LANDFILLS When thinking about garbage and its ultimate destination, most people think of a "dump." Traditional open dumps are quite rare today; instead trash is deposited in modern sanitary landfills. The reason for this evolution is that simply dumping garbage in a big pile created several problems. Aside from being unsightly and foul smelling, dumps attracted insects, gulls, rats, and other rodents. These animal "vectors" are harmful to the health of the people living nearby because they can carry disease. Uncontrolled fires, either set or spontaneously combusting, plagued open dumps. The most serious problem resulted from rain percolating through the garbage and carrying harmful bacteria and hazardous chemicals from dumps into groundwater and neighboring ponds or streams. This polluted runoff is called leachate. As a result of these problems, open dumps were banned by the U.S. Environmental Protection Agency (EPA) in 1979, and have been replaced by sanitary landfills. The sanitary landfill concept developed in Great Britain during the 1920s. The procedure entails alternating layers of compacted garbage with clean dirt (sanitary fill) or other material such as compost. Garbage is dumped and then compacted by special bulldozers aptly called "compactors." At the end of each day, after all the garbage has been dumped and flattened, bulldozers cover the fresh layer of garbage with at least six inches of sanitary fill. This process slows decay, prevents exposure to health hazards, and reduces odor problems. Many landfills which have been opened since 1980 are designed to be as safe as possible by installing pollution controls. Some landfills have a liner composed of layers of clay, gravel, or synthetic material to prevent leachate from escaping. Landfills that are "lined" can be fitted with pipes to collect, cleanse, and drain the leachate. Leachate could potentially be recirculated through the landfill, which some tests indicate may speed the decomposition process. Only 11% of existing landfills are lined and have leachate-collection systems. The section of the Central Landfill in Johnston, R.I. which now receives our garbage is lined with three layers and has a leachate collection system. Current EPA regulations require all new landfills be lined and equipped with leachate collection systems. In addition to leachate formation, decomposition is another dynamic occurring in a landfill. Inside a landfill, innumerable microorganisms are hard at work. These microbes may be fungi or microscopic bacteria. Microbes feeding on the organic matter in the landfill transform it into smaller and smaller particles. This rotting or decaying process is called decomposition. Decomposition occurs very slowly in a landfill because there is very little air and moisture (and no sunlight) in the compacted layers of garbage. The lack of these elements mean that even biodegradable materials will take many years to break down. The odor sometimes present at a landfill is caused by the gases created by microorganisms as they break down organic material. Landfill Gas (LFG) is created as a result of the decomposition that is occurring. Left uncontrolled, LFG will migrate out of a landfill and into the atmosphere, creating odor, safety, and environmental problems. LFG is composed of methane (50-55%), carbon dioxide (45-50%), and trace amounts of other gases such as oxygen, nitrogen, and ammonia. The methane component of LFG is of particular concern and must be controlled by the operators of the landfill. Although the gas itself is odorless, it suspends other odors, is highly flammable, and will explode if trapped. Uncontrolled methane has migrated under homes near landfills, which has caused health problems for the residents. There are different systems employed by modern sanitary landfills to vent or collect methane. Some landfills use permeable gravel trenches; others combine a system of pipes with gravel trenches; and others use a pumping system of a connected network of pipes or wells to draw gas out of the landfill. These systems are operated only in portions of landfills that have been closed temporarily or permanently, although they can be installed as the landfill is built and later connected. When LFG is captured it can be burned off in a process called "flaring," or recovered to generate power. Recovering methane for power generation involves drawing LFG out by a huge vacuum. The methane is then cleaned and dried because it is moist when it comes up from the bottom of the landfill. The purified gas then flows through the engines, which work much like a turbocharged car engines. Outside air is filtered in and combined with gas to produce an energy-rich mix. The engines power a huge generator which creates electricity. Only 123 landfills in the country actually collect methane to recover energy. At the Central Landfill we have the largest methane gas recovery and power generating system in the northeast. It generates 12.3 megawatts of electricity, and provides power for 18,000 homes annually. Eventually a landfill reaches its maximum capacity, and cannot accept any more garbage. At this point the landfill must be closed. It is "capped" with a layer of clay and a six-foot layer of earth. Closed landfills have become parks, playing fields, golf courses, and even amphitheaters and ski slopes. The land however, is not suitable for building homes, as it shifts and settles slightly as the waste slowly decomposes. Landfilling is the primary method of municipal solid waste (MSW) management in the United States today. It will continue to be needed for disposing of non-recyclable or non-combustible materials, as well as residual waste from recycling and incineration. Advantages of Sanitary Landfills 1) Landfilling is relatively simple and does not require complex, expensive technology. 2) Landfills are traditional and familiar to governments and the public. 3) Landfills do not "compete" with recycling or source reduction programs. 4) Landfills require fewer permits than incinerators and thus should be faster and easier to site. 5) Energy (methane gas) can be recovered from modern landfills. Disadvantages of Landfills 1) Landfills getting more expensive every year because of required safety regulations and the cost of land. 2) Material in a landfill is so tightly compacted that it degrades very slowly. 3) Runoff from landfills can contribute to groundwater pollution. 4) Recyclable materials buried in a landfill represent a loss of resources. 5) Landfills are encountering the NIMBY syndrome and are becoming increasingly difficult to site. 6) Landfills take up valuable land that could be used for other purposes or left undeveloped as "open space." .