## Facts

- Ontario, joined by U.S. states and environmental organizations, alleged that U.S. emissions were causing acid deposition harming Canada, particularly Ontario.
- Petitioners sought EPA action under Clean Air Act § 115 (International Air Pollution), which can require affected states to revise state implementation plans (SIPs) after EPA makes endangerment and reciprocity findings.
- Petitioners relied in part on a 1981 letter from the EPA Administrator to the Secretary of State stating that U.S. pollutants were endangering public welfare in Canada.
- EPA declined to initiate the § 115 process, asserting it lacked sufficient information to identify the specific U.S. states or source regions whose emissions caused or contributed to the alleged foreign harm.
- EPA interpreted § 115 as an integrated procedure linking findings (endangerment and reciprocity) with notification of the responsible states and ensuing SIP revisions, and therefore viewed action as impracticable without state-level source identification.
- Petitioners sought direct review in the D.C. Circuit of EPA’s denial or non-action on the § 115 rulemaking petition.

## Issues

1. Whether Clean Air Act § 115 requires EPA to initiate the international air-pollution abatement mechanism upon an endangerment finding even if EPA cannot identify the particular source states.
2. Whether EPA permissibly interpreted § 115 as a single integrated process that cannot be initiated in stages separated from the SIP-revision component.
3. Whether EPA’s determination that it lacked adequate information to identify source states, and therefore could not proceed under § 115, was arbitrary, capricious, or contrary to law.

## Decision

- The court denied the petition for review and sustained EPA’s refusal to proceed under § 115.
- The court held that § 115 does not obligate EPA to trigger the statutory mechanism unless EPA can identify the state or states where the relevant emissions originate.
- The court upheld EPA’s “unitary proceeding” interpretation linking endangerment and reciprocity findings with notification and SIP revisions, as a reasonable reading of the statute.
- The court concluded EPA’s explanation—that available information did not permit adequate state-specific source attribution—was not arbitrary or capricious under deferential review.

## Legal Principles

- Where a statutory regulatory mechanism depends on state-specific implementation duties, an agency may reasonably require sufficient identification of the responsible states before commencing the mechanism.
- Clean Air Act § 115 may be construed to integrate (i) endangerment and reciprocity determinations, (ii) notification of the states of origin, and (iii) state SIP revisions; the agency need not initiate the process if it cannot carry it through to effective SIP action.
- Courts will defer to a reasonable agency interpretation of ambiguous statutory text and to the agency’s technical judgment about evidentiary limits relevant to administering the statutory scheme.

## Conclusion

The D.C. Circuit upheld EPA’s refusal to invoke Clean Air Act § 115 for alleged transboundary acid deposition because EPA reasonably interpreted § 115 as requiring identification of the source states before initiating findings and SIP-based remedies, and EPA’s stated inability to make that identification was not arbitrary or unlawful.


Her Majesty the Queen in Right of Ontario v. U.S. Env't Prot. Agency, 912 F.2d 1525 (D.C. Cir. 1990)