ABSTRACT: Protection dams are the most of ten used measures against floods, Their safety is indeed dependent on several factors. One of those factors is the subsoil, too. Slurry wall is the approved measure of subsoil protection. Its construction depends on the impermeable subsoil depth. When bound to the impervious subsoil a doubt can emerge, whether its construction does not interfere groundwater level regime at common or minimum water table, which the paper submitted, deals with.