Advantages of the composite barrier include very low permeability, high resistance to degradation, the option to install a monitoring system within the membrane, and the ability to isolate and repair sections of the wall without removing the entire membrane envelope. Excavation of the trench is limited by the types of geologic media the particular excavator can tolerate. Backhoes, clamshells, and trenchers are successful in excavating most unconsolidated soils, but clamshells can also remove boulders, if necessary.