DEEP
WELL INJECTION
Introduction:
Deep well injection is a liquid waste disposal technology. 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.
Description:
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.
Limitations:
Factors that may limit the applicability and effectiveness of these processes
include: