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Identification of Hazardous Waste 381
toxicity characteristic. The following wastes are examples of common toxicity characteristic wastes
(40 CFR Part 261.24):

● Paint waste containing metals such as lead, chromium, silver, or cadmium
● Metal strip baths used to remove paint and chrome plating
● Mercury waste from analytical instruments, dental amalgam, and batteries
● Wastewater and sludge from fabric finishing containing tetrachloroethylene
● Oily wastes and sludge from the petroleum marketing industry containing benzene

A solid waste that exhibits the characteristic of toxicity has the EPA Hazardous Waste Number
specified in Table 11.3.
The U.S. EPA has assigned specific hazardous waste numbers and codes to both characteristic and
listed wastes. Each listed hazardous waste will have one or more codes associated with it (Table 11.4).
Many hazardous wastes meet the requirements of more than one waste type. During a waste determi-
nation, all applicable waste codes must be identified and documented.
To summarize, if a solid waste is not a listed hazardous waste and does not exhibit one of the
above four characteristics, it is not in the RCRA system. Even if this is the case, however, the waste
may still be subject to regulation; for example, it may fall under state regulations.

11.3.10 MIXTURES OF HAZARDOUS WASTES WITH OTHER MATERIALS
In addition to a waste being defined as hazardous waste if it is specifically listed or exhibits a haz-
ardous characteristic, a waste is also classified as hazardous if it is: (1) a mixture of a listed haz-
ardous waste and a solid waste (i.e., the mixture rule), (2) a listed hazardous waste contained within
another material (the contained-in rule), or (3) a solid waste generated from the treatment, storage,
or disposal of a listed hazardous waste.

11.3.11 THE MIXTURE RULE
A mixture of any amount of hazardous waste and a solid (nonhazardous) waste is considered a haz-
ardous waste (40 CFR 261.3). There is no de minimis concentration that qualifies for an exclusion
from the mixture rule except for certain mixtures in wastewater treatment systems. For example, if
an employee mixes spent ethyl ether (F003) with an absorbent clay to reduce the liquid content, the
entire mixture is classified as F003.
An exception to the mixture rule is as follows: if the mixture is hazardous solely because it
exhibits a characteristic and the resultant mixture no longer exhibits the same characteristic, it is not
considered a hazardous waste. An example is a paint waste that is an ignitable hazardous waste. A
mixture of the paint waste and a nonignitable, nonhazardous waste (e.g., machine oil) would

TABLE 11.4
Codes for Hazardous Wastes under RCRA
Waste Type EPA Number EPA Code
Ignitable D001 I
Corrosive D002 C
Reactive D003 R
Toxicity characteristic D004–D043 E
Toxic F-, K-, and U-lists T
Acutely hazardous F- and P-lists H
Source: 40 CFR Part 261. With permission.