Estimation of Water Vapor Transport in Unsaturated Soils under Osmotic Potential

The transport process of chemical-fertilizers, radioactive materials and other solutes in soils and porous media is important to understand the environmental and economic effects of industrial, agricultural and urban waste disposal methods. In unsaturated porous media, large gradient in aqueous osmotic potential derives significant water vapor fluxes towards regions of high solute concentrations. In this research, the effects of osmotic potential (resulting from salinities of 0.5, 1 and 1.5%) on water vapor transport in three soil textures (silty clay loam, loam and sandy loam) were examined by using a physical laboratory model. Then, the experimental results were compared with Kelly and Selker (2001) model for validation of the predicted water vapor transport. The results showed that the rate of water vapor transport reduces significantly as soil texture gets heavier. For example, in salinity of 0.5% and 5th day of experiment, the amount of transported vapor in sandy loam, loam and silty clay loam soils was 0.362, 0.196 and 0.12 kg/m2, respectively. Large osmotic potential near the high solute concentration in soils caused significant vapor movement toward dense solutions. In salinity of 1.5%, transported vapor in these soils was 1.47, 0.723 and 0.38 kg/m2, respectively. Total water vapor movement until the 15th day was more than the 5th day. Comparison of experimental results with Kelly and Selker model results, using Mathcad PLUS 6.0 software, showed a good agreement between the observed and predicted data. Since water vapor delivered from uncontaminated soils to the contaminated soils can result in increased contaminant plume volume, these physical and chemical processes must be included in the predictive models of contaminant transport in the vicinity of concentrated sources