Management of Surface Waters

The runoff from the drainage area tributary to the solid waste disposal site must be determined by hydraulic analysis to ensure that the surface-water drainage system, such as ditches, dikes, berms, or culverts, is properly designed and that flows are diverted to prevent flooding, erosion, infiltration, and surface-water and groundwater pollution, both during operation and on completion. The design basis should be the maximum 25-year, 24-hour precipitation. The topography and soil cover should be examined carefully to ensure that there will be no obstruction of natural drainage channels. Obstructions could create flooding conditions and excessive infiltration during heavy rains and snow melt. Uncontrolled flooding conditions can also erode the cover material.

A completed landfill for residential solid waste that is properly capped should, ideally, not present any serious hazard of groundwater pollution, provided surface water (and groundwater) and most of the precipitation are drained, transpired, and evaporated off the landfill and the landfill site. Two different types of landfill covers are presented in Figures 5.36 and 5.37. The major source of water for leachate production would then be precipitation-infiltration during operation, before the final cap is put in place. Precipitation-infiltration can be minimized by the temporary use of impervious geo-membrane sheets over the completed landfill. A small amount of infiltration is desirable to support biological decomposition of the solid waste, as already noted. It becomes essential, therefore, that the solid waste working face be kept at a minimum, that the final cover be placed and graded promptly, and that a surface-water drainage system be installed as soon as possible.

Cover Material The site should preferably provide adequate and suitable cover material. The most suitable soil for cover material is one that is easily worked and

Plan view

Blower/burner facility

Plan view

Gas extraction well

Blower/burner facility e

Area to be protected collection header

Monitoring probe_

Section A-A

Area to be protected

Gas extraction well collection header

Monitoring probe_

Gas collection header

Section A-A

Gas extraction well Control valve —\ \

_Monitoring probe

Gas extraction well Control valve —\ \

Gas collection header

Groundwater < base of landfill

FIGURE 3.34 Typical gas extraction system. (Source: U.S. EPA, Handbook Remedial Action at Waste Disposal Sites, EPA/625/6-85/006, Hazardous Waste Engineering Research Laboratory, Office of Research and Development, EPA, Cincinnati, OH, 1985.)

Groundwater < base of landfill

FIGURE 3.34 Typical gas extraction system. (Source: U.S. EPA, Handbook Remedial Action at Waste Disposal Sites, EPA/625/6-85/006, Hazardous Waste Engineering Research Laboratory, Office of Research and Development, EPA, Cincinnati, OH, 1985.)

yet minimizes infiltration; however, this is not always available. It is good practice to stockpile topsoil for final cover and other soil for cold-weather operation and access road maintenance. Shredded (milled) solid waste in a landfill does not cause odors, rodent or insect breeding, or unsightliness, and it may not require daily earth cover. However, precipitation will be readily absorbed and leachate produced unless the waste is covered with a low-permeability soil that is well graded to shed water.

Typical Landfill Gas Well
FIGURE 3.35 Typical gas extraction well. (Source: U.S. EPA, Handbook Remedial Action at Waste Disposal Sites, EPA/625/6-85/006, Hazardous Waste Engineering Research Laboratory, Office of Research and Development, EPA, Cincinnati, OH, 1985.)

The control of leachate and methane and the role played by the final earth cover, including the importance of proper grading of the landfill final cover (4 percent slope) to minimize infiltration, promote runoff, and prevent erosion, have been previously discussed. A final cover to minimize infiltration of precipitation, support vegetation, and encourage evapotranspiration is recommended. The vegetation, such as seeded grass (hydroseeded for rapid cover), will prevent

2% minimum slope

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