Models Link Fundamental Research with Practice: PRB Examples

 An important role of models in the ground water field is in their service as facilitators for information exchange between rigorous theoretical science and the job of quantitatively applying hydrogeology to solve real-world problems and make predictions.  The widespread use of codes such as MODFLOW and PHREEQC by practitioners not fluent in the computer codes, or even all the details of the underlying theory, exemplifies the importance of that role.  In addition, models are commonly used to investigate parameter sensitivities, providing information about the range of outcomes that might follow some sort of perturbation.  However, models can also operate in a more subtle role, providing a framework for extracting down-to-earth, practical insights from seemingly esoteric datasets.  For example, the study of reaction rates between various organic contaminants, including nitroaromatics and chlorinated solvents, and granular iron led to the development of a hitherto unreported chemical kinetic model.  The use of this model to interpret batch and column tests led to an understanding of the limits to which iron permeable reactive barriers (PRBs) can be diluted with sand without fear of performance losses.  In addition, the model distinguishes between sorption controlled rate and electron transfer controlled rate thereby providing insights on the factors controlling the iron lifetime.  In these examples, the mathematical model was an essential link between the experimental data, a conceptual model, and insights of practical value for the construction and maintenance of PRBs.  This use of models deserves increased recognition along with the better known uses mentioned above.