## Facts

- New York City’s Catskill/Delaware drinking-water reservoirs experienced increased phosphorus pollution and eutrophication.
- The Clean Water Act (CWA) requires states to set water quality standards and establish total maximum daily loads (TMDLs) for impaired waters, incorporating seasonal variations and a margin of safety.
- After prior litigation compelled action, New York developed phosphorus TMDLs for eight reservoirs.
- The state expressed the TMDLs as annual phosphorus loads rather than strictly daily loads, and EPA approved them.
- NRDC, Environmental Defense Fund, and the New York City Comptroller challenged EPA’s approval under the Administrative Procedure Act (APA), arguing the CWA required daily loads, the annual approach failed to address seasonal variation, and EPA acted arbitrarily by accepting an aesthetic criterion for phosphorus and a 10% margin of safety.
- The district court upheld EPA’s approval; plaintiffs appealed only the dismissal of their APA challenge to EPA’s approval of the phosphorus TMDLs.

## Issues

1. Whether the CWA requires TMDLs to be expressed strictly as daily loads, or permits approval of TMDLs stated as annual (or other) loads.
2. Whether EPA adequately explained how annual-load phosphorus TMDLs satisfy the CWA requirement to account for seasonal variations.
3. Whether EPA acted arbitrarily and capriciously in approving (a) an aesthetic water quality criterion for phosphorus and (b) a 10% margin of safety.

## Decision

- The Second Circuit affirmed in part and vacated and remanded in part.
- The court upheld EPA’s authority to approve TMDLs expressed in non-daily units, including annual loads, when consistent with effective implementation of water quality standards.
- The court vacated and remanded for EPA to provide a fuller explanation of why annual loads are appropriate for these phosphorus TMDLs and how that choice accounts for seasonal variation.
- The court upheld EPA’s approval of the aesthetic criterion for phosphorus and the 10% margin of safety as not arbitrary and capricious.

## Legal Principles

- The CWA term “total maximum daily load” does not categorically require numerical expression as a daily load; EPA may approve other mass-per-time expressions when reasonable and consistent with the statute’s regulatory purpose.
- When EPA approves a non-daily TMDL, it must give a reasoned explanation showing compliance with the statutory requirement to address seasonal variations.
- Under APA arbitrary-and-capricious review, courts generally defer to EPA’s technical judgments on matters such as selection of water quality criteria and the size of a margin of safety when supported by evidence and reasoned analysis.

## Conclusion

The court allowed EPA flexibility to approve phosphorus TMDLs stated as annual loads, but required EPA to better justify the annual time scale and explain how it accounts for seasonal variation; EPA’s acceptance of an aesthetic criterion and a 10% margin of safety was upheld.


Nat. Res. Def. Council, Inc. v. Muszynski, 268 F.3d 91 (2d Cir. 2001)