Model Usefulness and Limitations

Accurate model prediction, no matter how practical it is, can be obtained only by understanding the underlying science. In this case, the prediction of mass transport in the subsurface can only be accurate if we understand the geochemical reactions that occur in the aquifer. This requires that we understand the geochemical properties of the aquifer, have the thermodynamic and kinetic properties of the chemical system in hand, and understand the interplay among chemical, physical, and biological processes. 

Currently, there are a number of fundamental processes in geochemistry that are not well understood, and which limit the applications and usefulness of geochemical modeling. 

Most models only simulate the batch type of chemical systems, and lack the time and spatial information needed to address a site-specific problem, e.g., the arrival of a contaminant at a particular point in space. This type of model, however, can be useful in evaluating some laboratory experiments. 

There is a general lack of kinetic data for critical environmental and geochemical processes. Additionally, despite recent advances in chemical kinetics, the applicability of laboratory kinetic data to field situations is still uncertain. There is a large discrepancy between laboratory and field derived rate constants (Lasaga, 

Although the importance of surface adsorption is well recognized, critical issues still remain such as how to characterize the effective surface areas of the sorbents and the applicability of laboratory data to the field. 

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