## Facts

- EPA, acting under the Safe Drinking Water Act (SDWA), issued a 1998 final rule setting chloroform’s maximum contaminant level goal (MCLG) in drinking water at 0 parts per billion (ppb).
- EPA historically applied a linear no-threshold assumption for carcinogens, treating zero as the appropriate health goal.
- After EPA’s earlier zero MCLG for chloroform, toxicological and mechanistic evidence developed indicating chloroform’s carcinogenicity followed a threshold (non-linear) mode of action.
- An EPA-convened scientific review panel concluded chloroform would not cause cancer below a certain dose threshold; EPA’s internal assessment contemplated an MCLG around 300 ppb.
- Despite recognizing scientific support for a non-zero MCLG, EPA retained a 0 ppb MCLG, citing the need for further consultation with its Science Advisory Board (SAB) and characterizing the approach as potentially temporary.
- Industry petitioners challenged the rule in the D.C. Circuit, asserting the zero MCLG would likely increase their cleanup obligations and costs under CERCLA by tightening remedial standards derived from drinking-water benchmarks.
- On the day of oral argument, EPA produced a draft SAB report supporting the scientific reasonableness of a low-dose (non-zero) MCLG and moved for vacatur and remand without a merits decision.

## Issues

1. Whether the petitioners had Article III standing based on increased CERCLA cleanup costs, and whether EPA’s request for vacatur and remand mooted the dispute.
2. Whether EPA violated SDWA § 1412(b)(3)(A) by setting a zero chloroform MCLG while acknowledging record evidence supporting a threshold (non-zero) approach as the best available peer-reviewed science.

## Decision

- The court held petitioners had Article III standing because a substantial probability of increased cleanup costs constituted a concrete, fairly traceable injury.
- The case was not moot despite EPA’s request for vacatur because vacatur alone did not ensure adoption of a lawful non-zero MCLG and risked leaving a prior zero MCLG in effect.
- On the merits, the court held EPA unlawfully set the 0 ppb MCLG by overriding the best available scientific evidence indicating a threshold mode of action.
- The court vacated the zero MCLG and remanded to EPA for further proceedings.

## Legal Principles

- When Congress requires regulation based on the “best available, peer-reviewed science,” an agency must base its final rule on the best evidence in the record at the time of decision and may not override it for policy caution or to await possible future studies.
- The possibility that later evidence may contradict current evidence does not justify declining to follow the best currently available science.
- A “range of values” rationale cannot justify selecting zero when the best science supports a threshold, non-zero level.
- An agency cannot avoid statutory scientific obligations by implying a rule is interim; final agency action must satisfy the statute when promulgated.
- In judicial review, vacatur and remand may be ordered where the agency action is contrary to statutory requirements and arbitrary and capricious in light of the agency’s own scientific record.

## Conclusion

The D.C. Circuit vacated EPA’s zero MCLG for chloroform because EPA acknowledged record evidence supporting a non-zero, threshold-based goal yet retained zero pending further deliberation, contrary to the SDWA’s command to use the best available peer-reviewed science.


Chlorine Chemistry Council v. EPA, 206 F.3d 1286 (D.C. Cir. 2000)