The Use of Multicomponent Solute Transport Models in Environmental Analyses

This chapter provides a brief overview of multicomponent solute transport models, which simulate the subsurface transport of multiple ions that may mutually interact, can create various complex species, can compete with each other for sorption sites, and/or can precipitate or dissolve. These models are broadly divided into two major groups, those with specific chemistry and general models, and typical examples of these models are given. More detail is provided for the UnsatChem and HPx modules of HYDRUS. The applicability of the UnsatChem module to simulate the multicomponent transport of major ions is demonstrated using the data from a field experiment involving irrigation with waters of different quality, carried out in Portugal. The second example illustrates the use of HP1 to simulate the fate of mercury in a contaminated soil. Finally, the third example demonstrates the versatility of HP2 to simulate the release and migration of uranium from a simplified uranium mill tailings pile toward a river. Using these three examples, it is demonstrated that in spite of the considerable demand on input data, the multicomponent solute transport models can be effective and versatile tools for evaluating complex agricultural and environmental problems.