Why Is It Called a Solid Waste — Even When It’s Not Solid?

Author: admin
Date: February 3, 2024

Many people are familiar with the idea that hazardous waste regulations apply to “solid wastes” and understand that this term (confusingly) includes liquids and gases that are (obviously) not solids. But why are they called solid wastes if they’re not solid? 

It’s the way our hazardous waste regulations were written. The Resource Conservation and Recovery Act (RCRA) is the source of all hazardous waste regulation in the U.S. RCRA was enacted in 1976 to update the Solid Waste Management Act of 1965. The act, in Section 1004 (28), defines “solid waste” to include “solid, liquid, semisolid or contained gaseous material …” and, in Section 3001(a), directs the EPA to develop criteria to define “hazardous waste” as a sub-set of this broad definition of “solid waste.” 

The “Notice of Proposed Rule” (NPR) for new EPA regulations (43 FR 58946) explains that the act defined solid waste in this broad manner to capture wastes that are not subject to regulation under Clean Water Act (CWA), Clean Air Act (CAA) or other environmental regulations. This was adopted into U.S. law as 42 USC Section 6903

“The term ‘solid waste’ means any garbage, refuse, sludge from a waste treatment plant, water supply treatment plant, or air pollution control facility and other discarded material, including solid, liquid, semisolid, or contained gaseous material resulting from industrial, commercial, mining, and agricultural operations, and from community activities, but does not include solid or dissolved material in domestic sewage, or solid or dissolved materials in irrigation return flows or industrial discharges which are point sources subject to permits under section 1342 of title 33, or source, special nuclear, or byproduct material as defined by the Atomic Energy Act of 1954, as amended (68 Stat. 923) [42 U.S.C. 2011 et seq.].”

This statutory definition points out that whether a material is a solid waste is not based on the physical form of the material (i.e., whether it is a solid, as opposed to a liquid or gas), but rather that the material is a waste.  

EPA regulations (40 CFR 260.2) expand on that legal definition for hazardous waste determination and define “solid waste” as any material that is discarded and not subject to an exclusion or variance. 

  • “Discarded” means abandoned, recycled, “inherently waste-like” or certain types of military munitions. 
  • “Abandoned” is further defined as disposed of, burned or incinerated, accumulated before being disposed of, or “sham recycled.” 
  • Under the RCRA definition, materials that are recycled (or accumulated before recycling) are (solid) wastes.

Solid wastes (under this RCRA definition) also include materials that are: 

  • “Used in a manner constituting disposal,” meaning applied or placed on land in a manner that constitutes disposal, or used to produce products placed on the land 
  • Burned for energy recovery (or used to produce fuels) 
  • Reclaimed 

Under the RCRA definition, a material cannot be a hazardous waste if it does not meet the definition of a solid waste. Some wastes are explicitly excluded from the definition of “solid waste” and, therefore, are not subject to RCRA Subtitle C hazardous waste regulation, including: 

  • Domestic sewage and mixtures of domestic sewage
  • Irrigation return flow
  • Radioactive waste
  • In-situ mining waste, pulping liquors (if reclaimed) 
  • Spent sulfuric acid (if recycled) 
  • Closed-loop recycling
  • Spent wood preservatives (if recycled) 
  • Scrap metal, shredded circuit boards and certain other materials

Finally, to add to the confusion, not all RCRA solid wastes are regulated. Some solid wastes are excluded from RCRA regulation, including:

  • Household hazardous waste
  • Agricultural waste
  • Mining overburden and certain other mining wastes 
  • Oil, gas and geothermal wastes 
  • Cement kiln wastes 
  • Certain other wastes

Glad you asked? Determining whether a waste is a “solid waste,” as defined under RCRA, and whether that waste is subject to RCRA hazardous waste management requirements are complex tasks that are central components of the hazardous waste management regulations.   

If you have any questions about hazardous waste — solid or not — ACT can help. Please e-mail us at [email protected]. We’re happy to help! 

James Kapin is Principal Advisor for safety, health and environmental compliance for ACTenviro.  Jim is a Certified Industrial Hygienist (CIH) and a Certified Safety Professional (CSP) with over 25 years of workplace safety and environmental protection experience.   Do you have any hazardous waste questions for Jim?  Or any other workplace safety or environmental compliance questions?  Let us know at [email protected]


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