A key objective of the USGS Toxic Substances Hydrology (Toxics) Program is to understand the physical, chemical, and biological processes that control contaminant transport in ground water. Many Toxics Program scientists participate in multidisciplinary investigations of the reactive and non-reactive transport of contaminants in ground water. A part of many of these investigations is the development of simulation models to predict contaminant transport in ground water. Environmental professionals can use the results of these investigations to design better remediation plans at hazardous waste cleanup sites. The information presented on this page cuts across lines drawn by individual investigations and projects so that information on contaminant transport in ground water can be presented in one place.