Solute transport through preferential pathways in municipal solid waste

We modelled lithium transport through an undisturbed solid waste sample and a pilot-scale experimental landfill by use of the same probabilistic Lagra ngian approach. The waste sample contained 3.5 m(3) of old, well-degraded w aste, and the experimental landfill 545 m(3) of fresh municipal waste. In t he waste sample, four tracer tests were performed under either constant wat er head or sprinkling input boundary conditions, and either steady state or transient flow. All experimental breakthrough curves (BTCs) exhibit greate r spreading than can be explained by a local dispersion mechanism, even whe n combined with diffusive mass transfer between mobile and immobile water. The observed non-uniform flow and transport could only be represented meani ngfully by a two-domain conceptual model, assuming mobile water and advecti ve solute transport both through preferential flow paths and in zones of sl ow flow. In the undisturbed waste sample, the preferential flow quantificat ion implies that 55-70% of the total infiltrated water moves through only 5 -16% of the total water content. In the landfill, it is 90% of the vertical ly Rowing water that moves preferentially through 47% of the total water co ntent. The difference between the landfill and the waste sample: appears to be: related to waste material properties (which may vary both between and within different waste systems) rather than to the prevailing flow conditio ns (average flow rare or degree of saturation). (C) 2000 Elsevier Science B .V. All rights reserved.