3.5 Solid waste disposal For centuries, chemical wastes have been the by-products of developing societies. Disposal sites were selected for convenience and placed with little or no attention to potential impacts on groundwater quality, runoff to streams and lakes, and skin contact as children played hide-and-seek in a forest of abandoned 55-gallon drums. Engineering decisions here were made by default mlack of planning for handling or processing or disposal at the corporate or plant level necessitated "quick and dirty" decisions by mid- and entry-level engineers at the end of production processes. These production engineers solved disposal problems by simply piling or dumping these waste products "out back." Attitudes eventually began to change and air, water, and land were no longer viewed as commodities to be polluted, with the problems of cleanup freely passed to neighboring towns or future site users. Individuals responded with court actions against polluters, and governments responded with revised local zoning ordinances, updated public health laws, and new major federal clean air and water acts. In 1976, the Federal Resource Conservation and Recovery Act (RCRA) was enacted to give EPA specific authority to regulate the generation and disposal of dangerous and hazardous materials. This chapter discusses the state of knowledge in the field of hazardous waste engineering, tracing the quantities of wastes generated, their handling and processing options through transportation controls, resource recovery, and ultimate disposal alternatives. Over the years, the term hazardous has evolved in a confusing setting as different groups have advocated many criteria for classifying a waste as such. Within the federal government, different agencies use descriptions such as toxic, explosive, and radioactive to label a waste as hazardous. The federal government has developed a nationwide classification system under the implementation of RCRA, in which a hazardous waste is defined by the degree of flammability, corrosivity, reactivity, or toxicity. This definition includes acids, toxic chemicals, explosives, and other harmful or potentially harmful waste. In this chapter, this is the applicable definition of hazardous waste. Radioactive wastes are excluded because, although they obviously are hazardous, their generation, handling, processing, and disposal differ from those of nonnuclear hazards. The radioactive waste problem is addressed separately in Chapter 16. The four criteria for defining hazardous wastemflammability, corrosivity, reactivity, and toxicitymmust be quantified if specific materials are to be included or excluded in the list of hazardous waste. Tests have been developed for rating the flammability of a material by measuring its kindling temperature. Such materials as gasoline are obviously included on this list. Corrosivity is the ability of a chemical to react with common materials, such as sulfuric acid with steel. Reactivity is the propensity of the material to react under normal conditions, such as the reaction of sodium with water. The most difficult criterion to define is toxicity. To define toxicity we need to specify a toxicity to some organism, and how fast, and what effect is considered a toxic effect? Usually it is defined on the basis of effect on humans, although phytotoxicity (damage to plants) and bioconcentration (the ability of the chemical to be concentrated as it moves up the food chain) are equally important. Toxicity to humans is often determined on the basis of experiments on animals, and these results are expressed in terms of the death of the organisms resulting from some high dose of the toxicant.