A general description of the mathematical and numerical formulations used in modern numerical reactive transport codes relevant for subsurface environmental simulations is presented. The formulations are followed by short descriptions of commonly used and available subsurface simulators that consider continuum representations of flow, transport, and reactions in porous media. These formulations are applicable to most of the subsurface environmental benchmark problems included in this special issue. The list of codes described briefly here includes PHREEQC, HPx, PHT3D, OpenGeoSys (OGS), HYTEC, ORCHESTRA, TOUGHREACT, eSTOMP, HYDROGEOCHEM, CrunchFlow, MIN3P, and PFLOTRAN. The descriptions include a C. I. Steefel ( ) · B. Arora · S. Molins · N. Spycher

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[1] In this work, a multicomponent lattice Boltzmann (LB) model is presented for simulating reactive transport in porous media at the pore scale. In the model, a set of distribution functions is introduced to simulate fluid flow and solute transport. The model takes into account advection, diffusion, homogeneous reactions among multiple aqueous species, and heterogeneous reactions between the aqueous solution and minerals, as well as changes in solid and pore geometry. Homogeneous reactions are described through local equilibrium mass action relations. Mineral reactions are treated kinetically through boundary conditions at the mineral surface. The LB equation for flow recovers the correct pore-scale continuity and Navier-Stokes equations. The LB equations for solute transport are modified to recover advection-diffusion equations for total concentrations at the pore scale. The model is applied to a hypothetical three-component system with two aqueous complexes and two mineral reactions in a simple pore geometry. The effects of advection, diffusion, reaction rate constants, equilibrium constants of both homogeneous and heterogeneous reactions, and chemical compositions on mineral alteration of the porous medium and solute concentration are analyzed.

Breakthrough curves for Ca 2+ , Mg 2+ and Na + compared with experimental results from Voegelin et al.