Listed and Characteristic Waste.

Editor’s Note: Welcome to part 3 in our series about the Resource Conservation and Recovery Act (RCRA). During this series, we’ll guide you through proper hazardous waste handling so you stay compliant and safe.

Facilities that generate solid wastes must make a hazardous waste determination for each waste stream. This is the first critical step in the proper management of hazardous wastes because it determines the facility’s generator status, as well as the regulations that pertain to the handling, storage, treatment and disposal of those wastes.

A waste can be hazardous for several reasons. If a waste has not been specifically excluded from regulation as a hazardous waste [40 CFR 261.4(b)], the two primary considerations for making a hazardous waste determination are:

  • Is it on one of the Environmental Protection Agency’s (EPA) four lists of hazardous wastes?
  • Does it have a hazardous waste characteristic?

RELATED POST: RCRA 101 Part 2: How to Make Hazardous Waste Determinations

The US Code defines a hazardous waste as “a solid waste, or combination of solid wastes, which because of its quantity, concentration, or physical, chemical, or infectious characteristics may cause, or significantly contribute to an increase in mortality or an increase in serious irreversible, or incapacitating reversible, illness; or pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, or disposed of, or otherwise managed” [42 US Code, Chapter 82, Paragraph 6903 Definitions(5)].

From this, the EPA created two broad categories of hazardous waste: listed and characteristic.

Listed Hazardous Waste

A waste becomes a listed hazardous waste when it is fatal to humans in low doses. When toxicity is calculated, one of the factors tabulated is the size of the lowest dose (LD) capable of killing half of a population. This number is expressed as “LD 50.” A listed hazardous waste has:

  • An oral LD 50 toxicity (rat) of less than 50 milligrams per liter
  • A dermal LD 50 toxicity (rabbit) of less than 200 milligrams per kilogram
  • “Is otherwise capable of causing or significantly contributing to an increase in serious irreversible or incapacitating reversible illness” [40 CFR 261.11(a)(2)]

It can also become a listed hazardous waste if it contains any of the hazardous constituents listed in 40 CFR 261, Appendix VIII, and is capable of posing a health or environmental hazard if it is improperly stored, treated, transported, disposed of or managed [40 CFR 261.11(a)(3)].

The EPA has created four lists of hazardous wastes:

  • F-listed wastes are hazardous wastes generated from non-specific sources [40 CFR 261.31]
  • K-listed wastes are hazardous wastes generated from specific sources [40 CFR 261.32]
  • P- and U-listed wastes are discarded commercial chemical products, off-specification species, container residues and spill runoffs [40 CFR 261.33]

An advantage to these lists is that it’s fairly easy for someone with knowledge of their wastes to look at the lists and verify whether or not their waste is on these lists. A disadvantage is that EPA has not been able to test every waste stream ever created, so at times, there may be waste streams that meet the criteria to be listed, but have not yet made it onto a list.

Characteristic Hazardous Waste

Characteristic hazardous wastes are broader categories of waste because they are not dependent upon the name of the chemical or the process from which it was generated. Instead, the focus is on specific qualities of the waste that make it dangerous.

The four qualities that make a solid waste a characteristic hazardous waste are: corrosivity, ignitability, reactivity and toxicity. The EPA chose these four because for each characteristic, succinct, low-cost analytical tests can be used to determine whether or not the waste exhibits a given characteristic.

1. Ignitable wastes [40 CFR 261.21] are the most common type of characteristic hazardous waste. Included are:

  • Liquid wastes with a flashpoint of less than 60°C
  • Solid wastes that cause fire due to friction, absorption of moisture or spontaneous chemical change
  • Ignitable compressed gases
  • Oxidizers

2. Corrosive wastes [40 CFR 261.22] dissolve or corrode flesh, metal or other materials. Included are:

  • Liquids with a pH ≤ 2
  • Liquids with a pH ≥ 12.5
  • Liquids that corrode steel at a rate greater than 6.35 mm per year

3. Reactive wastes [40 CFR 261.23] react violently with water or readily explode. Unlike the other hazardous characteristics, there aren’t succinct analytical tests for reactivity. Included in this category are:

  • Unstable wastes that undergo violent changes without detonating
  • Water-reactive wastes
  • Wastes that form potentially explosive mixtures with water
  • Wastes that generate toxic gases, vapors or fumes when mixed with water
  • Cyanides
  • Sulfides that generate hazardous vapors, fumes or gases when mixed with non-corrosive liquids
  • Wastes capable of detonation
  • Certain explosives

4. Toxic wastes [40 CFR 261.24] are hazardous wastes that are likely to cause health or environmental problems if they leach out of landfills and enter groundwater. A Toxicity Characteristic Leaching Procedure (TCLP) laboratory test is used to determine if the waste contains any of 39 toxic chemicals.


Mixtures of solid and hazardous wastes are handled differently, depending upon which type of hazardous waste has been mixed.

  • Mixtures of solid waste and any amount of a listed hazardous waste must be managed as the listed hazardous waste, regardless of the actual threat that the new mixture poses.
  • A mixture of solid waste and a characteristic hazardous waste is only hazardous waste if the mixture still has a hazardous characteristic.

The EPA also governs any wastes that are derived from the treatment or processing of listed hazardous wastes. These are known as “derived from” wastes and must also be handled as a listed hazardous waste, regardless of their properties. The EPA does provide a few exemptions to the mixture and derived-from rules for certain mining, wastewater and treated process wastes. In addition to the listed exemptions, facilities can petition the EPA to have a waste delisted if they can demonstrate that although it may meet one of the definitions for listing, it does not pose a significant hazard.

Using Generator Knowledge to Make a Waste Determination

While generators are required to properly classify their wastes, they are not required to perform tests if they can make an accurate hazardous waste determination without testing the waste. This is commonly known as “applying generator knowledge” when making a waste determination.

Generator knowledge involves having an understanding of the properties of a waste based on the properties of the chemicals and/or processes that generated the waste. Generators who are able to use their knowledge of chemicals and processes can avoid the expense of testing. Generators without sufficient information on the waste must perform testing [40 CFR 262.11(d)(2)].

The EPA has stated that “the success of the hazardous waste regulatory program depends, to a great extent, on generators making accurate hazardous waste determinations.” Utilizing the EPA’s lists and understanding the properties of wastes generated onsite are tools to help generators make correct determinations and manage their hazardous wastes appropriately.

Up next, learn about waste generator status and requirements for LQGs, SQGs and VSQGs in RCRA 101 Part 4: Determining Waste Generator Status.