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This example illustrates the use of the program to model a U.S. RCRA Subtitle D landfill. The landfill consists of a composite liner and a primary leachate collection system. The composite 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 1 per acre (2.5 per hectare) 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 the program.

 

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 liner is assumed to be constant at 0.3 m.

 

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.

 

The parameters used for this example are listed below:

 

 

For more information regarding:

 

• Leakage through composite liners - see Giroud et al (1992).

• Diffusion through geomembranes - see Hughes and Monteleone, (1987); Lord et al (1988).

• Diffusion, sorption, and effective porosity in clays (D, Kd, n) - see Rowe et al (1988)

• Modeling, hydrogeology, and engineering interaction - see Rowe (1992), Rowe et al, 1994.

• Theory used - see Rowe and Booker (1985, 1991), Rowe et al (1994)