Double-composite liner systems

The numerical results indicate superior performance of composite liner systems over CCLs in preventing hazardous constituent migration out of the unit and maximizing leachate collection and removal. Consequently, owners of new units subject to the double-liner requirement of FISWA are now installing composite bottom liners or double composite liner systems.3... 

The base liner in modem waste containment facilities is typically a double-composite liner system. Double-composite liner systems are used to contain municipal solid waste and are required for waste containment facilities designed to contain hazardous waste. The primary liner system of a double-composite liner system typically includes a geomembrane and a geocomposite clay liner as the primary barrier layer and a geomembrane underlain by a compacted clay liner composite as the secondary barrier layer. 

A double or triple composite liner system provides maximum protection. 

The minimum prescriptive (regulated) cross sections for liner systems for MSW and HSW disposal in the United States are shown in Fig. 10. As shown in Fig. 10a, the minimum requirements for MSW include a single composite liner overlain by an LCRS. Thus, an LDS and bottom liner are not required for MSW disposal in the United States. However, a double liner system consisting of an LDS sandwiched between a bottom composite liner system and a GML top liner is required in the case of HSW disposal (Fig. 10b). TheLDSandbottomlinerintheHSW requirements provide a level of redundancy in the containment that is required due to the particularly hazardous nature of HSW. 

Clay liners, synthetic liners, or combinations of both are required in landfills. Figure 26.1 depicted the synthetic/composite double-liner system that appears in U.S. EPA s MTG. As explained... 

FIG. 25-77 Schematic of an FML plus composite double-liner system for a landfill. (Drawing not to scale,) (U.S. EPA, EPA/530/SW-85-012, Washington, D.C., 1985. From Freeman, H. M., Standard Handbook of Hazardous Waste Treatment and Disposal, McGratu-Hi//, 1988.)... 

Double-liner systems proposed by the United States Environmental Protection Agency guidelines. The leachate collection layer is also considered to function as the geomembrane protection layer, (a) The flexible membrane liner, FML/composite double liner, (b) FML/compacted soil double liner (after Mitchell, 1986). With the kind permission of the Geological Society. 

The primary characteristic necessary for a liner, cover, or cutoff wall is low permeability, which essentially enables them to slow down the seepage or diffusion of chemicals. Clay is therefore the main material used to construct these containment systems. The thickness and chemical compatibility of containment systems are of concern in assessing the performance of a system. For example, clay liners are constructed as a simple liner that is 2 to 5 ft thick. In composite and double liners, the compacted clay layers are usually between 2 and 5 ft thick, depending on the characteristics of the underlying geology and the type of liner to be installed. Regulations specify that the clay used can only allow water to penetrate at a rate of less than 1.2 in./yr. However, the effectiveness of clay liners can be reduced by fractures induced by freeze-thaw cycles, drying out, and the presence of some chemicals. 

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