Leachate in landfills: the stability issues

Abstract Of the many technical papers on the quantity of leachate within landfills, almost all of them focus on its generation, collection, removal, or (more recently) on its reinjection for the purposes of accelerated degradation of the waste mass. Few papers have addressed the influence of leachate on the stability of the waste mass, the exception being a few forensic papers dealing with waste failures. Thus, this paper attempts to present a unified approach explaining the influence of leachate on landfill stability in a sequential manner. Moving from relatively low quantities to high quantities, the various leachate distribution scenarios are as follows: (i) discontinuous leachate, (ii) perched or localized leachate, (iii) leachate head on the liner, (iv) leachate head with gas entrapment on the liner, and (v) leachate under excess pore pressure. All these scenarios have the effect of decreasing a given site-specific factor-of-safety (FS) value. Furthermore, the decrease in FS-value is in approximate accordance with the above listing. The various scenarios are illustrated using actual case histories of landfill failures whenever possible. It is shown that the quantity of leachate in a landfill and/or the site-specific liquids management program can be critically important both during waste placement operations and, depending on the geometry of the particular site, quite possibly for the landfill's entire service lifetime with respect to the overall stability of the waste mass.