The two-region model was developed originally to describe nonsorbing c
hemical transport in soils with dead-end pores based on the concept of
mobile and immobile regions in the soil. It has been shown that the m
odel can simulate solute transport in soils with local stratification,
or inhomogeneity, of hydraulic conductivity. However, the physical ba
sis of the model becomes questionable, since the mobile-immobile regio
n concept does not apply in stratified soils. In both soil types the n
onequilibrium effect is caused by an apparent mass transfer process wi
thin the soil, as distinct from advection and diffusion. Where there a
re immobile regions, the mass transfer is due to solute interregion di
ffusion alone. In stratified soils the nonequilibrium mass transfer pr
ocess is affected also by local flow variations. A conceptual model, n
umerical simulations, and laboratory experiments are presented to anal
yze these effects. For a given soil with fixed local stratification of
hydraulic conductivity, it is shown that in the low-velocity range, t
he apparent mass transfer rate parameter, alpha, scales as V2/D (V is
pore water velocity in the two-region model and D is the longitudinal
dispersion coefficient), which implies that the mass transfer process
is predominantly affected by local flow variations. When the velocity
is relatively high, alpha is-proportional-to D(T)/h2 (D(T) is the inte
rregion diffusion coefficient and h is the characteristic thickness of
the stratified layers) and the mass transfer process is dominated by
interregion diffusion. These scaling relations for alpha reflect the t
wo mechanisms controlling the mass transfer process in locally stratif
ied soils. They have implications for scaling of time-dependent mass t
ransfer from laboratory models to prototype soils. In particular, the
relationship alpha is-proportional-to V2/D leads to the conclusion tha
t exact physical modeling of nonsorbing chemical transport coupled wit
h apparent mass transfer in locally stratified soils may be viable.