text: Reactive transport models are constructed to understand the composition of natural waters; the origin of economic mineral deposits; the formation and dissolution of rocks and minerals in geologic formations in response to injection of industrial wastes, steam, or carbon dioxide; and the generation of acidic waters and leaching of metals from mine wastes. They are often relied upon to predict the migration of contaminant plumes; the mobility of radionuclides in waste repositories; and the biodegradation of chemicals in landfills. When applied to the study of contaminants in the environments, they are known as fate and transport models.