Leachate is contaminated liquid that forms when water percolates through landfill waste, picking up dissolved and suspended pollutants. As rainwater and moisture pass through decomposing garbage, they absorb chemicals, heavy metals, and organic compounds, creating a toxic liquid that must be carefully managed. Modern landfills use liner systems to contain leachate and collection pipes to capture it for treatment before disposal. Leachate management is a major environmental consideration in landfill design and operation, with provincial regulations requiring monitoring and treatment systems. Even after landfills close, leachate must be managed for decades as waste continues decomposing.