Environmental Glossary of Terms
Leachate

In an environmental context, leachate is considered to be any liquid material that drains from land or stockpiled material and contains significant concentrations of undesirable material, derived from the material through which it has passed.

The most common source of landfill leachate is rainwater filtering down through the different materials within the landfill site. Landfill leachate can be highly toxic, depending upon the characteristic of the materials in the landfill. Previously leachate leaked into the nearby environment, polluting groundwater systems.

Modern landfill sites require the leachate be collected and treated. Since there is no method to ensure that rainwater cannot mix with the waste from the site, landfill sites must now have an impermeable layer at the bottom. The landfill leachate that collects at the bottom must be monitored and treated if necessary. The liquid is then treated, similar to sewage. Older landfill sites where leachate is a problem should be dug up, and either a new impermeable bottom must be installed, or the material must be relocated to another site. However, often this is too late and the damage has already been done to the local environment.

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