servation and Recovery Act. These wastes are now regulated and must be separated from other wastes and managed in special facilities. Wastes must exhibit at least one of the following characteristics to be considered hazardous: ignitability, corro-sivity, reactivity, and toxicity. Most hazardous wastes come from industries but a small portion is generated in normal household solid wastes. Workers of the Garbage Project at the University of Arizona found a relationship between socioeconomic characteristics of neighborhoods and the composition of hazardous waste: low-income households produce more car-care items (such as motor oil and gas additives); middle-income households produce more items associated with home improvement (such as paints, stains, and varnishes); and upper-income households produce more lawn and garden items (such as pesticides and herbicides) (Rathje and Murphy, 1992). Nuclear waste provides a special case of the highest priority in terms of safety (Weber and Wiltshire, 1985). The proposed approach taken for these materials is geological disposal, where wastes are buried under very thick layers of soil and rock (Carter, 1987). However, risks remain with geological disposal (Shrader-Frechette, 1993), and the technology for nuclear waste management is still evolving. Current debate focuses on the Yucca Mountain, NV, site near Las Vegas which is scheduled to be the world's first geologic repository for high-level nuclear waste (Apted et al., 2002; Ewing and MacFarlene, 2002).

Under current conditions there is little opportunity for ecological engineering to contribute to landfill technology. The systems by necessity are dominated by conventional engineering designs and procedures. The best opportunities may come for leachate treatment, and Mulamoottil et al. (1999) describe constructed wetlands for this purpose. Also, Beeby (1993) suggests that methane (i.e., biogas) production from landfills can be optimized, but "the ecosystem itself has to be managed to favour the methanogenic bacteria." This kind of management theoretically is possible, but it is unlikely to occur for practical reasons.

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