10 most extreme places on Earth. Landfill leachate is liquid that moves through or drains from a dump or organized trash collection site. Some leachate exists on its own, usually as a result of natural decomposition.liquids and chemicals that have been discarded also contribute.The biggest source of leachate in most places is rainwater, though.0 most extreme places on Earth. Landfill leachate is liquid that moves through or drains from a dump or organized trash collection site. Some leachate exists on its own, usually as a result of natural decomposition.