ABSTRACT
Modern landfills will typically incorporate a primary leachate collection system which is intended to control the leachate head (i.e., the height of leachate) on any underlying liner and reduce the potential for advective migration of contaminant. Field observations suggested that collection systems experience a build-up of biofilm, chemical precipitates and small (e.g., silt and sand) particles that are deposited in pipes and the granular material (e.g., sand or gravel) used to drain and collect the leachate generated by a landfill (Brune etal, 1991; Rowe etal,
1995a; Rowe, 1998a,b). This build-up progressively reduces the hydraulic conductivity of the drainage layer and hence its ability to drain the leachate and is called "clogging". However, these same processes that cause "clogging" also represent a form of "leachate treatment" serving to reduce both the organic and inorganic composition of the leachate by a combination of biodegradation and chemical precipitation. Hence the leachate collected at the end of a leachate collection system is not the same as the leachate that entered the system or the leachate that could potentially migrate through the barrier system at locations well away from the collection point. Similar processes can also occur at other leachate collection points, including leachate wells constructed in landfills to reduce leachate mounding (e.g., when other leachate collection is either not present or not effective) and purge wells used to control a leachate plume in the groundwater.
