As basic sealing above the geological barrier for hazardous waste landfills, Germany’s “TA-Abfall” (technical instructions on waste management) recommends a combination seal consisting of a 2.5 mm thick plastic sealing membrane pressure-moulded to a mineral seal. In the long run, chlorinated hydrocarbons can permeate through plastic sealing membranes. The permeation rate for HDPE plastics is particularly low, tending toward zero when used in a combination seal. The Contrep sealing system goes beyond the requirements specified in “TA-Abfall” in regard to the following points: multi-mineral base seal instead of a seal composed of only one type of clay, manageable and repairable Contrep system, double-layer plastic sealing membrane instead of single-layer plastic sealing membrane on a mineral seal.