Geochemical Transport

Geochemical models can be divided into two major groups: those with specific chemistry and general models. Models with specific chemistry are limited in the number of species they can handle, and their application is quite restricted to problems having a prescribed chemical system. Typical examples of models with specified chemistry are those simulating the transport of major ions such as Leaching Estimation And CHemistry Model, and UNSATCHEM, or reclamation models. The UNSATCHEM model takes into account effects of solution composition on hydraulic properties. Models with generalized chemistry provide users with much more freedom in designing their particular chemical systems; possible applications of these models are also much wider. This chapter provides an overview of the mathematical equations representing the major chemical reactions and governing transport processes, discusses how these equations can be implemented in reaction multispecies transport models, and describes several possible applications relevant to soil scientists.