An underground double containment system consists of a concrete outer containment receptacle housing a primary fluid flow pipe, which extends there through and is supported on inverted T-beam structures within the concrete receptacle. The concrete receptacle can be provided with a removable cover providing access to the primary piping in modular sections defined by the boundary of the receptacle and flexible curved tubes opening in the wall of the receptacle through which the primary piping module sections can be removed from the receptacle or held for repair/maintenance.