Classification of Hazardous Chemical Wastes

Management and disposal of many wastes that contain hazardous chemicals are regulated by the U.S. Environmental Protection Agency (EPA) under authority of the Resource Conservation and Recovery Act (RCRA). In the classification system for hazardous chemical wastes specified in 40 CFR Part 261, waste is classified as hazardous by its characteristics or by listing. 

A listed hazardous waste cannot be rendered nonhazardous by treatment or by dilution or mixing with nonhazardous materials. EPAhas issued proposals to establish exemption levels for listed wastes that contain small amounts of hazardous substances, but such exemption provisions are not yet established in regulations. Thus, a listed hazardous waste can be exempted from RCRA requirements only by the process of delisting. EPA also has exempted certain materials that contain hazardous substances to allow their beneficial use (e.g., ash and sludge from coalburning power plants, sewage sludge). 

All wastes classified as hazardous under RCRA, including properly treated toxic waste that is still considered hazardous, are intended for disposal in near-surface facilities regulated under Subtitle C of RCRA. EPA has developed detailed technical requirements on waste treatment and the siting, design, operation, and closure of disposal facilities. Thus, when viewed in relation to intended disposal technologies, there is basically only one class of hazardous chemical waste, regardless of the amounts of hazardous substances present i.e., a waste either is hazardous or it is not. 

Some states (e.g., California, Washington) have defined a category of extremely hazardous waste, and extremely hazardous substances are specified by EPA under the Emergency Response and Community Right-to-Know Act. Under RCRA and state regulations, however, requirements on waste treatment and disposal generally do not distinguish between extremely hazardous waste and any other hazardous chemical waste. 

Requirements on treatment and disposal of hazardous chemical waste under RCRA, especially the intention to limit contamination of groundwater, are based to some extent on considerations of risks to public health and the environment posed by waste. However, requirements on waste treatment and the siting, design, operation, and closure of disposal facilities are not based on long-term projections of the ability of disposal systems to limit releases of hazardous substances to the environment, nor is any consideration given to 

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The states of Washington and California have considered a classification of hazardous chemical waste based on risk and have developed a category of extremely hazardous waste (California, 1999 Mehlhaff et al., 1979 NAS/NRC, 1999b). However, the requirements for treatment and disposal of extremely hazardous waste differ little from those applied to other hazardous waste. Thus, the designation of a class of extremely hazardous waste based on relative hazard has had little effect on waste management and disposal. 

Under current EPA regulations, a chemical waste is either hazardous or it is not, and there is no further classification of hazardous chemical waste with respect to the degree of hazard. Some states have defined classes of hazardous chemical waste (e.g., extremely hazardous waste) but, in practice, the requirements on management and disposal of all hazardous wastes have resulted in essentially the same approaches being used regardless of hazard. When a hazardous chemical waste is mixed with a nonhazardous solid waste, the entire waste is classified as hazardous unless the former is a characteristically hazardous waste that does not contain any listed waste and mixing with the nonhazardous waste removes the hazardous characteristic. 

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