Clay in landfills serves primarily which role?

• A. A material used to cap landfills
• B. A type of waste
• C. A barrier to enhance gas collection
• D. Prevents leachate from contaminating groundwater

Answer: (D)

Clay is used in landfills primarily because it has very low permeability when compacted, making it an effective barrier to liquid movement. This means the clay acts as a liner that slows or stops leachate—the contaminated liquid that forms when rainwater percolates through waste—from migrating into surrounding soil and groundwater.

In practice, compacted clay liners are designed to keep leachate from reaching groundwater, often as part of a multi-layer containment system that may also include synthetic liners. While clay can be involved in caps to reduce infiltration from rainfall, its main purpose in landfill design is to restrict leachate flow. Gas collection relies on other features like venting and gas membranes, so clay’s primary role isn’t to enhance gas collection.