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How does an impermeable cap reduce pollution from a completed landfill?

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radioactive waste — hazardous-waste management Employees loading transuranic waste into a shipping container at Vallecitos Nuclear Center, a nuclear research facility in Alameda county, California.

In the context of hazardous-waste management, an impermeable cap is a critical engineering component used to minimize environmental contamination from a completed landfill.

The primary function of the cap is to prevent precipitation and surface runoff from infiltrating the buried waste. By sealing the surface, the cap significantly reduces the amount of water that can percolate through the waste material. This process is essential because it limits the production of leachate—a liquid that forms when water passes through waste and picks up hazardous contaminants.1234

By minimizing leachate generation, the impermeable cap lessens the risk of pollutants migrating into the surrounding soil or contaminating groundwater supplies. These caps are typically constructed using layers of clay, flexible plastic membranes, or a combination of both to ensure a secure, water-resistant barrier.3412