·Groundwater contamination: Over time, rainwater mixes with the chemicals from the garbage dumped in the landfill and produces a “leachate”, a sort of toxic sludge that burrows its way down through the landfill and ultimately into the groundwater. (That is, unless there is adequate lining at the landfill’s bottom, which, for older landfills, is seldom present.) The leachate-contaminated groundwater then migrates in whatever direction nature takes it, possibly into a nearby neighborhood’s water supply.
·Methane Gas: The process of compacting landfill waste produces methane-a gas 21 times more potent than carbon dioxide. Methane is most dangerous if it blows out the side of a landfill-under the ground surface-and migrates into a nearby neighborhood, where it can collect in the confined spaces of homes, and create an explosion risk.