Descriptive models which attempt to fit mathematical equations to existing experimental data. For many contaminants predictive models are able to accurately calculate breakthrough times. A predictive model has been developed by G. O. Wood. This model utilizes chemical and physical properties to estimate the breakthrough time.
Descriptive models use experimental data to calculate parameters which fit the model to the data.
Once the model is fit to a set of experimental data, the model is used to calculate values for points where experimental data are not available. The validity of the model is dependant on the accuracy of the experimental data. An equation developed by Yoon-Nelson is presented as an example.