Étude de la migration du soluté d’un lixiviat dans un sol non saturé par la méthode TDR

Abstract

The protection of the environment requires building waste containment systems made up of liners of compacted soil. In this paper, infiltration tests are carried out on soil columns equipped with TDR probes to investigate how water and pollutants migrate in the liners. The TDR method is a technique to measure simultaneously the volumetric water content and the electrical conductivity lor the impedance) of the soil in a continuous manner. Using six soils and three different leachates, new relationships between the volumetric water content (θ) of the soil and its dielectric constant (e) is established. These relationships appear to be more accurate than the one of Topp et al. (1980). They are used to determine water content profiles in a soil column. The relationship between the leachate solute concentration and the electrical conductivity allows to compute the solute concentration profiles in the soil column and the solute breakthrough curve. These curves are used to determine solute convection rate and solute apparent dispersion coefficient. Infiltration test results show that the soil permeability and the diffusivity increase when the leachate is infiltrated. The infiltration rate and the solute convection rate are higher than the leachate outflow rate and the three rates yield to a same value which depends on the soil permeability. The Green and Ampt (1911) model applied to the infiltration shows that the movement of the wet front is faster than the movement of the pollution front. The apparent dispersion coefficient and the solute convection rate are computed by applying the statistic distribution law to the moisture and the solute concentration profiles. It is observed that the apparent dispersion coefficient increases during the saturation of the sample. The electrical conductivity and the solute concentration of the percolated leachate are scaled with the initial values. The evolution curves of these scaled values with elapsed time are used to compute the apparent dispersion coefficient. There is little difference between the apparent dispersion values obtained with the scaled electrical conductivity evolution curve and the scaled solute concentration evolution curve. The use of the TDR measurements allows comparison between solute and water migration parameters and the obtained results can be applied to in situ permeability measurements.