Modeling of 36Cl Transport and Water Flow in Amended Gypsiferous- Calcareous Soil

Dissolution of gypsum has great influence on water flow and solute transport occurring ingypsiferous-calcareous soils. Many models based on convection and diffusion processes havebeen developed to describe transport in soil. Constraints of estimation of transport parameters ingypsiferous-calcareous soils are mainly due to gypsum influence .The objectives of this study,were to i: modeling the transport of solute (36Cl) in gypsiferous-calcareous soil treated with fuelof FO on dissolution of gypsum associated with calcium carbonate content. Radiotracer ofchloride as carrier free of 36Cl was applied to surfaces of saturated soil columns that have 20, 250and 500 g kg-1 gypsum treated with 0, 1, 2, and 4% of fuel oil and leached with water untilcomplete displacement of chloride. During leaching, samples of effluent were collected andmeasured for Cl36 . The application of 1 to 2% FO improved the transport properties due tomodification in soil structure. The applied models gave good fit between measured and predictedbreakthrough curves of 36Cl with significant linear correlation coefficient (r) that ranged between0.972 and 0.999. They gave a calculated dispersion coefficient (D) ranging from 2.1 to 79.2 cm2day-1, and retardation factor (R) ranging from 0.92 to 1.58. It was found that D was also linearlyrelated to pore water velocity (v). Also, the results indicate the possibility of predicting thedistribution of chloride in gypsiferous-calcareous soil for different time periods using correctboundary conditions. Experimental results show that gypsum dissolution in the soil columns ismainly determined by the flow velocity, soil saturation and then partially coating with FO. Therole of lime was not well explained in reducing gypsum dissolution because the co-existence ofgypsum and lime is not clear enough.