What is the minimum depth of suitably graded back fill material that must cover the bottom of the excavation for a fiberglass tank?

The minimum depth of suitably graded backfill material that must cover the bottom of the excavation for a fiberglass tank is typically set at 3 feet. This requirement is based on the need to provide adequate support and protection to the tank, ensuring that it is firmly seated in a stable environment. A depth of 3 feet helps to prevent movement and shifting due to external pressures, such as soil settling, vehicle traffic, or hydrostatic forces, which are particularly critical for fiberglass tanks known for their lightweight and structural characteristics.

Using properly graded backfill material also contributes to the proper drainage around the tank, reducing the risk of water accumulation that could lead to contamination and structural issues. Meeting this depth requirement is a standard practice in UST installations to ensure compliance with safety regulations and long-term durability of the stored fuel.