ABSTRACT
Adjacent to any centre of population anywhere in the world there is likely to be a landfill site. Many of these sites will have been used because they were in a convenient position or simply because they were available (for example, holes left by gravel, chalk, clay extraction, etc.). Inevitably some of these sites will be in areas where the hydrogeology is such that they pose a threat to groundwater resources and thus remedial action is necessary. Furthermore, developments in landfilling practice, such as daily cover layers and greater compaction of the waste, have tended to reduce the vertical permeability within the landfills. This has promoted horizontal migration of landfill gas, which may need to be controlled. Ironically many carefully operated landfill sites today pose a greater hazard from landfill gas migration than those where the material was deposited more loosely and the gas could escape vertically. This serves to demonstrate that there has always been a crucial lack of information on the behaviour of contaminated sites. Currently, new specifications for landfills are being developed and yet very few landfills have been exhumed to see how man-made barrier materials or even native clays perform in situ.
