TM 5-814-7
(c) Based upon these calculations, the
70 for grasslands and a steep slope, S > 8 percent.)
design engineer will develop liner panel installation plans
(b) A sedimentation basin will be
with leak detection and leachate collection networks for
established for the landfill construction area; in addition,
the surface impoundment. Design elements will include:
sediment control facilities will be utilized at all temporary
A base grade configuration which slopes at
construction sites.
0.5 percent across the 100-foot width of the
(c) For the active waste area of the
pond, with a crest-to-trough distance of 50
landfill, temporary containment berms can be used to
feet along the pond's 180-foot length to
retain run off for treatment when limited run off volumes
accommodate the leak detection pipe
are involved. By limiting the active waste lift and
network.
containment area for the proposed landfill to an area
Two-inch slotted detection pipes in trenches
about 200 feet long and 100 feet wide, the run off from
over the troughs, with risers up the side
the 100-year storm is 72, 000 gallons. This is based on
slopes within the drainage layer.
100 percent run off from a 5.8-inch intensity rainstorm
A 36-mil reinforced primary synthetic liner.
over the active area.
A 1-foot sand/riprap protective cover.
(d) Due to limited evaporation, the run off
(d) Based upon the calculations outlined
from active areas should be discharged to the surface
above, liner, leak detection and leachate collection
impoundment for subsequent treatment. If no additional
design elements for the landfill include:
rainfall run-off control measures are selected (i.e., tarps,
A base grade configuration which slopes at
restricted operations during rainfall periods), the annual
0.5 percent across the 400-foot width of
rainfall of 39 inches would produce about 500,000
landfill, with crest-to-trough distances of 50
gallons of liquid.
feet along the landfill's length to
(10) Ground-water monitoring wells will be
accommodate the leak detection pipe
installed in accordance with federal regulations, one
network.
hydraulically upgradient of the facility (to provide
A trough along the lower side of the landfill
background water quality data) and three downgradient
to accommodate a collection drainpipe to
to detect contaminant discharge. Well design and
connect leachate laterals to a sump area.
sampling procedures will reflect details presented in
Two-inch slotted detection pipe, as
paragraph 8-3.
described
above
for
the
surface
(11) Special design elements needed for this
impoundment.
facility are impoundment dikes and overtopping controls
A 36-mil reinforced primary synthetic liner.
(part of the plant equipment), with a 2-foot freeboard.
Four-inch slotted leachate collection pipes
Addressed under liner details are requirements for
surrounded with rounded drain rock, within
developing adequate anchor pads for the "over-the-line"
the 1-foot thick drainage layer.
inlet/outlet pipes and appurtenant structures for flow
(8) Gas control measures for the facility will be
control. The only penetrations allowed will be liner
limited to a few pipe vents for the surface impoundment.
"boots" clamped to penetrations for the leak detection
The absence of organic materials below or within the
and leachate collection pipe risers, and gas vents within
landfill and surface impoundments minimizes the
the berm crest of the levee of the surface impoundment
likelihood of air pressure developing below proposed
(see EPA SW-870, figure IV-22, page 371). No wind
liners. Nevertheless, since even a small amount of gas
dispersal provisions will be needed since the ash is
pressure can lift synthetic liners in impoundments,
containerized.
atmospheric pipe vents should be considered at selected
(12) As segments of the fill are brought to final
perimeter locations of the surface impoundment.
grade, final cover for the proposed landfill will be placed
(9) Surface water control features for the
to minimize infiltration of precipitation. As stated in EPA
proposed surface impoundment and landfill will be
SW-870, table V-5, page 267, water balance calculations
similar to those illustrated in figure 5-1. They will include
result in a 2.6-inch maximum monthly infiltration for a 2-
ditches and drainage pipes normally used to prevent flow
foot clay cover. Final cover slopes (selected based on
into active portions of waste units. Upon closure, the
LS factors) will be a minimum 3 percent and 5:1 or less;
run-on control ditches of the landfill carry run off from
assuming proper placement procedures, settlement is
closed final cover areas as well.
not expected to pose a design constraint. The final
(a) Run-on control ditches, V ditches and
cover system will consist of a 20-mil PVC liner placed
the typical trapezoidal ditch shown in figure 6-7, can be
over a 2-foot soil liner (permeability of 1 x 10-7 cm/sec),
constructed with adequate slopes to carry run-off
a drainage layer of sand, and topsoil to facilitate
volumes. For example, with contributory areas of less
vegetative growth. General details for the final cover are
than 5 acres, a peak discharge of less than 20 cfs results
illustrated in figures 6-7 and 6-10.
from the 100-year design storm. (SCS run-off method,
with a type C soil classification, a CN value of
C-5
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