Typical Deep Well Injection System
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. Directly inside the surface casing is a long string
casing that extends to and sometimes into the injection zone. This casing is filled in
with cement all the way back to the surface in order to seal off the injected waste from
the formations above the injection zone back to the surface. The casing provides a seal
between the wastes in the injection zone and the upper formations. The waste is injected
through the injection tubing inside the long string casing either through perforations in
the long string or in the open hole below the bottom of the long string. The space between
the string casing and the injection tube, called the annulus, is filled with an inert,
pressurized fluid, and is sealed at the bottom by a removable packer preventing injected
wastewater from backing up into the annulus.
Underground injection, Class I injection wells.
The target contaminant groups
for deep well injection are VOCs, SVOCs, fuels, explosives, and pesticides. However,
existing permitted deep well injection facilities are limited to a narrow range of
specific wastes. Success at expanding existing permits to manage hazardous wastes seems
Factors that may limit the applicability and
effectiveness of these processes include:
- Injection will not be used for hazardous waste disposal in any areas where seismic
activity could potentially occur.
- Injected wastes must be compatible with the mechanical components of the injection well
system and the natural formation water. The waste generator may be required to perform
physical, chemical, biological, or thermal treatment for removal of various contaminants
or constituents from the waste to modify the physical and chemical character of the waste
to assure compatibility.
- High concentrations of suspended solids (typically >2 ppm) can lead to plugging of
the injection interval.
- Corrosive media may react with the injection well components, with injection zone
formation, or with confining strata with very undesirable results. Wastes should be
- High iron concentrations may result in fouling when conditions alter the valence state
and convert soluble to insoluble species.
- Organic carbon may serve as an energy source for indigenous or injected bacteria
resulting in rapid population growth and subsequent fouling.
- Waste streams containing organic contaminants above their solubility limits may require
pretreatment before injection into a well.
- Site assessment and aquifer characterization are required to determine suitability of
site for wastewater injection.
- Extensive assessments must be completed prior to receiving approval from regulatory
A detailed discussion of data
elements is provided in Subsection 2.2.2 (Data
Requirements for Ground Water, Surface Water, and Leachate).
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.
Technologies: Field Scale Demonstration Project in North America,
of Remediation Case Studies, Volume 4, June 2000, EPA 542-R-00-006
Guide to Documenting and
Managing Cost and Performance Information for Remediation Projects -
Revised Version, October, 1998, EPA 542-B-98-007
EPA, 1985. Report
to Congress on Injection of Hazardous Waste, EPA, Office of Drinking Water,
Reeder et al., 1977. Review and Assessment of Deep Well
Injection of Hazardous Waste, Volume I, EPA/600/2-77/029a.
Warner and J.H.Lehr, 1977. An Introduction to the Technology
of Subsurface Wastewater Injection, EPA/600/2-77/240.
Points of Contact:
General FRTR Agency Contacts
Technology Specific Web Sites:
A list of vendors offering
Water Containment Treatment is available from EPA
REACH IT which combines information from three established EPA databases,
the Vendor Information System for Innovative Treatment Technologies (VISITT),
the Vendor Field Analytical and Characterization Technologies System (Vendor
FACTS), and the Innovative Treatment Technologies (ITT), to give users access to
comprehensive information about treatment and characterization technologies and
Health and Safety:
To be added