AREA A/B ENGINEERING REPORT - Waste Management

Geosyntec Consultants
filled and progressively closed (see Figure B-1). After closure, installation of a low-permeability
cover greatly reduces infiltration into a landfill, essentially eliminating the addition of moisture
that causes leachate and LFG generation. Consequently, leachate and LFG generation will cease
over time (Bonaparte, 1995).
LCRS FLOW (lphd)
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0
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7,082
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of Operation
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Figure B-1: Leachate Generation at an MSW landfill in Pennsylvania
(from Othman, et al., 2002)
Note: LCRS = leachate collection and removal system; lphd = liters per hectare per day
The most important limiting factors for leachate and LFG generation rates at a closed landfill are
the design and the condition of the engineered final cover system. For example, in a USEPAsponsored
study of the performance of modern landfills presented by Othman et al. (2002), flow
rates from the leachate collection systems of 11 MSW and 26 hazardous-waste landfill cells
were found to decrease by approximately three orders of magnitude within ten years after
closure with a final cover system that incorporated a geomembrane barrier component (Figure B-
2). Thus, the period for significant leachate and LFG production at a closed landfill with a final
cover system that includes a geomembrane barrier is generally anticipated to be on the order of
tens of years after closure.
Composite liners for Subtitle D landfills consist of a geomembrane upper component and a lowpermeability
soil lower component. The functions of the geomembrane and underlying lowpermeability
soil component are complementary. Acting together, the composite materials
greatly diminish the potential for liner leakage compared to the potential for leakage through a
geomembrane or low-permeability soil layer alone.
MD10186.doc 125 29 March 2009
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