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Title: NUMERICAL MODEL FOR SIMULATING MULTIPLE SOLUTE TRANSPORT IN VARIABLY- SATURATED SOILS

Author
item SIMUNEK, JIRKA - U.C. RIVERSIDE
item Van Genuchten, Martinus

Submitted to: Ground Water Modeling Conference Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Once released into the subsurface environment, industrial and agricultural chemicals are generally subjected to a large number of simultaneous physical, chemical, and biological processes, including sorption-desorption volatilization, photolysis, and biodegradation, as well as their kinetics. The extent of degradation, sorption and volatilization largely determines the persistence of a pollutant in the subsurface. Mathematical model was developed to simulate the behavior and movement of different chemicals subject to these reactions in soils. The model can calculate the transport of one independent solute, as well as a system of solutes which are coupled by a first order decay. Typical example of such systems are the simultaneous movement of interacting nitrogen species, radionuclides, organic phosphates, and pesticides and their metabolites.

Technical Abstract: In this paper we discuss a two-dimensional model, CHAIN 2D, for simulating the variably-saturated movement of water, heat, and multiple solutes involved in sequential first-order decay reactions. The model assumes that the solutes can reside in all three phases, i.e., liquid, solid, and gaseous. The solute transport equations consider convective-dispersive transport in the liquid phase, diffusion in the gaseous phase, nonlinear equilibrium or nonequilibrium sorption, linear equilibrium volatilization, zero-order production, and first-order degradation reactions which provide the necessary coupling between solutes involved in the sequential first- order decay reactions. Nonlinear sorption is described by a generalized formulation which can be simplified to either a Freundlich or Langmuir equation. Nonequilibrium sorption may be described using both one-site or two-site kinetic reactions. The model considers temperature dependence of all transport and reaction parameters. Typical examples of first-order decay scenarios are the simultaneous movement of interacting nitrogen species, radionuclides, organic phosphates, and pesticides and their metabolites.