Leachate Generation Control and Treatment

The best solution to the potential leachate problem is to prevent its development. Landfill leachate generation cannot in practice be entirely avoided, particularly during operation, except possibly in some arid climates. A tight soil cap and/or liner on completion can greatly minimize the possibility; however, a leachate-free landfill may not be entirely desirable. Leachate control measures for groundwa-ter and surface-water quality protection must be incorporated in the site design and monitoring started before operation (see Figure 3.26). A water balance for the landfill disposal facility should be established to serve as a basis for the design of leachate control and surface runoff systems, taking into consideration heavy rainfall, landfill, cap construction, in addition to runoff, infiltration, and evapotranspiration.

Leachate from existing community sanitary landfills and from industrial waste storage and disposal sites can be expected to contain organic and inorganic chemicals characteristic of the contributing community and industrial wastes. Household hazardous wastes may include small amounts of cleaning solvents, paints and paint thinners, oils, pesticides, and drugs if not restricted or their sale prohibited. The EPA and others have reported that hazardous wastes probably represent less than 0.5 percent of the total waste generated by households. A knowledge of the industry and its production will provide a starting point in the selection of parameters to be analyzed in characterizing the leachate from an existing site.

Leachate Generation The precipitation less runoff, transpiration, and evaporation will determine the amount of infiltration. Infiltration and percolation will, in the long term, after field capacity has been reached, determine the amount of leachate, if any, produced, assuming groundwater and lateral flow are excluded. A major factor is a cover material that is carefully graded, which ideally permits only limited infiltration and percolation to support vegetative cover and solid waste decomposition, with optimal runoff but without erosion to prevent significant leachate production. The soil cover should have a low permeability with low swell and shrink tendency upon wetting and drying. Runoff depends on rainfall intensity and duration, permeability of the cover soil, surface slope (4 percent, not greater than 30 percent for side slopes), condition of the soil and its moisture content, and the amount and type of vegetative cover. Evapotranspiration during the growing season for grasses and grains may be 20 to 50 inches.

Diagram Monitoring Well
FIGURE 3.26 Typical monitoring well diagram. (Source: New York State, 6 NYCRR Part 360, Solid Waste Management Facilities, New York State Department of Environmental Conservation, Division of Solid Waste, Albany, 1990a.)

Leachate Control It should be noted that if all infiltration is excluded and the solid waste kept dry, biodegradation by bacteria, fungi, and other organisms will cease and the solid waste will be preserved in its original state. Bacterial activity will generally cease when the moisture content drops below 14 to 16 percent. The maintenance of an optimal amount of moisture in the fill, as in controlled composting (an aerobic process), is necessary for biodegradation (an anaerobic process in a landfill), methane production, final stabilization, and possible future recycling of the solid waste or reuse of the site.

The objective in the design of landfill liners is to minimize or eliminate the infiltration of leachate into the subsurface soils below the landfill so as to eliminate the potential for the groundwater contamination. A number of liner designs have been developed to minimize the movement of leachate into the subsurface below the landfill. One of the many types of liner designs that have been proposed is illustrated in Figure 3.27. In the multilayer landfill liner design illustrated in Figure 3.27, each of the various layers has a specific function. For example, in Figure 3.27, two composite liners are used as a barrier to the movement of leachate and landfill gas. The drainage layer is to collect any leachate that may be generated within the landfill. The final soil layer is used to protect the drainage and barrier layers. The placement of a geomembrane liner in an area-type landfill is illustrated in Figure 3.28. A modification of the liner design shown in Figure 3.27 is shown in Figure 3.29. The liner system shown in Figure 3.29 is for a monofill (e.g., a landfill for a single waste component such as glass). Composite liner designs employing a geomembrane and clay layer provide more protection and are hydraulically more effective than either type of liner alone.

If leachate migration is or may become a problem at an old or existing landfill, and depending on the local situation and an engineering evaluation, several options may be considered. These include a cap on the surface consisting of clay or a liner regraded with topsoil seeded to grass to effectively shed precipitation;

Synthetic liner (60 mil min)

Low permeability soil liner

Synthetic liner (60 mil min)

Low permeability soil liner

Primary Engineering Control Hoods

Primary LCRS

Primary composite liner

Secondary LCRS

Secondary composite liner

10 feet to bedrock

Primary LCRS

Synthetic liner (60 mil min)

Primary composite liner

Low permeability soil liner

Synthetic liner (60 mil min)

Secondary LCRS

Low permeability soil liner

Secondary composite liner

Landfill subgrade

10 feet to bedrock

LCRS = Leachate collection and removal system Composite liner = Synthetic liner + Low permeability soil

FIGURE 3.27 Double-bottom composite liner system. (New York State, 6 NYCRR Part 360, Solid Waste Management Facilities, New York State Department of Environmental Conservation, Division of Solid Waste, Albany, 1990a.)

Geomembrane For Landfills
FIGURE 3.28 Placement of geomembrane liner in area-type landfill.

cutoff walls or dams keyed into an impermeable stratum to isolate the fill; pressure treatment and sealing of the bottom and sides of the fill; surface-water drains up-gradient and around the landfill area; curtain drains or wells to intercept and drain away the contributing groundwater flow, collection and recirculation of leachate with treatment of any excess, or, in special cases and if warranted, the material in the landfill can be excavated, treated, recycled, and/or disposed of at a controlled site. The excavation of an existing landfill may, however, introduce other problems if hazardous wastes are involved and hence must be carefully evaluated in advance.

Leachate Recirculation Waste biodegradation and stabilization of the biodegradable organic matter in a landfill can be accelerated by leachate

Low permeability soil liner

Synthetic liner (60 mil min)

Low permeability soil liner

Synthetic liner (60 mil min)

Single composite liner system

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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  • TYYNE
    How to control leachate from sanitary landfill?
    9 months ago

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