When providing a firm foundation for the tank, what type of material should be used in the bed beneath the tank?

In establishing a firm foundation for an underground storage tank (UST), the ideal choice for the material used in the bed beneath the tank is gravel. Gravel provides excellent drainage capabilities, which is crucial for preventing the accumulation of water that could lead to corrosion of the tank or instability of the foundation. It also supports the tank evenly while allowing for air circulation around the base, which can help mitigate potential issues related to soil movement or settling.

While other materials like sand or concrete have their uses, they do not provide the same level of drainage or flexibility. Sand may retain water, potentially leading to issues, and concrete, while strong, does not allow for drainage, which is essential in preventing water-related problems.

The importance of using gravel is highlighted by its ability to create a stable and supportive base for the tank, ensuring that it remains properly anchored and reducing the risk of structural failure or leakage.