natural setting. Although concurrence of model-simulated and
independently derived parameters does not prove the correctness of the
model's underlying theoretical basis per se, overall confidence in the
model's theoretical basis is increased as concurrence continues to
exist under a variety of characterized conditions. Increased
confidence allows greater use of the model for purely predictive and
managerial purposes.
Numerous models have been proposed for describing solute
transport in aggregated porous media. Modeling solute transport in
aggregated or structured soils presents some unique problems due to the
complex three-dimensional nature of the inter-connected network of
irregularly sized and shaped soil pores. Attempts to model
displacement processes quantitatively have been based generally on the
convective-dispersive equation (Lapidus and Amundson, 1952),
ac/at = D a2C/az vo ac/az [4-1]
where C is the concentration (mg/mL), D is the dispersion coefficient
(cm2/day), vo is the pore-water velocity (cm/day), z is the distance
(cm), and t is time (days).
Adsorption of the solute to the porous
media may be considered using an adsorption coefficient derived from a
linear adsorption isotherm, defined by
S = KC [4-2]
where S is the sorbed solute concentration (mg/g), C is the equilibrium
solution solute concentration (mg/mL), and Kd is the adsorption
coefficient (mL/g) giving
R ac/at = D a2/az2 vo ac/az [4-3]