There are two main types of ground-water pollution caused by man: (1) pollution caused by the use of pesticides, herbicides, and fertilizers over agricultural lands, where the source of contamination covers a relatively large area, and (2) pollution caused by industries and municipalities, which is generally more localized. In localized situations, the design of any remedial measure requires knowledge of the extent of the contaminant plume. Various mathematical methods may be used for estimating the size, shape, and development of a localized contaminant plume. The present handbook introduces the reader to various mathematical methods for estimating solute transport in ground-water systems. It contains tables, figures, and simple computer programs that can be directly used for field studies. Three levels of mathematical methods are covered: (1) analytical, (2) semianalytical, and (3) numerical. The first two levels require relatively small amounts of data. At the third level, numerical approaches are discussed and a number of currently available numerical models are listed, indicating code capabilities and code developers to be contacted for further information. An example of the use of one such model is presented in Appendix J. A discussion on method selection and data requirements is also included.