With a single phase in two dimensions, Yeh and Tripathi [1991] presented a hydrogeochemical multisolute transport model based on the formulation that they had advocated earlier [ Yeh and Tripathi, 1989]. Linear differential transport equations were solved sequentially, iterating between this module and one solving nonlinear algebraic equilibrium equations. Iterative coupling was found to be important, as results differed if only one iteration was taken. Kalatzis et al. [1993] used streamline directional splitting for transport in a two-dimensional LEA model that included sorption as well as reactions in solution. Simunek and Suarez [1994] included transport of carbon dioxide in both the water and gas phases in the unsaturated zone, as well as solute transport in water. The model incorporated detailed chemistry, nonequilibrium kinetics, heat transport, and evapotranspiration. The conservative form [ Celia et al., 1990] of the flow-equation storage term was used, with fixed-point iteration between the transport and chemistry modules.