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SCREENING MODEL FOR VOLATILE POLLUTANTS IN DUEL POROSITY SOILT
Citation:
Hantush*, M M., R. S. Govindaraju, AND M. A. Marino. SCREENING MODEL FOR VOLATILE POLLUTANTS IN DUEL POROSITY SOILT. JOURNAL OF HYDROLOGY 260:58-74, (2000).
Description:
This paper develops mass fraction models for transport and fate of volatile organic chemicals, such as pesticides, in two-region soils. It addressed two main and interrelated parts. First, expressions are derived which describe the rate mass transfer coefficient in a periodical two-region hollow cylindrical and discrete-block porous media, and the scale-dependency of the concept of effective rate transfer coefficient is addressed. It is shown, using conservation of mass, that a discrete-block system may be represented under certain conditions by an equivalent, but a continuous, periodical two region model with a scale-dependent effective rate transfer coefficient. Secondly, mass fraction models are developed, which describe leaching, volatilization losses across the soil-air interface, absorption and degradation in the dynamic- and stagnant- soil regions. It is shown that leaching is the result of the combined effect of the upward vapor-phase transport relative to downward advection, residence time w relative to half-life, dispersion, and lateral diffusive transfer. Because of the complex interaction among the different physical and biochemical processes, the results show that leaching does not always decrease monotonically with increased residence time relative to pesticide's half-life. It is shown that lateral dispersion by diffusive mass transfer into immobile-water region affect considerably leaching and, to a lesser extent, volatilization losses from soil surface. Leaching and losses by volatilization are more significantly impacted by longitudinal dispersion in the dynamic-soil regions. The analysis may be useful to the management of pesticides and the design of landfills.