Small quantity generator industries are widely dispersed across the country. Frequently, geographic pockets of small quantity generators representing a collection of industries are concentrated in a few city blocks. While each firm individually generates only a small volume of waste, collectively these firms may constitute "hot spots" of hazardous waste generation. The combined industrial discharge from small firms can potentially upset the chemical or biological treatment processes at publicly owned treatment works (POTWs). While small quantity generators produce only a small volume of waste, their waste is hazardous and must be handled to protect human health and the environment.

GEOGRAPHIC IMPLICATIONS

Next, a look at where hazardous wastes are managed. While most hazardous waste is treated and disposed at the site where it is produced, some hazardous wastes must be transported hundreds of miles to an incinerator or secure landfill. Because waste is shipped interstate, it is important to understand where waste is produced in relation to where it is treated and disposed. For example, some states are net importers of hazardous waste (e.g., Alabama) while other states (e.g., New England states) are net exporters of hazardous waste.

As might be expected, the large majority of hazardous waste is managed in the more highly industrialized areas of the country particularly those areas with active chemical and petroleum industries. An approximate geographic breakdown by the number of Treatment, Storage, Disposal and Recycling (TSDR) facilities, and the volumes of waste managed is provided in Exhibit 4.

Source: National Screening Survey, U.S. EPA, Office of Solid Waste, 1986, and EPA's Hazardous Waste Data Management System.

The Hazardous Waste System includes about 3,000 facilities that treat, store, or dispose of RCRA hazardous waste (see Exhibit 5). In this section the types of treatment typically used are discussed, with particular emphasis on incineration and land disposal technologies.

Source: National Screening Survey, U.S. EPA, Office of Solid Waste, 1986.

Note: Some facilities have more than one process.

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Recycling

Because of economic factors and liability concerns, many firms prefer to store, treat, and dispose of hazardous waste on-site. About 96 percent of all RCRA hazardous waste is managed on-site. The remaining waste is taken off-site to commercial facilities, which are in the business of managing other firms' waste. In addition, significant amounts of industrial wastes are exempt from RCRA regulations but covered under the Clean Water Act. These wastes are typically treated and then discharged to surface waters under an NPDES permit. This section is, however, restricted to the treatment and disposal practices used to manage various types of RCRA hazardous waste.

TREATMENT TECHNOLOGIES

In the Hazardous and Solid Waste Amendments of 1984 (HSWA), treatment technologies are favored over disposal of certain wastes. Treatment refers to any process, including neutralization, designed to change the character of hazardous waste in order to render it less hazardous. Typical treatment methods include incineration, biological and chemical wastewater treatment, steam stripping, and solidification.

The vast majority of the 275 MMT of hazardous waste managed annually is treated in impoundments and wastewater treatment plants. A very small amount of waste, about 2 MMT, is presently incinerated. However, the volume of waste incinerated may increase significantly in response to HSWA requirements. Although most treatment processes reduce the volume or toxicity of waste, there is often a residual that must be further treated or disposed. A waste stream may go through more than one treatment process to reduce its toxicity or volume. The most widely used treatment technologies are briefly described below.

Incineration is used to burn primarily liquid organic hazardous waste. In addition, some incinerators are designed to burn solids and sludges as well as liquid wastes. Increasingly, regulatory decisions favor such practices as incineration over land disposal of certain wastes.

• Biological and Chemical Wastewater Treatment is the most widely used method of treating aqueous hazardous waste. Wastewaters are rendered less hazardous by biological decomposition, chemical neutralization, or precipitation. Treatment occurs in large settling ponds, covered tanks, or impoundments. Retention time in the treatment units varies from a few hours to several days depending on temperatures and the types of waste streams. A residual sludge is produced in the treatment process which is generally incinerated, treated or land disposed.

Steam Stripping technologies are used in treating aqueous, hazardous wastewaters. Hazardous constituents in the water are converted into gas by means of physical treatment. A non-hazardous gas is then emitted into the air and the hazardous constituents are captured through air pollution control equipment.

• Solidification involves mixing a stabilizing agent with hazardous waste to create a solid or impermeable material. The technology requires a large area to combine the stabilizing agent (e.g., Portland cement) with hazardous waste. Solidification is most effectively used on inorganic sludges.