Underground Tank design

Dear:

The standars and examples that I review indicate that the storage underground tank of flammade liquids (Diesel) must have and external filling of sand. However, the there is no posibility to drain this configuration or inspection inside a confinade space. Which is the right configuration in the design?

NFPA 30 and UL 58 refers to the desing of underground tank design. Does Anyoe have both standars to share?

Regards