Interpretative modelling methods and tools

The widely-used PHREEQC program from the US Geological Survey is based on an ionassociation aqueous model and on equilibrium chemistry of aqueous solutions interacting with minerals, gases, solid solutions, exchangers, and sorption surfaces. It performs a wide variety of low-temperature aqueous geochemical calculations. Its main capabilities of relevance for present applications are (i) mixing of waters with speciation and saturation-index calculations, (ii) batch-reaction and mass transfer calculations of reversible and irreversible reactions involving aqueous, solid and gas phases, and (iii) one-dimensional advective mass transport. PHREEQCI v2.8 (Parkhurst and Appelo, 1999) was used with the PHREEQC rev2.3 thermodynamic database. This expansion of the code includes capabilities to simulate dispersion and diffusion in 1D-transport calculations including matrix exchange in a dual porosity medium, to model kinetic reactions, and to model the formation or dissolution of binary solid solutions, plus some improved flexibility in the input and output of data.