What is the purpose of liners in landfills?

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Liners in landfills serve as a barrier to keep leachate from reaching groundwater. Leachate is the contaminated liquid that forms when water moves through waste, picking up dissolved substances. If this liquid escapes the landfill, it can pollute nearby soils and drinking water supplies. A liner, made from low-permeability materials such as compacted clay and synthetic membranes, creates a tight barrier at the bottom (and sometimes sides) of the landfill. This barrier is designed to minimize vertical water movement, and it works together with a leachate collection system that removes the liquid for treatment. While liners can influence how gas moves and help contain waste, their primary purpose is to prevent groundwater contamination. The other options describe effects that are not the main function of liners.