## Facts

- Congress amended Clean Air Act (CAA) §112 in 1990, creating a technology-based program to regulate hazardous air pollutants (HAPs) through standards for “major sources” and certain “area sources.”
- EPA issued implementing regulations defining key terms and methodologies for determining whether a source is “major,” including:
  - counting fugitive emissions toward the major-source thresholds;
  - treating a “group of stationary sources” located within a contiguous area and under common control as a single source for major-source determinations, without requiring a shared industrial classification;
  - defining “potential to emit” as maximum capacity based on physical and operational design, reduced only by “federally enforceable” limits.
- Multiple industry groups petitioned for review in the D.C. Circuit, challenging portions of the rule as exceeding EPA’s statutory authority under §112.

## Issues

1. Whether EPA could include fugitive emissions when determining whether a source or grouped sources meet §112’s major-source thresholds.
2. Whether EPA could aggregate sources within a contiguous area and under common control without requiring that aggregated units share an industrial classification.
3. Whether EPA could define “potential to emit” to recognize only “federally enforceable” limitations when determining major-source status.
4. Whether other objections raised by certain petitioners to EPA’s §112 implementation rule warranted invalidation.

## Decision

- The court denied the petitions as to challenges brought by National Mining Association, General Electric, and American Forest & Paper Association.
- The court upheld EPA’s inclusion of fugitive emissions in major-source determinations under §112.
- The court upheld EPA’s aggregation approach based on contiguous location and common control without an additional industrial-classification requirement.
- The court granted the petition as to Chemical Manufacturers Association and American Petroleum Institute’s challenge to EPA’s “potential to emit” definition.
- The court set aside the portion of the rule that limited consideration of emissions-limiting conditions to those that were “federally enforceable.”

## Legal Principles

- Under Chevron, when Congress has not directly answered a specific interpretive question in a complex statutory program, a reviewing court will uphold an agency’s interpretation if it is permissible and reasonable in light of the statutory text and structure.
- For CAA §112, EPA may interpret “emits or has the potential to emit” to include fugitive emissions when determining whether major-source thresholds are met, absent a clear statutory prohibition.
- CAA §112’s “major source” definition permits EPA to aggregate stationary sources located within a contiguous area and under common control without imposing an extra industrial-classification limitation not found in the statute.
- EPA may not impose categorical constraints on “potential to emit” calculations that effectively add requirements not supported by §112’s text; limiting relevant emissions-reducing conditions to only “federally enforceable” limits was invalid in this context.

## Conclusion

The D.C. Circuit largely sustained EPA’s core framework for identifying §112 major sources—including counting fugitive emissions and aggregating commonly controlled sources in a contiguous area—but rejected EPA’s attempt to restrict “potential to emit” determinations to federally enforceable limits, setting aside that portion of the rule.


Nat'l Min. Ass'n v. U.S. Env't Prot. Agency, 59 F.3d 1351 (D.C. Cir. 1995)