Department of Geosciences
North Dakota State University
WEB-PHREEQC:
AQUEOUS GEOCHEMICAL MODELLING

For the purposes of this course, we can begin with considering aqueous geochemical modelling to be the calculation of:

• equilibrium concentrations (or activities) of chemical species in solution, and
• the saturation indices (SI's) of solid phases in equilibrium with a solution.

A slightly broader definition includes the calculation of the effects of mixing of waters, adding phases to the solution, changing the solution's temperature, Eh, or pH, etc.

Approximations of this kind of calculation can be done on a hand calculator or on a spreadsheet. More detailed calculations can be done using computer programs such as PHREEQC, WATEQ4F, MINTEQ, EQ3/6, ChemEQL, GEMS, and the Geochemist's Workbench.