> I would be most appreciated if you could provide information related to USGS's expertise in modelling the dependence of water pH over temperature, pressure and salinity. We have a number of models designed to investigate the chemistry of natural waters: phreeqc, wateq4f, phrqpitz, and solmineq. PHREEQC is the most versatile of the three, but solmineq has more capabilities related to high pressure and high salinities, and phrqpitz is also a better model for high salinities. PHREEQC is limited to relatively low ionic strengths (< 1 molal), but allows for a wider range of geochemical reactions (silicates and redox). Pressure effects are relatively small unless you are at several km depth. The pH of natural waters depends predominantly on CO2 and carbonate equilibria, but may be controlled by a wide variety of reactions. PHREEQC has capabilities to calculate speciation given a pH and water composition. PHREEQC also has capabilities to predict pH given assumptions about initial water composition, mineral equilibria, mass-transfers of reactants, and, if necessary, kinetic reactions. PHRQPITZ is an older FORTRAN program, which has the Pitzer formulation for activities of ions. Solmineq, EQ3/6, Geochemists Workbench, and TEQUIL also include this thermodynamic model and may be simpler to use if they are available. PHREEQC and phrqpitz can be found at the web site given below. Wateq4f is available from https://wwwbrr.cr.usgs.gov/projects/GWC_chemtherm. You will have to contact Yousif Kharaka (ykharaka@xxxxxxxx) for information about solmineq. 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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