The PESTAN (Pesticide Analytical) model is a computer code for estimating the transport of organic solutes through soil to groundwater. The model is based on a closed-form analytical solution of the advective-dispersive-reactive transport equation. The model was developed by Enfield, et al. in 1982 and has since been used by the EPA Office of Pesticides Program (OPP) for initial screening assessments to evaluate the potential for groundwater contamination of currently registered pesticides and those submitted for registration (Donigian and Rao 1986). The model has also been tested under field and laboratory conditions (Enfield et al., 1982; Jones and Back, 1984; Melancon et al., 1986). Although the model is based on a simple analytical solution, it may be useful in making preliminary assessments as long as the user is fully aware of its assumptions and limitations. Therefore, it is the principal objective of this User's Guide to provide essential information on the aspects such as model conceptualization, model theory, assumptions and limitations, determination of input parameters, analysis of results and sensitivity analysis (parameter studies). With the information presented, it is hoped that this manual will help the user in making the best possible use of the model.You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.