Method of covering the sump of underground cavities

摘要

A method of covering the sump of underground cavities which serve to store gaseous or liquid non-aqueous substances. The sump is covered with a layer of highly viscous crude oil which is at least 1 cm, and preferably 20 to 50 cm, thick. The crude oil contains not more than 7% hydrocarbons having up to 5 C atoms in a molecule thereof. The crude oil has a specific gravity of 20 DEG C. of at most 1.2 g/cm3.