A simplified approach to evaluation of column experiments as a tool for determination of radionuclide transport parameters in rock-groundwater or soil-groundwater systems

The assessment of the ability of natural barriers to retain radionuclides and retard their transfer in groundwater requires knowledge of important transport parameters, the retardation and dispersion coefficients. The use of dynamic techniques is in this task more effective than that of batch technique, as the conditions of dynamic experiments better simulate the real systems, in which the contaminated groundwater is flowing through the bed of a porous (grained) solid material (crushed rock, soil, or sediment). Two techniques of the contaminant inlet, the pulse injection and step (continuous) inlet are obviously applied. Dynamic column experiments make possible to study the influence of sorption or desorption of studied contaminants on the velocity of their transport through the saturated or unsaturated bed. The transport parameters are determined in the course of evaluation of experimental data, which generally consists of the regression of breakthrough curve by selected analytical solution of the 1-D advection-dispersion equation. With the respect to the kinetics of the contaminant interaction with the surface of the solid phase, there are two basic groups of these solutions: the first responds to the equilibrium dynamics, and the second one to so-called non-equilibrium dynamics. In description of interaction, that implies the mathematical form of the solution of transport equation, it is further possible to specify both the equilibrium isotherm (linear or non-linear) and the type of kinetic equation (e.g., linear driving force model). In this paper, a set of simplified equilibrium dynamic models is presented, that could be recommended for the evaluation of an important range of column experiment in heterogeneous systems accomplished under the equilibrium dynamics conditions.