Location restrictions exclude landfills from being near or within certain areas to minimize environmental and health impacts. Table 10.13.1 summarizes location restrictions. Other location restrictions not mentioned in the federal disposal criteria but found in other federal state regulations include public water supplies, endangered or threatened species, scenic rivers, recreation or preservation areas, and utility or transmission lines.
EMISSIONS, LEACHATE, AND MONITORING
Landfills produce gases comprised primarily of methane and carbon dioxide. Emissions are controlled to avoid explosive concentrations of methane or a build-up of landfill gases that can rupture the cover liner or kill cover vegetation. Landfill design and monitoring must ensure that the concentration of CH4 is less than 25% of the lower explosion limit in structures at or near the landfill and less than the lower explosion limit at the landfill property boundary.
A final rule announced by EPA in March, 1996 requires large landfills that emit volatile organic compounds in excess of 50 megagrams (Mg) per year to control emissions by drilling collection wells into the landfill and routing the gas to a suitable energy recovery or combustion device. It also requires a landfill's surface methane concentration to be monitored on a quarterly basis. If the concentration is greater than 500 parts per million, the control system must be modified or expanded to insure that the landfill gas is collected. The rule is expected to effect only the largest 4% of landfills in the United States.
Leachate is water that contacts the waste material. It can contain high concentrations of COD, BOD, nutrients, heavy metals, and trace organics. Regulations require leachate to be collected and treated to avoid ground or surface water contamination. Composite bottom liners are required, consisting of an HDPE geomembrane at least 60 mil over 2 ft of compacted soil with a hydraulic conductivity of less than 1 X 10~7 cm/sec. However, equivalent liner systems can be used, subject to approval. The composite liner is covered with a drainage layer and leachate collection pipes to remove leachate for treatment and maintain a hydraulic head of less than 1 ft. Leachate is generally sent directly to a municipal wastewater treatment plant but can be pretreated, recirculated, or treated on-site.
Leachate generation can be reduced when water is kept from entering the landfill, especially the working face. Surface water control also reduces erosion of the final
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