## Facts

- Environmental organizations and several states challenged an EPA regulation that excluded “discharges incidental to the normal operation of a vessel,” including ballast water, from Clean Water Act (CWA) National Pollutant Discharge Elimination System (NPDES) permitting.
- EPA had maintained this categorical exclusion since 1973, later reflected in 40 C.F.R. § 122.3(a).
- Ballast water discharges can release “biological materials” and other pollutants into navigable waters, contributing to the introduction of nonindigenous aquatic species and related ecological and economic harms.
- The challenge proceeded through a consolidated petition for review of the rule and an appeal from a district court judgment that invalidated the exemption and ordered EPA to revise its regulation.
- EPA and an industry intervenor defended the exemption as a permissible exercise of EPA authority and argued that other federal programs addressing invasive species supported leaving ballast water outside NPDES.

## Issues

1. Whether the CWA permits EPA to categorically exempt vessel discharges incidental to normal operation, including ballast water, from NPDES permitting.
2. Whether EPA’s definitional or general rulemaking authority allows it to exclude discharges that otherwise satisfy the CWA’s definitions of “pollutant,” “point source,” and “discharge of a pollutant.”
3. Whether the exemption’s long duration and Congress’s failure to overturn it constituted legislative ratification.

## Decision

- The court granted the petition for review and affirmed the district court’s judgment.
- The court held EPA exceeded its statutory authority by exempting incidental vessel discharges, including ballast water, from NPDES permitting.
- The court concluded the exemption was contrary to the CWA’s plain language because vessels are “point sources” and ballast discharges can constitute an “addition” of pollutants (including biological materials) to navigable waters.
- The court rejected reliance on congressional inaction as approval of the exemption.
- The court directed EPA to eliminate the categorical exemption and regulate covered vessel discharges under the NPDES program, allowing for a reasonable implementation schedule.

## Legal Principles

- When statutory text unambiguously covers an activity, an agency may not create categorical regulatory exemptions that conflict with the statute.
- Under Chevron step one, clear CWA definitions of “pollutant,” “point source” (including vessels), and “discharge of a pollutant” foreclose agency interpretations that remove covered discharges from NPDES.
- An agency’s authority to define or implement statutory terms does not permit it to effectively amend Congress’s chosen regulatory scope by excluding categories Congress included.
- Congressional inaction, without clear evidence of focused and affirmative approval, does not override plain statutory requirements.
- Overlapping or supplemental federal regulatory regimes do not impliedly displace the CWA’s permitting mandate absent statutory text to that effect.

## Conclusion

The Ninth Circuit invalidated EPA’s long-standing regulatory exclusion for discharges incidental to the normal operation of vessels, holding that ballast water and similar discharges fall within the Clean Water Act’s NPDES permitting scheme and must be regulated accordingly on a practicable schedule.


Nw. Env't Advocs. v. U.S. Env't Prot. Agency, 537 F.3d 1006 (9th Cir. 2008)