RATE OF LEACHATE MIGRATION THROUGH A DEFECT IN A GEOMEMBRANE UNDERLAIN BY A SATURATED PERMEABLE MEDIUM

The leakage collection layer located beneath a geomembrane liner in a landfill may not have enough now capacity to convey the leachate migra ting through a geomembrane defect without becoming filled with leachat e in a certain area around the defect. The presence of leachate in the leakage collection layer at the location of the geomembrane defect re duces the head loss through the defect and, consequently, reduces the rate of leachate migration through the defect. This paper presents an equation to evaluate this effect. The equation depends on the size of the defect in the geomembrane and the characteristics of the leakage c ollection layer: hydraulic conductivity, thickness and slope. Numerica l applications show that the reduction of the leachate migration rate is generally negligible in the case of gravel leakage collection layer s because they are thick and highly permeable. In contrast, with geone t and sand leakage collection layers, there are cases where the reduct ion is not negligible.