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INTRODUCTION

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The past century of industrial, military, and commercial activity worldwide has resulted in hundreds of thousands of hazardous waste sites where organic compounds and metals contaminated surface and subsurface soils, sediments, ground, and surface waters. In order to reduce risks to human and ecologic systems, considerable time and money have been spent remediating these sites since passage of major environmental legislation (e.g., Superfund). Hazardous waste management is undoubtedly one of the most important environmental issues. Despite the common agreement that industrial production without waste is our long-term goal, there will be an ongoing need for proper management of wastes for years to come. Further, there is a need to continue to sharpen the cause and effect relationships between a polluted environment and poor public health. These relationships resulting from exposure to hazardous wastes are more insidious and subtle manifestations in children and adults. The challenge is to better understand these contaminants, and to determine under which conditions and at which levels they pose a threat to human health and the environment.

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DEFINITIONS OF WASTE

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Classifications and Properties of Waste

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Wastes may be classified by their physical, chemical, and biological characteristics. An important classification criterion is their consistency. Solid wastes are waste materials having less than approximately 70% water. This class includes municipal solid wastes such as household garbage, industrial wastes, mining wastes, and oil-field wastes. Liquid wastes are usually wastewaters, including municipal and industrial wastewaters, that contain less than 1% suspended solids. Such wastes may contain high concentrations (greater than 1%) of dissolved species, such as salts and metals. Solid waste, as defined under the Resource, Conservation, and Recovery Act (RCRA) is any solid, semisolid, liquid, or contained gaseous material discarded from industrial, commercial, mining, or agricultural operations and from community activities. Solid waste includes garbage, construction debris, commercial refuse, and sludge from water supply or waste treatment plants, material from air pollution control facilities, and other discarded materials. Solid waste does not include solid or dissolved materials in irrigation return flows or industrial discharges. Sludge is a class of waste intermediate to solid and liquid wastes. Sludge usually contain between 3% and 25% solids, while the rest of the material is water-dissolved species. These materials, which have a slurry-like consistency, include municipal sludge, which is produced during secondary treatment of wastewaters, and sediments found in storage tanks and lagoons.

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Federal regulations classify wastes into three different categories, based on hazard criteria: (a) nonhazardous, (b) hazardous, and (c) special. Nonhazardous wastes are those that pose no immediate threat to human health and/or the environment, for example, municipal wastes such as household garbage and many high-volume industrial wastes. Hazardous wastes are of two types: (a) those that have characteristic hazardous properties, that is, ignitability, corrosively, or reactivity, and (b) those that contain leachable toxic constituents. Other hazardous wastes include liquid wastes, which are identified with a particular industry or ...

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