Editors' Summary: EPA's rules for determining what substances must be regulated as hazardous waste under RCRA are, to put it mildly, complicated. Understanding these rules, however, is vital, since hazardous wastes are subject to much more complex and costly requirements than nonhazardous solid wastes. Two of EPA's most important rules for determining whether a material will be classified as a hazardous waste are the "mixture" and "derived-from" rules. These two rules are examples of EPA's general policy that once a waste becomes hazardous, it is presumed to remain hazardous regardless of changes in its form or its combination with other substances. The mixture rule provides that any mixture of a listed hazardous waste and a nonhazardous solid waste is itself a RCRA hazardous waste. The derived-from rule states that any waste derived from the treatment, storage, or disposal of a listed waste is deemed hazardous.

This Article discusses EPA's current position on these two rules, analyzes their specific provisions and applications, and discusses the relationship between the two rules and EPA's land ban rules. The Article also discusses the possibility for a de minimis exemption that would exclude wastes that were mixed or derived from hazardous waste if they contained only insignificant quantities of hazardous constituents. The author concludes that these rules are needed in some form to prevent major loopholes in EPA's hazardous waste program. However, EPA may finally be willing to address some of the problems with the rules, including overbreadth and inadequacies in the delisting process.