Injection of liquid wastes into subsurface geologic formations is a technology that has been widely adopted as a waste-disposal practice. The practice entails drilling a well to a permeable, saline-bearing geologic formation that is confined above and below with impermeable layers known as confining beds. When the injection zones lie below drinking water sources at depths typically between 2,000–5,000 ft (610–1,525 m), they are referred to as Class I disposal wells. The liquid hazardous waste is injected at a pressure that is sufficient to replace the native fluid and yet not so high that the integrity of the well and confining beds is at risk. Injection pressure is a limiting factor because excessive pressure can cause hydraulic fracturing of the injection zone and confining strata, and the intake rate of most injection wells is less than 400 gal (1,500 l) per minute.

Deep-well injection of liquid waste is one of...