I fail to see the corrolation with well compacted imported fill, imported fill, which i assume this is, with the allowable bearing pressure for a storage tank. Unless the tank s very small and the fill is at least 1.5 times the width of it. The settlement and thus 'allowable' bearing pressure would be governed by the material below this layer. Unless you have a extremely highly loaded foundation or applied load that could 'punch' through the fill material. But ive never seen imported fill be the governing, or even usually considered, layer when looking at the alloweable bearing pressure for storage containers or foundations. Only for cases such as large temporary cranes etc.