What is an acceptable material for filling a container that is to be abandoned underground?

The correct choice of filling material for a container that is to be abandoned underground is both sand and water. This combination is effective because it serves several purposes. First, sand can ensure that the container is adequately filled to prevent any potential collapse, which might be detrimental to the surrounding environment. When used in conjunction with water, sand helps to create a stable medium that minimizes voids and reduces the risk of subsidence.

Water also adds to the effective sealing of the container, preventing the potential migration of pollutants and helping to control any gas release over time. This practice aligns with environmental safety guidelines aimed at minimizing the impact of abandoned structures on soil and groundwater.

While foamed plastic and concrete can serve as fillers in other applications or contexts, they may not provide the necessary stability and sealing capabilities required for underground abandonment. Using just sand alone, although better than other materials, would not be as effective as combining it with water for the reasons mentioned.