Containment is used where there is no need to remove the waste material and/or if the cost of removal is prohibitive. The main purpose of containment is to prevent or control liquid or semiliquid contaminated wastes from leaking or leaching into surrounding noncontaminated areas. There are several basic techniques for such purposes including pumping, capping, draining, and the installation of slurry walls. The selection of various types of containment systems is based on the type of waste materials, and geohydrological conditions of the waste site. The role of site characteristics such as those discussed by Wright et al. (1993) and Inyang (1992) in containment system performance is underestimated. Often, more than one containment method is used in a given location. With time, the waste material may slowly biodegrade or chemically change to nontoxic forms or new treatmenl methods may become available for detoxitying the waste. In other words, containment may be used to “buy time” under emergency conditions.