Abstract: An underground storage tank installation apparatus and method for installing the same. The apparatus includes a fiberglass vault into which one or more underground storage tanks are secured and buried in a suitable excavation. Structural support members are formed within the walls of the fiberglass vault to provide adequate strength for the walls of the fiberglass vault so that the chances of cave-ins are minimized. Internal and external observation wells are provided, with automatic leak detectors, so that any leakage either inside or outside the fiberglass vault is automatically detectable. The preferred method for installing the fiberglass vault is to excavate a pit of predetermined dimensions and pour a concrete base in the bottom thereof. The sides of the pit are lined with sheetrock panels and a liquified fiberglass mixture is sprayed on to the panels and concrete slab, with vertical support members being secured to the sheetrock panels between subsequent layers of the fiberglass coating.