What must be done when a container is to be abandoned underground?

When a container is to be abandoned underground, it is essential to remove the remaining gas vapor to prevent any potential hazards. Gas vapors can pose significant risks, including the possibility of leaks, explosions, or environmental contamination. Ensuring that the container is free from gas vapors minimizes the likelihood of these dangerous situations arising once the container is buried.

Properly handling gas vapors is a critical step in the decommissioning process of propane containers, as it adheres to safety regulations and best practices in environmental safety. This careful management reflects a responsibility to protect both public safety and the environment.

The other options do not adequately address the critical concern of safety related to gas vapors. Sealing with concrete, filling with water, or leaving the container as is can still leave hazardous gas vapors trapped, which can lead to severe consequences over time. Therefore, removing the remaining gas vapor is the most responsible and safe action to take.