A COMPREHENSIVE SET OF ANALYTICAL SOLUTIONS FOR NONEQUILIBRIUM SOLUTETRANSPORT WITH 1ST-ORDER DECAY AND ZERO-ORDER PRODUCTION

Solute transport in the subsurface is often considered to be a nonequi librium process. Predictive models for nonequilibrium transport may be based either on chemical considerations by assuming the presence of a kinetic sorption process, or on physical considerations by assuming t wo-region (dual-porosity) type formulations which partition the liquid phase into mobile and immobile regions. For certain simplifying condi tions, including steady state flow and linear sorption, the chemical a nd physical nonequilibrium transport models can be cast in the same di mensionless form. This paper presents a comprehensive set of analytica l solutions for one-dimensional nonequilibrium solute transport throug h semi-infinite soil systems. The models involve the one-site, two-sit e, and two-region transport models, and include provisions for first-o rder decay and zero-order production. General solutions are derived fo r the volume-averaged (or resident) solute concentration using Laplace transforms assuming both first- and third-type inlet conditions, and arbitrary initial conditions, input solute concentrations, and solute production profiles. The solutions extend and generalize existing solu tions for equilibrium and nonequilibrium solute transport. The general solutions are evaluated for some commonly used input and initial cond itions, and zero-order production profiles. Expressions for the flux-a veraged concentration are derived from the general and specific soluti ons assuming a third-type inlet condition. Typical examples of calcula ted concentration distributions resulting from several sets of initial and input conditions and zero-order production functions are also pre sented and briefly discussed.