VULNERABILITY OF 3 SPATIALLY-VARIABLE SOIL GROUPS FOR SOLUTE LEACHING

Solute leaching in unsaturated soil is influenced by the variability i n hydraulic functions (water retention and conductivity) that govern t he flow process. Variability in measured soil hydraulic functions of a coarse-, medium- and fine-textured soil group was quantified with the scaling theory of similar media. Solute leaching in these soils was c alculated with Monte Carlo simulation assuming, successively, hydrauli c conductivity, K, volumetric water content, theta, and pressure head, h, to be constant. In addition to variability in hydraulic functions, variability in the solute retardation factor was also taken into acco unt. To examine this effect five solutes were considered: a conservati ve solute (chloride), a non-retarded solute subject to decay (nitrate) , a retarded solute that does not decay (cadmium) and two organic solu tes which are retarded but have different sorption and decay parameter s (the pesticide atrazine and a chlorinated hydrocarbon). The numerica l results obtained with Monte Carlo simulation were in a number of ins tances verified with analytical solutions. The three soil groups disti nguished showed considerable differences in vulnerability for leaching of the five solutes, emphasizing the importance of the effect of vari ability in soil hydraulic functions when studying solute leaching. Num erical and analytical results showed good agreement. Therefore, in rel atively simple situations analytical solutions are attractive. However , in complicated situations, analytical solutions are cumbersome and n umerical solutions are the only realistic alternative.