Liners

A landfill can be thought of as a bathtub. Liners make the bottom and sides of the landfill less permeable to the movement of water. Figure 10.13.4 shows a typical liner system. Federal regulations call for a composite liner, consisting of an HDPE geomembrane at least 60 mil thick (1000 mil equals one inch) over 2 ft of compacted soil (clay) with a hydraulic conductivity of less than 1 X 10~7 cm/sec. Equivalent or better alternative liner systems are approved in some cases.

Constructing the soil liner requires spreading and compacting impermeable soil in several lifts, ensuring that the soil contains near optimum moisture content and compaction for minimum permeability. Compaction is usually done with large vehicles with sheepsfoot wheels. Synthetic membranes used in composite landfill liners must be at least 60 mil thick. These membranes can be damaged by heavy equipment and are generally protected with a carefully applied layer of sand, soil, or MSW. Geotextiles can also be used to protect geosynthetic liners.

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