Modeling 3-D coupled variably saturated flow, reactive chemical transport, and heat transfer under complex and mixed reaction systems

A three-dimensional numerical model HYDROGEOCHEM 5.0 has been developed to study coupled variably saturated subsurface flow, reactive chemical transport, and heat transfer under complex (multiple reaction types, including aqueous complexation, adsorption-desorption, ion-exchange, redox, precipitation-dissolution, and acid-base reaction) and mixed (equilibrium and kinetic) reaction systems. The theoretical bases and numerical implementations are summarized and one designed example is presented. The complex example simulates steady flow and transient reactive chemical transport in a 3-D domain. It incorporates complexation, adsorption, ion-exchange, and mineral dissolution in a system of mixed equilibrium and kinetic reactions.