Abstract: A method and apparatus for the subsequent underground sealing of an area, preferably of dumps. With the method, it is possible to seal dumps underground. Working pipes are introduced from a region outside a dump body. The region of soil between the working pipes is loosened, and sealing material is then introduced into this region, which solidifies to become a sheet-like sealing compound. With this method, in particular existing dump bodies can be sealed subsequently underground, without having to drill through the dump body. The apparatus for carrying out the method has a loosening device, and a feed device for the sealing material. The two devices are able to move in the region between two adjacent working pipes.