How does leachate form in a waste-disposal site?

Leachate is a highly contaminated liquid that forms in waste-disposal sites primarily through two processes:

• Decomposition: As organic material within the refuse undergoes microbial decomposition, it releases liquid by-products.12
• Infiltration: Precipitation (such as rain) or surface runoff infiltrates the waste cells and percolates downward through the volume of garbage. As this water moves through the refuse, it comes into contact with decomposing materials, absorbing contaminants and pollutants along the way.12

If this liquid is not properly managed, it can seep into the ground, potentially contaminating groundwater or nearby surface water, which poses significant risks to public health and the environment. To prevent this, modern sanitary landfills utilize impermeable bottom liners and networks of collection pipes to capture leachate for treatment.123