The behavior of chemical species as they migrate through heterogeneous poro
us media is considered. The so-called "anomalous'' transport patterns frequ
ently measured in these materials are quantified in the framework of a cont
inuous time random walk (CTRW) formalism. The physical basis for applicatio
n of the CTRW is discussed, and new solutions for the first passage time di
stribution are presented to covet the entire range of transport behaviors.
Application of these solutions to analysis of experimental data is also dis
cussed.