## Facts

- The dispute concerned EPA regulations under RCRA Subtitle C governing identification and regulation of “hazardous waste.”
- EPA’s regulations included the “mixture rule” (mixtures of listed hazardous waste with other solid waste remain hazardous) and the “derived-from rule” (wastes derived from treatment, storage, or disposal of listed hazardous waste remain hazardous).
- EPA also adopted a “Bevill-mixture rule” addressing mixtures involving certain mineral-processing wastes exempt from Subtitle C by the Bevill Amendment.
- In earlier litigation, the D.C. Circuit vacated the mixture and derived-from rules for failure to satisfy APA notice-and-comment requirements, without deciding whether EPA exceeded its substantive authority under RCRA.
- Because it depended in part on the vacated mixture rule, the D.C. Circuit later vacated and remanded the Bevill-mixture rule as well.
- EPA then issued an interim final rule repromulgating the mixture and derived-from rules and the characteristic-waste portion of the Bevill-mixture rule.
- While industry petitions challenging the reissued rules were pending, Congress enacted the Chafee Amendment, which codified the mixture and derived-from rules by statute and set conditions and deadlines for further EPA action.

## Issues

1. Whether Congress’s enactment of the Chafee Amendment, codifying the mixture and derived-from rules, mooted pending judicial challenges to EPA’s repromulgated rules.
2. Whether any challenges to EPA’s interim action, including aspects of the Bevill-mixture rule or asserted procedural defects, remained justiciable after the Chafee Amendment.

## Decision

- The court dismissed the petitions for review as moot.
- Because intervening legislation superseded the challenged agency rules, the court declined to address petitioners’ substantive and procedural attacks on EPA’s repromulgation.
- The court treated the challenges to the interim Bevill-mixture provision as not presenting a remaining live controversy in light of Congress’s legislative action affecting the regulatory framework.

## Legal Principles

- A case is moot when intervening events eliminate a live controversy such that judicial relief would have no practical effect.
- When Congress codifies the substance of an agency rule by statute, challenges directed at the agency rule may become non-justiciable because the operative obligation arises from legislation rather than the regulation.
- A petition for review of agency action is not a vehicle to invalidate statutory requirements; once the governing rule is statutory, resolving objections to the prior regulation would be advisory.

## Conclusion

The D.C. Circuit held that Congress’s statutory codification of the mixture and derived-from rules eliminated any live dispute over EPA’s repromulgated regulations, requiring dismissal of the industry petitions as moot and leaving the merits of EPA’s RCRA authority unresolved.


Mobil Oil Corp. v. U.S. Env’t Prot. Agency, 35 F.3d 579 (D.C. Cir. 1994)