What Is Hazardous Waste and How to Classify It Correctly

If your sites generate potentially hazardous wastes, it is imperative that you make a hazardous waste determination for each and every waste generated. The Resource Conservation and Recovery Act (RCRA) establishes the framework for determining whether your waste is hazardous and for its proper management. 

To make a proper waste identification, a generator must ask four questions:

1. Is the material a solid waste?

Solid waste is defined under 40 CFR §261.2 as “any garbage or refuse, sludge from a wastewater treatment plant, water supply treatment plant, or air pollution control facility, and other discarded material resulting from industrial, commercial, mining, and agricultural operations, and from community activities.”  The word solid comes from the Solid Waste Act of 1965, and has nothing to do with the physical state (solid, liquid, contained gas) 

However, certain materials are excluded from this definition under §261.4(a) for reasons such as public policy considerations, economic impacts, regulation under other laws, lack of sufficient data, or impracticability of regulation. Examples include domestic sewage, and specific recycled materials. These exclusions are important because they determine whether a material is subject to hazardous waste regulations under RCRA. 

2. Is the waste specifically excluded from RCRA? 

Under §261.4(b), the EPA excludes certain types of solid wastes from the definition of hazardous waste. These materials, even if they meet a listing or exhibit a hazardous characteristic, are not considered hazardous waste. 

Excluded wastes include: 

• Household and agricultural waste – Common non-industrial waste streams.  

• Mining-related materials – Includes overburden and mineral processing wastes (Bevill Amendment).  

•  Energy production byproducts – Fossil fuel combustion wastes (Bevill Amendment) and oil/gas/geothermal wastes (Bentsen Amendment).  

• Industrial residues – Trivalent chromium wastes, cement kiln dust (Bevill Amendment).  

• Treated or contaminated materials – Arsenically treated wood, petroleum-contaminated media from underground tanks.  

• Specific waste streams – Injected groundwater, spent refrigerants (CFCs), used oil filters and distillation bottoms.  

• Landfill byproducts – Leachate and gas condensate. 

Many of these exclusions are conditional and often specific to an industry or waste type. Careful review of these conditions is essential when making hazardous waste determinations to ensure compliance with RCRA regulations. 

3. Is the waste a listed hazardous waste? 

The EPA has studied hundreds of different waste streams and categorized them as hazardous based on their origin and composition. These listed wastes are described in four lists found in 40 CFR Part 261, Subpart D: 

• F List (§261.31) — Wastes from non-specific sources. These are certain solid wastes from common industrial or manufacturing processes that occur across multiple sectors. 
• K List (§261.32) — Wastes from specific sources. These are certain solid wastes generated by 13 specific industries. 
  1. Wood preservation, 
  2. Organic chemicals manufacturing,
  3. Pesticides manufacturing,
  4. Petroleum refining,
  5. Veterinary pharmaceuticals manufacturing,
  6. Inorganic pigment manufacturing,
  7. Explosives manufacturing,
  8. Explosives manufacturing,
  9. Iron and steel production,
  10. Primary aluminum production,
  11. Secondary lead processing,
  12. Ink formulation,
  13. Coking (processing of coal to produce coke)

• P List and U List (§261.33) — Both lists identify pure or commercial-grade formulations of specific unused chemicals as hazardous. The P list includes acutely hazardous chemicals, which are classified this way due to the significant risks they pose to human health and the environment—often causing severe effects such as serious injury or even death. In contrast, the U list contains other hazardous commercial chemical products that are still regulated but are not considered acutely hazardous. 

Listed wastes are considered hazardous by default unless specifically excluded or delisted under RCRA regulations.  

4. Does the waste exhibit a characteristic of hazardous waste?    

Hazardous wastes can be identified by four characteristics defined in 40 CFR §§261.21–261.24. These characteristics indicate how a waste may pose a danger to human health or the environment: 

• Ignitability (D001) — Liquids with a closed cup flash point below (140 °F), certain solids that can ignite, flammable compressed gases, and oxidizers. 

• Corrosivity (D002) — Aqueous waste with pH ≤ 2 (acids) or ≥ 12.5 (bases), or liquids that can corrode steel at a specified rate. 

• Reactivity (D003) — Wastes that are unstable under normal conditions, react violently with water, release toxic gases, or may detonate/explode when heated. 

• Toxicity (D004–D043) —Wastes that leach harmful concentrations of toxic substances when tested using the Toxicity Characteristic Leaching Procedure (TCLP) which could indicate they would leach harmful substances if directly landfilled. 

Any waste exhibiting one or more of these characteristics is regulated as hazardous under RCRA. 

Utilizing the Hazardous Waste Identification Process (HWID) will help ensure you remain EPA-compliant and assist you in properly managing your waste by determining how to store, label, package, transport, and ultimately dispose of or recycle it. 

How can Arcwood help you? 

Did you find this brief explanation of Hazardous Waste Determinations helpful?

Download our our summarized guide here for reference to determine if your waste us hazardous.

Our environmental compliance training programs provide comprehensive instruction for both industry newcomers and experienced professionals. 

Our courses cover the foundations of hazardous waste regulations, generator requirements, and key specialized topics such as: 

• The Generator Improvements Rule 

• The Pharmaceutical Waste Management Rule 

• Aerosols as a Universal Waste 

We ensure every attendee receives the most current, up‑to‑date regulatory compliance training available. 

If you can’t attend one of our in‑person trainings offered throughout the country, we also provide virtual webinars throughout the year—giving you multiple opportunities to stay current and compliant with RCRA training requirements.