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 materials is given in Table 4-2-7A, assuming that (1) the cover material is
saturated, (2)a thin layer of water is maintained on the surface, and (3)
there is no resistance to flow below the cover layer.
TABLE 4-2-7A
Theoretical Volume of Water that Could Enter Completed
Landfill Through 1 ft2 of Various Cover Materials in 1 Day
Cover Material
Volume of Water, gal
Uniform coarse sand
9970
Uniform medium sand
2490
Clean, well-graded sand and gravel
2490
Uniform fine sand
100
Well-graded silty sand and gravel
9.7
Silty sand
2.2
Uniform silt
1.2
Sandy clay
0.12
Silty clay
0.022
Clay (30% to 50% clay sizes)
0.0022
Colloidal clay
0.000022
4.2.7.14 Clearly, these data are only theo
can be used in assessing the worst possible situation. icIn actual ,practice ythe
ret al values but the
amount of water entering the landfill will depend on local hydrological
conditions, the characteristics of the cover material, the final slope of the
cover, and whether vegetation has been planted.
4.2.7.15 Among the methods to control the seepage into and out of
landfills are (1) the use of impermeable cover materials, (2) the interception
of high groundwater before it reaches the fill, (3) equalization of the water
levels within and outside the landfill, and (4) the use of an impervious layer
of clay material or other sealants.
4.2.7.16 Conventional Methods for Wet Areas. Recently, because of
concern over the possibility of groundwater contamination by leachate and
gases from landfills and the development of odors, the direct filling of wet
areas is no longer considered acceptable. Installation personnel need to
consult with the state agency before considering disposal in wet areas because
it may be illegal. If wet areas are to be used as landfill sites, special
provisions must be made to contain or eliminate the movement of leachate and
gases from completed cells. Usually this is accomplished by first draining
the site and then lining the bottom with a clay liner or other appropriate
sealants. If a clay liner is used, it is important to continue operation of
the drainage facility until the site is filled in order to avoid the creation
of uplift pressures that could cause the liner to rupture from heaving.
4.2.7.17 Equipment
4.2.7.18 A wide variety of equipment is available from which to
select the proper type and size needed for an efficient operation. The size,
type, and amount of equipment required at a sanitary landfill depends largely
4-57
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