Environment
Leachate
Definition
Leachate is the liquid that drains from stockpiled material or land, formed when rainwater, surface water or the waste's own moisture percolates through a landfill body, dissolving and carrying soluble organics, inorganic compounds, heavy metals and xenobiotic organic substances produced by decomposition.
References
Definition, constituent classes, acid vs methanogenic phases, treatment groups
Formation pathways, characteristics, ammonia persistence, treatment technologies
Overview
What it means
Leachate is typically cloudy, brownish, strong-smelling and warmer than groundwater. Its strength changes over the landfill's life: young ("acid phase") leachate is highly concentrated and biodegradable, while older methanogenic leachate is more stable but retains persistent pollutants, notably ammonia, which does not decline with age.
If released untreated, leachate contaminates soil and groundwater, which is why sanitary landfills are engineered with liners and collection systems; treatment combines biological processes, physicochemical steps and membrane technologies such as reverse osmosis.
How it is used
Leachate management is a licensing and monitoring requirement for landfills, a parameter in contaminated-land assessment, and a design driver for waste facilities and mining waste storage.
Why it matters
Uncontrolled leachate is one of the principal pathways by which waste disposal damages water resources and ecosystems.