TM 5-814-7
c. Procedures. Impoundment of hazardous waste
Reuse does not dispose of the waste but can
significantly reduce the quantities requiring disposal.
involves disposing of liquid wastes in a man-made
(g) Addition of Absorbents-Materials can
excavation or diked area that ranges in surface area
be added to aqueous impounded wastes to absorb free
from tenths to hundreds of acres. Wastes are typically
liquids.
Absorbents include fly ash, kiln dust and
delivered to the impoundment by pipe systems or bulk
commercially available sorbents. The designer should
tankers which offload into the impoundment at a
avoid selecting biodegradable absorbents such as straw
"discharge apron."
or rice, since they can decompose, resulting in the
(1) During the time that the liquid wastes are
formation of landfill gas, or contribute to void space,
impounded, operations include, but are not limited to, the
which might lead to subsidence.
following inspection activities:
(3) Cleaning and closure processes normally
Monitoring to ensure that liquids do not rise
involve removal of waste residuals from the
into the freeboard (prevention of overtopping)
impoundment. Removal methods for settled residues
Inspecting containment berms for signs of
and contaminated soil include removal of the sediment
leakage or erosion
as a slurry by hydraulic dredging; excavation of the
Periodic sampling, if needed, of the
sediments with a jet of high-pressure water or air;
impounded wastes for selected chemical
vacuum transport of powdery sediments; or excavation
parameters
of hard solidified sediments by either dragline, front-end
Inspecting periodically for floral and faunal
loader or bulldozer. Sediments removed by one of these
activities (such as animal burrows) that could
methods may require dewatering to comply with EPA
cause leaks through earthen dikes, levees or
guidelines for disposal.
embankments
(4) When residual wastes will be left in the
Monitoring of leak detection systems
impoundment at closure (e.g., the impoundment is used
(2) The major operations at an impoundment
for disposal), the wastes must be stabilized to a bearing
involve "removal" of the liquid waste. There are a
capacity sufficient to support the final cover. Typically,
number of different methods for removing liquid wastes;
stabilization is achieved by either passive (evaporation)
each method must be implemented in accordance with
or active dewatering.
Active processes, including
the standards described in this manual. Waste removal
mechanical dewatering or thermal drying, are described
methods include:
(a) Decanting-Liquids within or ponded on
in EPA SW-873.
d. Design elements. Basic design requirements for
the surface of the impoundment can be removed by
surface impoundments mandated by 40 CFR 264
gravity flow or pumping to a treatment facility if there is
include:
not a large percentage of settleable solids.
(b) Pumping and settling-Liquids or
(1) Double liners with a leak detection system
and monitoring wells to prevent wastes from migrating
slurries composed of suspended or partially suspended
into subsurface soil and ground water and surface water
solids can be removed by pumping into a lined settling
during the active life of the site (see figures 6-2 and 6-5).
pond and then decanting. Sludges are disposed of in a
(2) Prevention of overtopping the sides of the
dry state, and either returned to the impoundment or
impoundment.
disposed of in another contained site.
(c) Solar drying-Liquids are removed by
(3) Construction specifications that ensure the
structural integrity of dikes.
evaporation; sludges remaining after evaporation are left
e. Closure. As specified in 40 CFR 264, a surface
in the impoundment or disposed of in another contained
impoundment can be closed in one of two ways: (1)
site. Note that volatile organics shall not be handled in
Removing or decontaminating all wastes, waste
this manner.
(d) Chemical
residues, system components (such as liners), subsoils
neutralization-Aqueous
and structures or equipment. No post-closure care is
waste with low levels of hazardous constituents
required as long as removal or decontamination is
frequently lends itself to chemical neutralization and
complete.
subsequent normal discharge under NPDES permit
(2) Removing liquid waste or solidifying the
requirements.
remaining waste. A final cover will be placed over the
(e) Infiltration-Certain aqueous waste can
closed impoundment. Post-closure care will consist of
be handled by infiltration through soil, provided that the
monitoring ground-water and conducting corrective
hazardous substances are removed by either soil
action if it is warranted (see para 8-5), and maintaining
attenuation or underdrain collection of the solute.
the effectiveness of the final cover. For a doublelined
Collected solutes are usually treated.
disposal unit, the leak detection system will be monitored
(f) Process reuse-Some aqueous waste
as part of post-closure care.
can be recycled in the manufacturing process a number
of times until the contaminants are at a level requiring
disposal by one of the methods previously mentioned.
5-6
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