Double walled underground storage containers for fluids such as heating oil which endanger the ground water and a method for their manufacture

Claim 1

Double-walled underground storage container for fluids, such as heating oil, which upon leaking are capable of endangering the purity of the ground water, comprising an inner and a surrounding outer wall of synthetic plastic material which define with one another a gap forming a continuous leak monitoring space; a body of open-pore material continuously permeable to air and liquid filling said gap and bracing the inner wall against the outer wall and forming with said walls a homogeneous unit capable of withstanding and absorbing tensile, compressive and torsional forces, said material being synthetic concrete with a compression-resistant structure of filling material having no small components and forming the static load bearing layer of the container, the ratio of synthetic resin present in said synthetic concrete relative to the amount of filling material being such that a sufficient wetting of the particles of said filling material is achieved to assure bonding of said particles to one another but without impairing the permeability of said body; and means for monitoring said space and for detecting pressure variations in the same.