Which of the following methods is commonly used for land disposal of hazardous waste?

The method commonly used for land disposal of hazardous waste is deep well injection. This technique involves the placement of hazardous waste deep underground into geological formations. The injected waste is typically situated below the lowermost underground source of drinking water and is confined in a space that is isolated from freshwater aquifers. This method effectively isolates the waste from the environment and helps prevent contamination of groundwater resources.

Deep well injection is favored because it offers a means of disposing of large volumes of hazardous substances while minimizing the risk of exposure to humans and ecosystems. Additionally, this method is tightly regulated by environmental authorities to ensure that the integrity of the well and surrounding geological formations is maintained, thereby preventing leaks and potential hazardous waste migration.

In contrast, ion exchange is primarily used for water treatment rather than land disposal; neutralization is a chemical process used to render hazardous waste less harmful but does not involve disposal; and electrostatic precipitation is used for air pollution control, particularly in removing particles from industrial exhausts. Thus, the specific focus on land disposal channels the correct choice toward deep well injection as the most suitable method for that purpose.