【文章內(nèi)容簡介】 tion stage and the rate of gas generation, and the nature of microbial populations within the waste, amongst other factors. Although many odorous trace pounds may be toxic, they have historically been perceived more as an environmental nuisance than as a direct health hazard (Young and Parker, 1984。 Young and Heasman, 1985). The extent to which odors spread away from the land?ll boundaries depends primarily on weather conditions (wind, temperature, pressure, humidity). Leachate occurrence is by far the most signi?cant threat to ground water. Once it reaches the bottom of the land?ll or an impermeable layer within the land?ll, leachate either travels laterally to a point where it discharges to the ground’s surface as a seep, or it will move through the base of the land?ll and into the subsurface formations. Depending upon the nature of these formations and in the absence of a leachate collection system, leachate has reportedly been associated with the contamination of aquifers underlying land?lls which resulted in extensive investigations for the past four decades (Zanoni, 1972。 Walls, 1975。 Dunlap et al., 1976。 Kelly, 1976。 MacFarlane et al., 1983。 Cheremissino? et al., 1984。 Reinhard et al., 1984。 Ostendorf et al., 1984。 Mackay et al., 1985。 Albaiges et al., 1986。 Mann and Schmadeke, 1986). In fact, it is speculated that in the .,contamination by municipal land?lls, to which every household contributes more than a gallon of hazardous wastes per year (Lee et al.,1986), could bee a bigger problem than contamination associated with the sole disposal of hazardous wastes in land?lls (Senior, 1990). Currently, it is estimated that over 25% of the Superfund sites listed on the National Priority List are solid waste land?lls (Arigala et al., 1995). Although methane and carbon dioxide are the two major ponents of the gas emitted from land?lls, there is evidence that this gas contains numerous other constituents in trace amounts signi?cant enough to cause environmental and health concerns(Lytwynyshyn et al., 1982。 Young and Parker, 1983。 Karimi, 1983。 Gianti et al., 1984。 Harkov et al., 1985。 Todd and Propper, 1985。 Young and Heasman, 1985。 Wood and Porter, 1986。 Rettenberg, 1984, 1987). Potential emissions of Volatile Organic Compounds (VOCs) from land?lls can range from 410?4 to 110?3 kg/m2 /day (US EPA, 1989). Atmospheric gas emission rates through a land?ll cover have been measured by several investigators. During dry soil conditions at a semiarid land?ll site, Bogner et al. (1989) indicated that methane and carbon dioxide ?uxes may be as high as 630 and 950 kg/ m2/yr, respectively. Using ?ux box measurements, Lytwynyshyn et al. (1982) and Kunz and Lu (1979, 1980), estimated that methane di?usion ?ux through land?ll covers ranged between 390 and 1200 kg/m2/yr. These measurements are likely to underestimate actual emission rates because of aerobic oxidation of methane near the surface by methanotrophs. Although emission rates from controlled experiments may not be representative of actual emissions from land?lls, they clearly demonstrate the propensity of gas release into the atmosphere. 5. Land?ll gas and leachate control Land?ll gas control measures are essential in order to eliminate or minimize its associated adverse environmental impacts. In most cases the installation of a gas recovery, collection and treatment system will assist in preventing gas migration away from the land?ll boundaries or gas emissions through the land?ll surface. Indeed many of the early gas recovery projects were developed as a consequence of, or as an adjunct to, existing gas migration control schemes. When land?ll gas is recovered appropriately its methane content represents an energy reservoir of great potential. It is estimated that annual gas generation potential in the US alone exceeds 6 billion m3 (Dawson, 1981。Marchant,1981). The energy represented by this gas could meet 1% of the total energy needs or5% of the natural gas utilization in the . (Lytwynyshyn et al., 1982). Reported estimates of worldwide annual gas generation potential vary widely, 30 to 430 billion m3 (Bingemer and Crutzen, 1987。 Lagerkvist, 1987。 Dessanti and Peter, 1984。 Sheppard et al., 1982). The upper range is questionable, particularly when pared with methane yield data from actual land?lls with a recovery system. The economic feasibility of land?ll gas recovery, processing, and utilization have indeed been demonstrated and reported by many investigators at sites under di?erent climatic conditions (Boyle, 1976。 Lockman, 1979。 Kaszynski et al., 1981。 EMCON, 1983。 Mouton, 1984。 Wiqwist, 1986。 Gendebien et al., 1992). New land?lls can be designed to prevent land?ll gas accumulation even if no productive use of the gas is planned. Land?ll gas control systems have been well documented in engineering practice (Wei