This study, considering evidences of slower sorption rates of reactive solutes in the field than in laboratory, quantifies the velocity and retardation factor of a sodium fluorescein (uranin: C₂₀H₁₀Na₂O₅) plume over its travel path in a heterogeneous aquifer. The transport process of uranin was evaluated by batch experiments and from breakthrough curves (BTCs) by using solute-transport models. Method of time moments analysed BTCs of uranin and bromide to derive the velocity and retardation factor.

A constant velocity of the bromide plume, 0.64 m/day, implies a spatially and temporally uniform velocity field where groundwater flows at steady-state condition. A large dimensionless index (195) of chemical non-equilibrium model and equilibrium distribution coefficient (0.32) of uranin are indicative of chemical non-equilibrium transport process.

The travel time of uranin plume increases asymptotically, following power law, with travel path of the plume. Good agreement of the exponent of power law with that of Freundlich isotherm is a result of nonlinear sorption, and provides an independent way of estimating the exponent of the isotherm. The local velocity of the plume decreases asymptotically in time and is predicted by the derivative of the relationship between travel path and travel time of the plume. The retardation factor, which increases in time following power law, when estimated from the local velocity, is considerably larger than that estimated from travel time of the plume.