Frequent Questions

Reporting hazardous substance mixtures

How are mixtures of hazardous substances (other than radionuclides) reported?

EPA issued the "mixture rule" (40 CFR section 302.6(b)), developed in connection with CWA section 311 regulations, as a method for determining when to report releases of mixtures or solutions. Under the mixture rule, if the quantities (or concentrations) of all the hazardous constituents of the waste stream are known, notification is required only where an RQ or more of any hazardous constituent is released. However, if the quantity of one or more of the hazardous constituents of the waste is not known, notification is required where the total amount of the waste released equals or exceeds the RQ for the hazardous constituent with the lowest RQ (i.e., the RQ for the waste stream). References 13370 and 13375 provide additional information on how radionuclides are reported.

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