Chloride migration in heterogeneous soil: 1. Experimental methodology and results

Abstract

The statistics of chloride transport through 29 undisturbed soil monoliths (20 cm in diameter and 1 m long, sampled from a field plot of 15×175 m 2 ) were evaluated in a controlled laboratory experiment. Although the field soil (loamy sand) was relatively homogeneous with regard to texture, the individual monoliths showed large and irregular variability in their soil characteristics and in their flow and transport properties. The distribution of the specific discharge of water could be quantified by a bimodal distribution; the horizontal correlation length for the specific discharge of water was estimated to about 10 m. The ratio between the arrival time of the peak in chloride concentration and the water residence time given by the measured flow parameters indicated a mobile water content that was smaller than the measured water content. The large variability in hydraulic conductivity in both the vertical and horizontal direction, and the agreement between the present hydraulic conductivity measurements and earlier measurements in the field area, indicate that the partition of the measured water content between mobile and relatively immobile water was an effect of the soil structure rather than a boundary effect.