• The statutory RQ is one pound for all hazardous substances unless a higher RQ had already been established under the CWA.
• There are special rules that facilities must follow when determining the RQ for releases of mixtures or solutions.

Reportable quantities (RQs)

Congress established reportable quantities (RQs) for hazardous substances that are enforceable until the Environmental Protection Agency (EPA) sets a final RQ for the substance. The statutory RQ is one pound (CERCLA 102(b)) for all hazardous substances unless a higher RQ had already been established under the Clean Water Act (CWA). CERCLA 102(a) gave EPA the authority to adjust the RQs for hazardous substances.

According to 40 CFR 302.5, the quantity listed in the column “Final RQ” for each substance in Table 302.4, or in appendix B to Table 302.4, is the reportable quantity (RQ) for that substance. Whenever the RQs in Table 302.4 and appendix B to the table are in conflict, the lowest RQ shall apply.

In addition, for unlisted hazardous substances designated at 40 CFR 302.4(b), the RQ is 100 pounds. However, unlisted hazardous wastes which exhibit toxicity have the RQs listed in Table 302.4 for the contaminant on which the characteristic of toxicity is based. Review 302.5 for details.

Mixture rule

Most hazardous substances produced, used, or stored by facilities do not exist in pure forms, but are found in mixtures or solutions. There are special rules that facilities must follow when determining the RQ for releases of mixtures or solutions.

If a mixture of hazardous substances is released and the concentration of all hazardous substances in the mixture are known, the Clean Water Act (CWA) mixture rule may be used to calculate whether an RQ of any hazardous substance has been released. RQs of different substances are not additive. This means that spilling a mixture containing half an RQ of one hazardous substance, and half an RQ of another hazardous substance does not add up to trigger reporting requirements.

The release must be reported if the RQ for any hazardous substance has been met or exceeded. If the concentrations of the hazardous substances or extremely hazardous substances (EHSs) are unknown, reporting is required when the total amount of the mixture released equals or exceeds the RQ for the component with the lowest RQ.

The CWA mixture rule can be particularly confusing when applied to Resource Conservation and Recovery Act (RCRA) hazardous wastes. RCRA has identified listed and unlisted waste streams that are regulated as hazardous wastes and thus regulated as the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) hazardous substances. The RQ for each RCRA hazardous waste stream is listed in 40 CFR 302.4. RCRA wastes may be treated as mixtures only if all hazardous components and their concentrations in the mixture are known. Otherwise, the RQ for the waste stream must be used. The CWA mixture rule also applies to unlisted characteristic wastes if the concentrations of all the constituents in the waste are known.

Unlisted wastes exhibiting the characteristics of ignitability, corrosivity, and/or reactivity (ICR) have an RQ of 100 pounds. If a waste known to be hazardous solely because of the characteristic of ignitability was released into the environment, the RQ would be 100 pounds. If an unlisted ICR waste is analyzed and the concentrations of all its hazardous components are identified, the waste is no longer an unlisted waste, but one characterized by its components. Therefore, the RQ of the specific listed components of the hazardous substance can be used to determine when reporting is required.

Toxicity characteristic hazardous wastes (D004-D043) are hazardous substances under CERCLA and are listed with their applicable RQs in Table 302.4 under “Unlisted Hazardous Wastes: Characteristic of Toxicity.” Unlike other unlisted hazardous wastes (ICR), toxicity characteristic hazardous wastes have RQs specific to the contaminant on which the characteristic of toxicity is based (e.g., lead or selenium). If the composition of a waste stream can be determined, then the waste is no longer an unlisted waste, and the CWA mixture rule would apply.