Much of a buried tank's support is derived from which of the following?

The support for a buried tank primarily comes from compacted backfill. This material plays a crucial role in providing the necessary structural integrity and stability for the tank. When the tank is installed underground, it is surrounded by backfill that has been carefully compacted to ensure that it can effectively support the weight of the tank and withstand the external pressures of the surrounding soil.

Properly compacted backfill helps distribute the load evenly around the tank, reducing the risk of deformation or shifting that could occur if the tank were to settle unevenly. The backfill also helps prevent soil erosion and contributes to the overall safety of the installation.

The other options, while related to the construction and installation of underground storage tanks, do not serve the primary function of providing support in the same way that compacted backfill does. Chain-falls are typically used for lifting and moving heavy objects rather than providing support. Reinforced steel walls can enhance the strength of the tank itself but do not interact with the surrounding soil in the way that backfill does. Concrete may be used in some installations but is not the primary support mechanism for a buried tank. Thus, compacted backfill is essential for ensuring the stability and longevity of underground storage tanks.