Contaminant Transport In Unsaturated Zone Research Articles

AN ANALYSIS OF THE EFFECT OF HYDRAULIC PARAMETERS ON RADIONUCLIDE MIGRATION IN AN UNSATURATED ZONE

A One-Dimensional Water Flow and Contaminant Transport in Unsaturated Zone (FTUNS) code has been developed in order to interpret radionuclide migration in an unsaturated zone. The pore-size distribution index (n) and the inverse of the air-entry value (α) for an unsaturated zone were measured by KS M ISO 11275 method. The hydraulic parameters of the unsaturated soil are investigated by using soil from around a nuclear facility in Korea. The effect of hydraulic parameters on radionuclide migration in an unsaturated zone has been analyzed. The higher the value of the n-factor, the more the cobalt concentration was condensed. The larger the value of α-factor, the faster the migration of cobalt was and the more aggregative the cobalt concentration was. Also, it was found that an effect on contaminant migration due to the pore-size distribution index (n) and the inverse of the air-entry value (α) was minute. Meanwhile, migrations of cobalt and cesium are in inverse proportion to the Freundich isotherm coefficient. That is to say, the migration velocity of cobalt was about 8.35 times that of cesium. It was conclusively demonstrated that the Freundich isotherm coefficient was the most important factor for contaminant migration.

Effect of immobile water content on contaminant transport in unsaturated zone

The effect of immobile water content on contaminant advection and dispersion in unsaturated porous media has been studied using a formulation which assumes that even in the immobile liquid zone, there occurs minor liquid flow. An approach is proposed for computing this liquid velocity. One dimensional numerical simulation is carried out to study the effect of immobile water content on the time of appearance of contaminant at the bottom of an unsaturated column. The numerical model developed is verified using analytical solutions for simple advective-dispersive cases. From the simulations, it was observed that increase in the immobile water content leads to quicker appearance of contaminant.

SIMULATING WATER MOVEMENT AND ITS UPTAKE BY PLANT ROOTS IN UNSATURATED ZONES

Existing mathematical models that simulate water movement and contaminant transport in unsaturated zone do not take into account the water uptake by plant crop roots resulting in an error in the prediction of water flux and, thereby, contaminant concentration. Moreover the application of these models is often limited due to the lack of easily accessible and representative soil hydraulic properties, like moisture retention characteristic and unsaturated hydraulic conductivity. In this study, a mathematical model is developed for simulating water movement in unsaturated zones by integrating the one‐dimensional transient unsaturated water flow equation (Richard's equation) with a root water extraction term (sink), and also incorporates pedo‐transfer functions (PTF) for estimating soil hydraulic properties. The governing non‐linear partial differential equation is solved numerically by the implicit finite difference method using Picard's iterative technique, the formulation has been illustrated by a characteristic example.

Fluid-solid coupling mathematical model of contaminant transport in unsaturated zone and its asymptotical solution

The process of contaminant transport is a problem of multicomponent and multiphase flow in unsaturated zone. Under the presupposition that gas existence affects water transport, a coupled mathematical model of contaminant transport in unsaturated zone has been established based on fluid-solid interaction mechanics theory. The asymptotical solutions to the nonlinear coupling mathematical model were accomplished by the perturbation and integral transformation method. The distribution law of pore pressure, pore water velocity and contaminant concentration in unsaturated zone has been presented under the conditions of with coupling and without coupling gas phase. An example problem was used to provide a quantitative verification and validation of the model. The asymptotical solution was compared with Faust model solution. The comparison results show reasonable agreement between asymptotical solution and Faust solution, and the gas effect and media deformation has a large impact on the contaminant transport. The theoretical basis is provided for forecasting contaminant transport and the determination of the relationship among pressure-saturation-permeability in laboratory.