The section will deal with four hazardous waste disposal options, i.e., landfills, geologic formations, chemical stabilization, and chemical treatment. Landfilling has been the traditional method of disposing of hazardous waste. Improper land disposal has led to numerous cases of ground- and surface-water pollution. As a result of environmental damages created by poorly designed landfills, Congress placed stringent criteria on landfills when it passed 'The Hazardous and Solid Waste Amendments of 1984.' For this chapter, geologic formation disposal will include the placement of hazardous waste in injection wells, salt formations, and underground mines. Chemical stabilization/solidification will include processes that reduce the hazard potential of a waste by converting the contaminants into their least soluble, mobile, or toxic form. Chemical treatment comprises a set of technology tools used to prevent the release of hazardous materials into the environment.