Classification of Hazardous Waste - The Mixture Rule

If a solid waste is mixed with a characteristic hazardous waste through normal laboratory operations, and the mixture retains any hazardous waste characteristic, the entire volume would be considered a hazardous waste.

If a solid waste or characteristic hazardous waste is mixed with a listed hazardous waste, the mixture would require management as the listed hazardous waste. If the listed waste, however, is listed for ignitability, corrosivity, or reactivity, and the mixture no longer exhibits any of these characteristics, then the mixture is not a hazardous waste.

The "Mixture Rule" ( 40 CFR § 261.3a)(2)(iv) ) applies only when you are mixing wastes - not when mixing occurs during a process. Also, mixing wastes to render them nonhazardous is considered treatment. In many cases you need a permit to treat hazardous waste.

Generators should be aware that intentional mixing of waste to change the characteristic, thus avoiding regulation, is in direct violation of RCRA land disposal treatment standards. For a further discussion of improper treatment through dilution, generators are encouraged to reference §268.3, the Dilution Prohibition. Further guidance on this topic can be obtained through Agency memorandum.