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Tracing Water Flow and Colloidal Particles Transfer in an Unsaturated Soil

Journal of Water Resource and Protection 2014年第7期6卷 696-709页

作者： Dieuseul Prédélus Laurent Lassabatere Artur Paiva Coutinho Cédric Louis Thomas Brichart erij ben slimène Thierry Winiarski Rafael Angulo-Jaramillo Nano-H S.A.S. 38070 Saint Quentin Fallavier France Universidade Federal de Pernambuco Recife Brazil Université de Lyon CNRS UMR 5023 LEHNA ENTPE Vaulx-en-Velin France Universidade Federal de Pernambuco Recife Brazil

In recent years, many studies have been carried out on colloidal particle transfer in the unsaturated zone because they can be a risk to the environment either directly or as a vector of pollutants. A study was conducted on the influence of porous media structure in unsaturated conditions on colloidal particle transport. Three granular materials were set up in columns to replicate a fluvio-glacial soil from the unsaturated zone in the Lyon area (France). It is a sand, a bimodal mixture in equal proportion by weight of sand and gravel, and a fraction of bimodal mixture. Nanoparticles of silica (SiO2-Au-FluoNPs), having a hydrodynamic diameter between 50 and 60 nm, labeled by organic fluorescent molecules were used to simulate the transport of colloidal particles. A nonreactive tracer, bromide ion (Br-) at a concentration of C0,s = 10-2 M was used to determine the hydrodispersive properties of porous media. The tests were carried out first, with a solution of nanoparticles (C0,p = 0.2 g/L) and secondly, with a solution of nanoparticles and bromine. The transfer model based on fractionation of water into two phases, mobile and immobile, MIM, correctly fits the elution curves. The retention of colloidal particles is greater in the two media of bimodal particle size than that in the sand, which clearly demonstrates the role of textural heterogeneity in the retention mechanism. The increase in ionic strength produced by alimenting the columns with colloidal particle suspension in the presence of bromide, increases retention up to 25% in the sand. The total concentration profile of nanoparticles collected at the end of the experiment shows that the colloidal particles are retained primarily at the entrance of the columns. Hydrodispersive calculated parameters indicate that flow is more heterogeneous in bimodal media compared to sand.

关键词： Colloidal Particle Transport Microstructure Modeling Unsaturated Soil

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Modeling Water Infiltration and Solute Transfer in a Heterogeneous Vadose Zone as a Function of Entering Flow Rates

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Journal of Water Resource and Protection 2015年第13期7卷 1017-1028页

作者： erij ben slimene Laurent Lassabatere Thierry Winiarski Remy Gourdon Laboratoire d’Ecologie des Hydrosystèmes Naturels et Anthropisés (LEHNA) ENTPE Vaulx-en-Velin France Laboratoire de Génie Civil et d’Ingénierie Environnementale-Déchets Eau Environnement et Pollutions (LGCIE-DEEP) INSA Lyon Villeurbanne France

Due to its rapid movement, preferential flow (PF) in the vadose zone allows much faster contaminant transport, which may have a significant impact on ground-water quality. PF can occur in heterogeneous vadose zones and it strongly depends on hydric and hydraulic conditions like entering flow rates at surface. This study deals with the modeling of the establishment of PF, and related solute transfer during the infiltration phase in a strongly heterogeneous glaciofluvial deposit. This deposit is made of four contrasting lithofacies (sand, gravel, bimodal gravel and matrix-free gravel) and lies underneath an urban infiltration basin (Lyon, France). Previous studies have been carried out on this site and linked the regionalization of soil pollution with the lithological heterogeneity. But none of them clearly demonstrated how heterogeneity could impact flow and solute transfer and may explain such a regionalization. In this study, we model flow and solute transfer at the trench scale for both uniform and heterogeneous profiles in order to characterize the effect of lithological heterogeneity. In addition, such a modeling was performed for two different entering flow rates to depict the influence of condition at surface on PF. A key result is that heterogeneity clearly impacts unsaturated flow and solute transfer. Numerical modeling permitted pointing out the existence of PF paths associated with the sedimentary heterogeneity of the glaciofluvial deposit. For lower surface fluxes, the sand lens and matrix-free gravel were the sources of capillary barrier effects, leading to a funneled flow and a groundwater recharge characterized by earlier and more dispersed wetting fronts. Such a flow pattern enhances solutes transfer and reduces solute retention by soil. Thus, the effect of heterogeneity on solute transfer is significant, especially for the most reactive solutes.

关键词： Numerical Modeling Preferential Flow Solute Transfer Infiltration Basin Vadose Zone

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