Final answer:
The statement is false as existing landfills are not sufficient for long-term waste disposal due to issues like non-decomposition of certain materials and potential groundwater contamination.
Step-by-step explanation:
The statement that existing landfills are generally considered sufficient to serve as the sole means of disposing of the nation's waste for the foreseeable future is false. The two primary methods of waste disposal in the United States are landfill and incineration.
However, there are significant challenges associated with both methods. Landfills do not decompose certain materials like Styrofoam and plastics, which leads to a risk of groundwater contamination as landfill sites fill up. Improper incineration of these materials adds to air pollution and increases smog. These issues indicate that reliance solely on existing landfills is not a sustainable long-term strategy for waste management.