Biotic barriers

This section describes the elements in a closure or cap system of a completed landfill, including flexible membrane caps (FMCs), SWCR systems, gas control layers, biotic barriers, and vegetative top covers. It also discusses infiltration, erosion control, and long-term aesthetic concerns associated with securing a completed landfill. 

A biotic barrier is a gravel and rock layer designed to prevent the intrusion of burrowing animals into the landfill area. This protection is primarily necessary around the cap but, in some cases, may also be needed at the bottom of the liner. Animals cannot generally penetrate an FMC, but they can widen an existing hole or tear the material where it has wrinkled. 

Figure 26.33 shows the gravel filter and cobblestone components of the biotic barrier and their placement in the landfill system. The proposed 1-m thickness for a biotic barrier should effectively prevent penetration by all but the smallest insects. Note that the biotic barrier also serves as the surface water collection/drainage layer. Biotic barriers used in nuclear caps may be up to 14 ft thick... 

FIGURE 26.33 Optional biotic barrier layer. (Adapted from U.S. EPA, Requirements for Hazardous Waste Landfill Design, Construction, and Closure, EPA/625/4-89/022, U.S. Environmental Protection Agency, Cincinnati, OH, August 1989.)... 

Although the CNS is protected from a number of xeno-biotics by the blood-brain barrier, the barrier is not effective against lipophilic compounds, such as solvents or insecticides (Fig. 7.1). Similarly, the peripheral nervous system is protected by a blood-neural barrier. The barriers are less well developed in the immature nervous system, rendering the fetus and neonate even more susceptible to neurotoxicants. Neural tissue susceptibility is due in large part to its high metabolic rate, high lipid content, and for the CNS, high rate of blood flow. 

Sfeir HA, Reinhart RD, Chopra M, Clausen C, Geiger C. Biotic attentuation and zero-valent iron permeable barrier technology. In Wickramanayake GB, Gavaskar AR, Chen ASC, eds. Chemical Oxidation and Reactive Barriers Proceedings of the Second International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, 20-25 May 2000. Columbus, OH Battelle Press, 2000 C2-6 323-329. 

The average P concentration in the dry matter of terrestrial ecosystems is about 0.2%, whereas that in oceanic ecosystems is about 1.1%. A significant part of this element has been retained in soil humus biogeochemical barrier, where the P content is about 0.15%. The total mass of P in biotic and abiotic matter is about 9.7 x 1 O tons (Table 19). 

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