ABSTRACT
This chapter describes the state-of-the-art understanding of leachate movement through a landfill, a brief description of mathematical modeling of leachate recirculation, and validation of model results using test cell field data. It shows that moisture moves through the landfill as a vertical wetting front, suggesting that leachate exits from the landfill when the internal storage capacity is exhausted, when the moisture content is at field capacity everywhere. Implementation of leachate recirculation requires an understanding of the effects of leachate recirculation on microbially mediated processes and reactions and of hydrodynamics of leachate flow within a landfill. Leachate is generated primarily as a result of precipitation falling on an active landfill surface, although other contributors to leachate generation include groundwater inflow, surface water runoff, moisture from emplaced waste, and biological decomposition. A US Geological Survey model for Saturated and Unsaturated Flow and transport, Saturated and Unsaturated Flow and Transport was used to model the recirculating landfill.
