I have a storage tank (leg supported) within a concrete containment area. The floor of the contaiment area will serve as the "Footing" for the tank legs. I have seen calculations by others that state the soil pressure under a matt foundation is 10,000 psf at a site that has an allowable soil pressure of 1500 psf for a typical footing design. Is the fact that the tank (one of 4 in the same containment) is on a large matt foundation warrant 6 times increase in the soil pressure? Is there some reference? Thank you in advance.