DETERMINING LOCAL-SCALE SOLUTE TRANSPORT PARAMETERS USING TIME-DOMAIN REFLECTOMETRY (TDR)

The time domain reflectometry (TDR) technique was evaluated as a viable method for quick and accurate characterization of the solute transport parameters in controlled laboratory conditions. The method is able to measure steady-state solute breakthrough curves of inert solutes in soil columns. Transport of a solute was monitored in a column uniformly packed with a disturbed sandy material and columns filled with undisturbed soil material of three different soil horizons of a sandy soil profile. The measured solute breakthrough curves were used to assess the parameters of the classical two-parameter convection dispersion equation (CDE), in which it is assumed that the solute is completely miscible. Alternatively, a four-parameter two-region model was fitted to the data, assuming exchange between immobile and mobile water. The study reveals that transport of solutes in undisturbed sandy soil is much better described using the two-region model. In addition, it has been shown that the apparent dispersion coefficient of the CDE could be linearly related to the solute pore water velocity.