Waste Disposal Just over 20 km from Manhattan in New York City lies an enormous monument to the throwaway lifestyle. Fresh Kills (from the Dutch word kil, meaning "stream") is the world's largest landfill and one of the largest structures made by humans. It covers more than 3000 acres of Staten Island and stands more than 150 m high. About half of New York City's garbage-more than 100,000 tons each week-winds up at Fresh Kills. The pile of trash housed in this landfill amounts to more than 25 times the volume of the Great Pyramid at Giza. The site for the landfill was chosen in 1948. It would not be considered geologically appropriate for a modern landfill. The facility is located on what is essentially a salt marsh, with several small streams running through it (between the hills of garbage), and a water table that is very close to the surface. The facility itself was designed without the benefit of pollution control technologies (such as liners, drainage systems, and monitoring stations) that are routinely installed in modern landfills. The high water table under the landfill is problematic, especially in the vicinity of the small streams. The garbage soaks up water, creating a very wet environment within the landfill. The moisture enhances the growth of anaerobic microorganisms (microorganisms that thrive in nonoxygenated environments), which in turn promotes the biodegradation of organic materials in these sections of the landfill. However, it is extremely difficult to determine the chemical composition of the fluids resulting from the decomposition process, and to monitor and control their flow. Before a recent cleanup project was undertaken, it is estimated that more than a million gallons (almost 4 million liters) of contaminated fluids were seeping from the landfill into nearby water bodies each day. Fresh Kills is destined to be filled to capacity by about the year 2000, at which point it will be almost 200 m high. New York City residents will then have to find somewhere else to put their garbage, and try to figure out what to do with the small mountain of urban waste on Staten Island. DISPOSING OF WASTE Virtually every human activity generates waste. Even the simple act of eating results in one of the most challenging waste problems of modern society: sewage. And this doesn't even take into account the wastes generated in the production and transportation of the food that was eaten. Waste disposal is a problem that increasingly demands the attention of scientists, engineers, policy makers, and the general public. This is partly because the volumes of waste are increasing at an alarming rate, and partly because our understanding and appreciation of the hazards associated with improperly handled wastes are growing. The Geology of Waste Management An understanding of geology is fundamental to the management of waste for three reasons: (1) Wastes are generated as a consequence of the use of Earth materials; it is important to understand the properties of these materials, both individually and in combinations. (2) Wastes and contaminants occur in and travel through the geologic environment; we need to understand the nature of this environment and the transport processes. And (3) most waste management schemes involve the use of geologic reservoirs for containment or the use of geologic processes for dilution and dispersal of the waste. As discussed in the essay at the beginning of Part IV, the range of wastes is so vast in terms of sources, chemical characteristics, and physical properties that it is virtually impossible to come up with a simple, all-encompassing categorization scheme. In this chapter we focus on a few types of waste that present significant disposal problems, either because of their sheer volume (e.g., municipal solid waste and sewage) or because of their hazardous characteristics (e.g., toxic and radioactive wastes). Fortunately for this discussion, the range of waste treatment and disposal methods is fairly limited. SOLID WASTE Solid waste, which can be defined very broadly as waste material that cannot be easily passed through a pipe, comprises a very wide range of materials that come from a variety of sources. The primary sources of solid waste are agriculture and mining, followed by industrial and municipal sources. The sources of solid waste, the amount generated at each individual source, and its physical and chemical characteristics are important factors in determining how the waste is handled. Although the difference between a solid and a liquid seems clear enough, the distinction between solid and liquid waste is not always quite so obvious. When solid wastes accumulate, water may pass through and pick up soluble components; as a result, the distinction between solid and liquid waste may become blurred. On the other hand, a waste that is principally in liquid form, such as sewage or fine suspended sediment, may become concentrated into a more or less solid form as a result of treatment procedures or natural settling processes. Agricultural Solid Waste More than half of all solid waste is generated by the agricultural sector, which includes sources like farms, orchards, and animal feedlots. Sediment eroded from fields is one important type of agricultural solid waste. Sediment actually starts out as a liquid waste when it is washed off a field in the form of surface runoff. The eroded sediment can settle and clog adjacent waterways. Also, the soils lost from agricultural lands often carry with them a wide range of chemicals such as pesticides, fungicides, herbicides, and chemical fertilizers, all of which can have damaging effects. Aside from sediment and the associated chemicals, agricultural solid wastes are almost entirely organic. This waste consists primarily of such materials as animal excrement, dead animals, and offal; stubble from fields; prunings from orchards; and other types of plant and animal debris. They are usually disposed of by being allowed to accumulate on-site or washed off into surface waters; only a small fraction of agricultural waste is collected and burned or treated in waste disposal facilities. The disposal of agricultural wastes in surface water bodies, which may become contaminated as a result, is a source of concern, especially in areas where agricultural land is located near population centers. Because of its organic nature, agricultural waste can biodegrade if it accumulates in the right type of environment. Biodegradation is the process whereby the decomposition of a substance is promoted by the action of microorganisms. Biodegradation uses up oxygen, so the main problem associated with organic wastes is the demand placed on the oxygen content of the system in which the material is decaying. If oxygen becomes depleted, it can lead to an excess of organic material in the system, a type of water pollution known as eutrophication. Mine Waste Mining generates a very large volume of waste, virtually all of which is disposed of at the mining or processing site. Some of the solid waste is in the form of piles of discarded rock, or gangue. The volume of a pile of gangue is typically much greater than the original volume of the material underground because the rock is much more compact when it is underground. Another major component of mining wastes is tailings, the slags and sludges that are left behind after processing or smelting. Piles of waste rock and tailings are an eyesore, and the minerals in them may combine with rainwater to form acidic runoff. Dust can blow from the piles and create problems for neighboring communities. The proportion of waste rock to ore depends on the type of mining and the material being sought. For example, relatively little waste is generated in the mining of sands and gravels; most of the material removed is utilized. In the mining of most metallic ores, however, huge quantities of rock must be removed and discarded to obtain a relatively small amount of useful material. For example, a typical copper grade of 2 percent will produce 20 kg of pure metal from each ton of ore processed. In most modern mining operations, piles of waste rock are carefully managed and monitored. If possible, the waste rock is used to fill and grade the mined area and restore the landscape to its pre-mining status. When this is not possible, the piles of waste rock are stabilized by the planting of vegetation, and the land may be used for other purposes, such as forestry or recreation. However, in spite of recent changes in minesite management and site decommissioning, piles of waste rock and tailings at thousands of 'orphaned' minesites pose a major environmental concern. Industrial Solid Waste Industries other than agriculture and mining also generate solid waste, mostly in the form of paper and cardboard products, scrap metal, wood, plastics, glass, yard waste, tires, and rags. Much of this waste comes from small industries, which tend to burn their waste in small incinerators, dispose of it on the site of the plant or factory, or transport it to municipal landfills. Often a substantial tipping fee is charged for disposing of industrial solid wastes in municipal landfills. This is especially true of materials such as wood, which is-in principle-reusable or recyclable. Over the past few years the construction industry has improved recycling rates for wood products, but wood is still a significant component of the rubbish in municipal landfills. Municipal Solid Waste Like most types of waste, municipal solid waste overlaps to a certain extent with other categories of waste. Municipal waste is generally considered to include any solid waste generated by households, small commercial institutions, and light industries. Most of this waste is collected and disposed of by the municipality in which it is generated (or by a contracted collector on behalf of the municipality). In other words, if you put garbage and trash at curbside on garbage collection day and it disappears, or if you haul it to a local disposal facility yourself, it falls in the category of municipal solid waste. Solid waste produced in homes, institutions, and small commercial enterprises actually accounts for a relatively small proportion of the total volume of solid waste, but it presents a major disposal problem for several reasons. Municipal waste is the fastest growing category of solid waste; studies suggest that in some areas the amount of garbage generated per capita has increased by as much as 58 percent since 1960! Another reason for concern is that the bulk of household and commercial waste is generated in areas of high population density, where little land is available on which to dispose of the waste. Finally, environmental and health problems can be caused by municipal wastes that are disposed of improperly, whether in open dumps, inactive landfills, or active landfills that are inadequately engineered. What's in It? Not only the volume-on the order of 400,000 tons per day in the U.S - but also the character of the solid waste generated in towns and cities has changed over the past few decades. Paper, cardboard products, and other packaging materials account for the largest proportion of most landfills (on the order of 35 percent) and are by far the fastest growing component. Household organic material (yard waste and kitchen garbage) is another major component of solid waste in terms of volume. The volumes of non-biodegradable products, such as glass, steel, aluminum, and plastics, have also increased. Used tires, wood, and other waste materials from construction are also found in municipal landfills. Another solid material that must be disposed of is the ashy residue that is left after waste has been burned in an incinerator. Note that some materials take up a lot of room but are quite light. Plastic, for example, constitutes about 18 percent by volume but only 7 percent by weight of municipal solid waste. Other materials, such as glass and metals, are denser, so they weigh more but take up less space. Therefore, if the space remaining in a landfill is the main concern, it may make sense to look at the percentages of each component by volume. If the actual amount of wasted resources is the main concern, the percentages by weight are a better indicator. A potentially serious problem is the presence in municipal landfills of a wide range of toxic chemicals derived from household products. These products range from nail polish to batteries, household and garden pesticides and fertilizers, paints, cleaners, and solvents-many of the products that we rely on and casually throw away in our everyday lives. When many small, seemingly harmless batches of such chemicals accumulate in a municipal landfill, they can add up to a very big toxic waste problem. Source: Murck, B., Skinner, B., and Porter, S. Environmental Ecology. New York: John Wiley & Sons, 1996 (p. 409-13). UPDATE: The Fresh Kills Landfill closed in March 2001.