wells may easily range into the hundreds of thousands of
ments, filters, clarifiers, sludge collection, pH control and
several injection pumps.
c. Procedures. Wastes are disposed in injection
wells by injecting waste under pressure to porous
5-6. Waste Piles
injection zones. Following their collection, wastes may
a. Suitable Wastes.
Waste pile storage and
be pretreated and then sent into the pressurized system.
treatment is suitable for semi-solid and solid hazardous
Injection may proceed round the clock, so that large
wastes such as mine tailings. Waste piles may not be
volumes may be disposed of continuously. The injection
used to intentionally dispose of wastes; if disposal is
well system consists of a cased and sealed borehole
required, the owner/operator must obtain a landfill permit
containing the injection tube; wastes are forced through
and manage the pile as a landfill. The regulatory
the tube to the injection zone. Use of a tube for injection
standards for management of waste piles requires that
helps reduce the possibility of leaks; a tube may be
the owner or operator take precautions in treating or
replaced easily, saving wear on borehole casings (see
storing ignitable, reactive or incompatible waste so that it
figure 5-5). All phases of injection are monitored for
does not ignite or explode, emit toxic gases, damage the
leakage detection and proper operation. Disposal
contaminant structure or through other like means
operations are reported quarterly, so corrective action or
threaten human health or the environment. Section
adjustments to the system may be made if necessary.
264.256 prohibits the placement of ignitable or reactive
d. Design elements. UIC regulations require all
wastes in a waste pile, unless the waste is made non-
aspects of injection well systems to be reported and
ignitable or non-reactive. Reactive wastes may be
classified, including construction requirements that
especially difficult to manage since waste piles are
pertain to casing type and cement type, well dimensions,
directly exposed to the environment.
waste characteristics, corrosiveness and leak prevention.
wastes may not be placed on the same waste pile
The regulations also call for tests and logs, including
(section 264.257) to ensure prevention of fires,
electric logs on the injection zone formation and integrity
explosions, gaseous emissions, leaching, or other
of completed wells. In addition, midcourse evaluation of
discharge which could result from the contact or mixing
well performance is required for the first two years of
of incompatible wastes or materials.
In general, all types of materials and
b. Disposal constraints. Waste piles are not an
procedures must be specifically described or referenced.
ultimate disposal method; they are intended only for
As an example, steel and concrete corrosion resistance
storage or treatment of certain solid hazardous wastes.
to the waste stream must be demonstrated.
Given this restriction, the siting criteria for this disposal
e. Equipment needs. Injection well siting and
method are somewhat less stringent that those for
construction requires specialized equipment, material
landfills or surface impoundments. In general, however,
and professional expertise. Well siting requires an
it is preferable that waste piles be located in a
exhaustive review of geology and in-situ formation
hydrogeologic setting that offers sufficient vertical
testing. Injection wells are commonly 1,000 to 5,000 feet
deep; therefore, drilling equipment is needed that is
and low permeability soils providing the hydraulic
capable of reaching that depth. Once the geologic
separation. The precautions concerning location of
environment has been defined, waste compatibility
landfills in karst terrain or seismic zones 3 and 4 also
studies and construction material selection may
pertain to waste piles (see para 5-2b(2)).
c. Procedures. As noted above, a waste pile is any
(1) Since hazardous and corrosive material will
non-containerized accumulation of solid hazardous
be injected, construction materials must be selected that
waste collected for treatment or storage; it is not used to
can handle the waste stream. Concrete mixes and steel
intentionally dispose of wastes.
casing are chosen for their ability to ensure delivery of
depositing wastes in such a unit are therefore quite
waste to the injection zone. Pumps and injection casing
simple: wastes are trucked to the waste pile location,
are also chosen to handle wastes and maintain injection
unloaded, and then placed on the pile.
pressure. The object of design and material selection is
d. Design elements. Basic design requirements for
to choose non-reactive, non-corrosive material to deliver
waste piles include:
and isolate wastes in the injection zone only.
Liners with a leak detection system and
(2) Finally, waste pretreatment may be
necessary prior to injection. One or more types of
Leachate collection and removal
wastes may be injected, so the size and function of the
Run-on and run-off control
facility may vary. Such a surface facility would include
Wind dispersal control
(1) Liners selected for a waste pile must be adequate to