Supreme Court of the United States

Arkansas v. Oklahoma

February 26, 1992503 U.S. 91

Summary

The Court unanimously held that the EPA acted within its statutory authority in conditioning a federally issued discharge permit on compliance with downstream Oklahoma water quality standards. It did not decide whether the Clean Water Act independently required that compliance. The Act imposed no categorical prohibition on discharges reaching waters already violating water quality standards. The EPA reasonably interpreted Oklahoma’s standards to prohibit detectable degradation, and substantial evidence supported its finding that the permitted discharge would cause no detectable violation. The Court reversed because the Court of Appeals failed to defer appropriately to the EPA’s interpretation and factual findings and improperly substituted its own policy judgment. There were no separate opinions.

Holding

  • EPA authority to require compliance with downstream water quality standards.. The EPA reasonably exercised its statutory authority by requiring the Fayetteville discharge to comply with Oklahoma’s water quality standards; whether the Act itself required that compliance was left unresolved.
  • Categorical prohibition on discharges into already degraded waters.. The Clean Water Act does not categorically prohibit a discharge merely because its effluent would reach waters already violating water quality standards.
  • Interpretation of Oklahoma’s prohibition against degradation.. The EPA’s reasonable, consistently held interpretation that Oklahoma’s standards prohibit actually detectable or measurable degradation was entitled to substantial deference.
  • Judicial review of the EPA’s factual findings and permit issuance.. Substantial evidence supported the EPA’s finding of no detectable violation, and the Court of Appeals improperly displaced the Agency’s findings and deemed its decision arbitrary and capricious.

Docket 90-1262

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