When a flat site is used for landfilling, the final site surface
generally forms a mound above the surrounding grade. This is done to
optimate filling capacity of the site. The final height of the mound is
generally a function of aesthetics and availability of cover soil. Cover
soil is generally obtained from excavation of onsite soils. The depth an
areal extent of excavation is dependent on several factors including the
ease of soil excavation, the depth to groundwater, and the ultimate heigh
of the fill surface. Unless there is a ready demand for soil at another
location, a balance is made between the volume of cover soil excavated an
the soil required for landfill cover or other onsite uses (e.g.,
construction of a noise control berm). Offsite drainage must also be
diverted around this type of site, especially when filling operations
are being carried out in the excavated area. Figure 14 illustrates a
disposal site constructed in this manner.
Canyon areas offer an ideal location for solid waste disposal provide
that runoff from surrounding slopes is diverted around the disposal area,
thereby preventing washouts, and sufficient soil is available on the cany
bottom and side slopes for use as waste cover, thereby allowing full cany
capacity for solid waste disposal.
7.2.4 Surface Water and Susceptibility to Flooding. Existing bodies of
surface water and water courses on or near proposed sites should be mappe
Current and planned future use of this water should be determined.
Certain areas such as wetlands and floodplains should be avoided whenever
possible. Where it is necessary to construct a sanitary landfill in
either wetlands or floodplains, the proponent should be prepared to
provide for extensive water pollution controls, provide operational contr
of runoff and infiltration, investigate and project environmental
conditions, and allow sufficient time to obtain approvals from regulatory
agencies.
7.2.5 Soil. Soils to be used at a sanitary landfill and the site geolog
should be thoroughly characterized. Ideally, the site should have a
sufficient volume of soil of suitable properties that can be used for all
waste covering (daily, intermediate, and final) throughout the life of th
landfill. Alternatively, soil can be imported from offsite locations, bu
importation can be expensive and off-site soils may not be readily
available.
The ease by which the onsite soil can be excavated is a major
consideration. For example, excavation of bedrock or hardpan is costly,
the material is not well suited for cover. Seasonal variations in
workability should be considered; soils with fines may be easy to excavat
when moist, but may be like hardpan when dry or frozen. Important soil
characteristics such as compaction, drainage, and slope stability are
summarized in Table 12. Soil types will also influence vertical and late
landfill gas migration from the site.
The design engineer must evaluate these design criteria when determin
which soil type or types are best suited for the site's operating and
environmental conditions. For example, in a dry, arid climate where
leachate generation is not a problem, high-permeability soils may be used
for cover. In addition, if there is development around the landfill that
would be adversely impacted by lateral migration of landfill gas,
high-permeability cover soil may be desirable to promote upwards migratio
of gas from the site.
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