Final answer:
No, existing landfills are not considered sufficient for waste disposal in the foreseeable future due to limited capacity and environmental concerns.
Step-by-step explanation:
Existing landfills are not generally considered sufficient to serve as the sole means of disposing of the nation's waste for the foreseeable future. The two primary methods of waste disposal are landfill and incineration. However, the increased production and disposal of materials, such as plastics which constitute a significant portion of the waste, lead to a situation where landfill capacity may become strained. Landfills do not adequately break down certain materials, and incineration can release harmful toxins into the air. These methods are also tied to issues like groundwater contamination and environmental degradation, indicating a need for more sustainable waste management solutions. Therefore, the reliance on these current methods is likely to be inadequate in the longer term.