Leachate is a thick liquid that forms when garbage decomposes. At its best, it is similar to very strong sewage water; at its worst, it carries hazardous materials with it that were dissolved from the waste. Newer landfills have synthetic liners above a clay-like soil that help to prevent the leachate from leaking into the groundwater, causing contamination. Older landfills do not utilize this type of liner, and are therefore a threat to our groundwater ¾ especially to nearby neighborhoods.