<< Click to Display Table of Contents >> Navigation:  Appendix A Examples > Example 17: Landfill with Composite Primary Liner > Description

This example demonstrates how to create a landfill with a composite primary liner, primary and secondary leachate collection systems, and a compacted clay secondary liner. The composite primary liner is composed of a 60 mil (1.5 mm) geomembrane in good contact with a 0.9 m thick compacted clay liner. Small holes with an area of 0.1 cm2 and a frequency of 2.5 per hectare (1 per acre) are assumed for the geomembrane. The method proposed by Giroud et al (1992) is used to calculate the flow (leakage) through the composite liner, these calculations are performed automatically by POLLUTE. Below the composite primary liner is a 0.3 m thick granular secondary leachate collection system, overlying a 0.9 m thick compacted clay secondary liner. There is a 3 m thick aquitard under the secondary liner, which overlies a 3 m thick aquifer.

 

The landfill has a length (L) of 200 m in the direction parallel to groundwater flow in the underlying aquifer. Consideration is being given to a volatile organic contaminant with an initial source concentration of 1500 µg/L, which is assumed to remain constant with time over the time period being examined in this example. The leachate head on the composite primary liner is assumed to be constant at 0.3 m, the head on the secondary liner is assumed to be 0.3 m, and the groundwater level relative to the top of the aquifer is assumed to be 3 m (i.e., at the top of the aquitard).

 

The flow in the aquifer must be established based on hydrogeologic data and is represented in terms of the horizontal Darcy velocity (the “Base Outflow Velocity”) in the aquifer at the down-gradient edge of the

landfill (see Example 3 for more discussion of Base Outflow Velocity and Aquifer thickness).

 

The parameters used for this example are listed below: