Deep well injection is a waste disposal technology that has been used for decades in the United States, but concerns about its increased use are raising questions about its efficacy. The primary concerns are linked to the potential for groundwater and aquifer contamination as well as geological damage, mainly whether the practice of boring deeply into the earth might trigger small earthquakes.
The United States Environmental Protection Agency’s (EPA) Federal Remediation Technologies Roundtable describes deep well injection as “a liquid waste disposal technology.” It says:
This alternative uses injection wells to place treated or untreated liquid waste into geologic formations that have no potential to allow migration of contaminants into potential potable water aquifers. […] Injection wells have been used for the disposal of industrial and hazardous wastes since the 1950s, so the equipment and methodology are readily available and well known; however the use of them today is continuing under very strict regulatory control.
Deep well injection use rapidly increased in the 1960s and 1970s, and was initially regulated by the Federal Water Quality Administration prior to the creation of the United States Environmental Protection Agency. A statement of federal policy was issued acknowledging that it was a finite solution for waste disposal requiring regulation.
According to the EPA:
A typical injection well consists of concentric pipes, which extend several thousand feet down from the surface level into highly saline, permeable injection zones that are confined vertically by impermeable strata. The outermost pipe or surface casing, extends below the base of any underground sources of drinking water (USDW) and is cemented back to the surface to prevent contamination of the USDW.
The practice has been used to treat wastewater as well as dispose of hazardous chemicals.
“Deep well injection of treated municipal wastewater into non-potable aquifers has been used as an alternative to discharge of wastewater to surface waters for many decades,” according to Virginia Walsh and René Price writing in a 2010 Hydrogeology Journal paper. In 2008, the EPA listed 430 permitted municipal wastewater deep injection wells in the United States, 163 of which were sited in Florida.
The authors note:
These deep aquifers tend to be saline, and the discharge of fresh wastewater into them has raised concerns of geochemical reactions as a result of the mixing of the two waters, as well as the buoyant transport of the wastewater upwards into overlying aquifers. Confined brackish aquifers in Florida have been used extensively for aquifer storage and recovery (ASR) of potable freshwater […] and deeper saline aquifers have been used for disposal of waste fluids such as oil brines, industrial water and municipal wastewater.
The treatment practice has been deemed safe, according to the Rocky Mountain Arsenal Remediation Venture Office, which has its own 12,045-foot-deep well, constructed in 1961 to dispose of 165 million gallons of liquid waste between 1962 and 1966. The Army states the briny waste included “some metals, chlorides, wastewater and toxic organics.” Its use was discontinued in February 1966 because “of the possibility that the fluid injection was triggering earthquakes in the area.” The well was sealed in 1985.
The National Resources Defense Counsel notes that deep well injection is frequently used in shale gas exploration as a method to dispose of fracking wastewater; however, there is concern about groundwater contamination associated with the disposal practice as well as the potential for earthquakes. Some water from drilling in Pennsylvania, for example, is being transported to Ohio for disposal.
According to a paper in the 1996 Pace Environmental Law Review:
For industry, deep-well injection is a precious, limited resource. There are only so many places in which hazardous wastes can be disposed of with confidence. Many people in industry believe properly managed deep-well injection can be a useful tool, offering benefits that far outweigh its inherent risks. With the ever-increasing mass of waste produced as a result of society’s demand for consumer goods, deep-well injection is a mainstay method of hazardous waste disposal for which no true replacement technology currently exists.