> Estimation of rates of formation of phases is not possible with Phreeqc. I'm not sure what you want here. PHREEQC has a kinetics module that allows kinetic reactions to be modeled either in batch or a 1D transport environment. There is no direct estimation of reaction rates, but rates of reactions can be modeled by parameter estimation in a 1D column, provided flow velocities are known. The program PHAST is on the web (http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phast) which allows for 3D modeling of flow, transport, and reactions and has all of the chemical capabilities of PHREEQC. > And formation of silicates in brines (the saline groundwaters are very old and silicate concentrations are high: up to 50 mg/L Si) is not handled by Phrqpitz. Would you know whether Solmineq and GAMSpath do things that Phreeqc does not. To my knowledge, the Pitzer parameterization for aqueous silica (or aluminum) species does not exist. Thus, I do not think any of the models that use the Pitzer specific-interaction approach have the capability to model silicate reactions. I'm not familiar with GAMSpath, but I suspect it is Solmineq with some kinetics added on top. The advantage of this program may be that you can model kinetic reactions with the Pitzer approach, whereas PHREEQC is limited to the ion-association approach. They also claim to have kinetic expressions for all minerals in their database, but I am dubious that this information would be adequate for a field investigation. The advantages of PHREEQC are more types of reactions that can be modeled, more general kinetics, and advection-dispersion-reaction modeling (3D with PHAST). David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 "RG&AJ Gerritse" <geoprocc@xxxxxx To: "david parkhurst" <dlpark@xxxxxxxx> net.au> cc: "Tony Appelo" <appt@xxxxxxxxx> In-Reply-To: <000c01c0b8df$626cf720$b165a8ca@xxxxxxxxxxx> Subject: comparing Preeqc 03/29/01 06:33 PM Dear David and Tony, I hope you don't mind me asking you a question on how Prheeqc compares with Solmineq and GAMSpath. I regularly use Phreeqc (and Phrqpitz) for modelling alkaline contaminated and calcitic groundwaters under mine sites and highly saline groundwaters in the SW of Western Austr. (used in gold mining). Estimation of rates of formation of phases is not possible with Phreeqc. And formation of silicates in brines (the saline groundwaters are very old and silicate concentrations are high: up to 50 mg/L Si) is not handled by Phrqpitz. Would you know whether Solmineq and GAMSpath do things that Phreeqc does not. Thanks regards dr Robert Gerritse Geoprocc Pty Ltd 64 Hamer Ave Wembley Downs Australia WA 6019
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