Unsaturated zone modeling approaches

Soil models tend to be based on first-order kinetics thus, they employ only first-order rate constants with no ability to correct these constants for environmental conditions in the simulated environment which differ from the experimental conditions. This limitation is both for reasons of expediency and due to a lack of the data required for alternative approaches. In evaluating and choosing appropriate unsaturated zone models, the type, flexibility, and suitability of methods used to specify needed parameters should be considered. 

Rock. In Scaling Methods in Soil Physics Pachq)sky, Y. A., Radcliffe, D. E., Selim, H. M., Eds. CRC Press Boca Raton, FL, 2003 pp 373-417. Pruess, K. Faybishenko, B. Bodvarsson, G. S. Alternative Concepts and Approaches for Modeling Flow and Transport in Thick Unsaturated Zones of Fractured Rocks. J. Contam. Hvdrol. 1999.38 (1-3), 281-322. 

The approach is very commonly used in transport models because mathematically it is relatively easy to incorporate. Goyette and Lewis [28] highlighted the utihty of values in screening level ground water contaminant transport models of inorganic ions with the caution that experimental conditions such as pH, electrolyte composition and soil type are similar to those being modeled. Viotti et al. [29] used values to model phenol transport in an unsaturated soil. Schroeder and Aziz [30] used this approach to account for PCBs sorption into dredged materials. Buczko et al. [31] used the Freundlich approach to model chromium transport in unsaturated zone. 

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