1 errors. 2. why don't i get a model for the second attempt (INVERSE_MODELING 5)? The Cl1 errors are coming from the small concentrations of ferrous and ferric iron. Setting the iron concentrations to 0.0 will clear up most of the problems. The second modeling fails because there is no way to account for the small changes in ferrous iron between initial and final solution. A few errors are related to models that generate significant water from mineral reactions. These normally require moles of mass transfer of phases and are not reasonable models. You can set a switch (-mineral_water false) in INVERSE_MODELING to ignore the water generated by mineral reactions and that gets rid of the remaining errors. I don't like to use this switch universally, but this might be a good spot to get rid of some unreasonable models and the error messages as well. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225
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