A working face slope of 3 horizontal to 1 vertical will both minimize
the surface area (and hence minimize the cover material volume) and aid i
compacting the solid waste, particularly if the waste is deposited, then
spread in layers not greater than about 3 feet (0.9 meters) thick and wor
from the bottom of the slope towards the top.
7.4.4.1 Area Method. In this method, the waste is spread and compacted
the surface of the ground, and cover soil is spread and compacted over it
(Figure 16). The area method is used on flat or gently sloping land and
also in quarries, strip mines, ravines, valleys, canyons, or other land
depressions. Cover soil is generally excavated from onsite sources as it
is needed. This is an advantage over the trench method which requires th
much of the cover soil be handled a minimum of two times, a more costly
operation. Advantages and disadvantages of the area method are given in
Table 20.
7.4.4.2 Trench Method. In this method, waste is spread and compacted in
excavated trench (Figure 17). Cover soil, which is taken from the
excavation material, is spread and compacted over the waste to form the
basic cell structure. Usually, cover soil is readily available as a resu
of the trench excavation. Excavated soil not needed for daily cover may
stockpiled and later used as a cover for a subsequent area fill operation
top of the completed trench fill.
In trench designs, the stability of the sidewall is critical. Sidewa
stability, in turn, is determined by the characteristics of the soil,
trench depth, distance between trenches, and slope of the sidewall. Clay
glacial till, and other fine grained, well-compacted soils permit maximum
trench depths, and steep sidewall slopes. With coarser soils, flatter
sidewall slopes are necessary to provide a more stable sidewall. Such
conditions result in correspondingly lower waste volume capacities.
The trench can be as deep as soil and groundwater conditions safely
allow. It should be as narrow as possible to reduce the amount of cover
soil required. Its width is normally dictated by the number and type of
vehicles using the site. Adequate dumping width must be maintained to al
space for delivery truck dumping and maneuverability. In any case, the
trench should be at least twice as wide as any compacting equipment that
will work in it. The equipment at the site may excavate the trench
continuously at a rate geared to landfilling requirements. At small site
excavation may be done periodically on a contract basis in advance of nee
A modification of the trench method involves initial excavation of on
wide trench and subsequent operation perpendicular to the trench axis as
area fill. Soil for daily cover would be excavated from the trench "wall
As the filling progresses, cover soil excavations expand the area availab
for filling so that no new trenches need be excavated.
Advantages and disadvantages of the trench method are given in Table
7.4.5 Environmental Safeguards. Environmental factors that must be
considered in sanitary landfill design (and operation) include those
described below.
5.10-77
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