## Facts

- EPA issued Clean Air Act (CAA) § 112 MACT emission standards for hazardous air pollutants (HAPs) from primary copper smelters.
- Because metallic HAPs (including arsenic and lead) are emitted largely as particulates, EPA regulated HAP emissions using particulate matter (PM) as a surrogate rather than setting limits for each listed HAP.
- EPA set the MACT standards by reference to performance of the best-performing sources in the category and provided for performance testing, parameter monitoring related to PM controls, and compliance reporting.
- Sierra Club petitioned for judicial review of the final rule under 42 U.S.C. § 7607, challenging the surrogate approach, the monitoring requirements, EPA’s treatment of “non-air quality health and environmental impacts” in beyond-the-floor decisionmaking, and EPA’s timing of Endangered Species Act (ESA) consultation.
- Sierra Club had not participated in the notice-and-comment process, raising exhaustion issues for some objections.

## Issues

1. Whether EPA acted arbitrarily, capriciously, or contrary to CAA § 112 by using PM as a surrogate for metallic HAP emissions from primary copper smelters.
2. Whether EPA’s monitoring and compliance provisions were unlawful or inadequately ensured compliance with the MACT standards.
3. Whether EPA unlawfully construed or failed to consider “non-air quality health and environmental impacts” under § 112(d)(2) when deciding whether to require beyond-the-floor controls.
4. Whether EPA violated the ESA by not completing consultation during the MACT rulemaking rather than in the later residual-risk phase.
5. Whether any challenges were barred because Sierra Club failed to raise them with reasonable specificity during the administrative comment period.

## Decision

- Petition for review denied.
- EPA reasonably used PM as a surrogate for metallic HAPs because the record supported that PM controls reduce the relevant HAP metals and direct HAP-by-HAP limits posed measurement and implementation difficulties.
- EPA’s testing, monitoring, and reporting regime was a lawful compliance approach; the CAA did not compel continuous HAP-specific monitoring in this rule.
- EPA reasonably interpreted “non-air quality health and environmental impacts” to refer to side effects of pollution-control measures, consistent with § 112’s two-phase structure (technology-based MACT first, residual-risk review later).
- EPA permissibly deferred ESA consultation concerns tied to residual risks to the residual-risk phase of § 112 regulation.
- To the extent any objections were not preserved during the administrative process, they were barred; preserved objections did not show the rule was arbitrary or contrary to law.

## Legal Principles

- Under 42 U.S.C. § 7607(d)(9)(A), a CAA rule is set aside only if it is arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law; technical judgments supported by the record receive substantial judicial deference.
- CAA § 112 permits technology-based MACT regulation and can allow use of a surrogate pollutant where the surrogate is scientifically linked to the targeted HAP emissions and provides a rational compliance metric.
- The CAA does not require a particular monitoring technology for MACT standards so long as the monitoring, testing, and reporting framework reasonably assures compliance.
- In setting beyond-the-floor MACT standards, EPA may consider “non-air quality health and environmental impacts,” and reasonable agency interpretations of ambiguous statutory terms are sustained when consistent with the statutory scheme.
- Section 112’s structure separates technology-based MACT controls from later residual-risk evaluation, allowing certain risk-focused inquiries to be addressed in the residual-risk phase.
- CAA issue-exhaustion principles can bar judicial review of objections not raised with reasonable specificity during the public comment process.

## Conclusion

The D.C. Circuit upheld EPA’s MACT standards for primary copper smelters, concluding that EPA’s PM-surrogate limits, monitoring strategy, interpretation of “non-air quality” impacts, and timing of ESA-related consideration were reasonable and lawful under the Clean Air Act’s technology-based first phase and later residual-risk review framework.


Sierra Club v. EPA, 353 F.3d 976 (D.C. Cir. 2004)