In the case of Environmental Defense Fund v. Thomas
(870 F.2d 892 (2d Cir. 1989), EPA published a study saying that SO2
emissions (aka acid rain) were a problem. The EPA took no action to revise the
national ambient air quality standards (NAAQSs) to reflect this new
The Appellate Court found that while the court could not
dictate to EPA whether or how the NAAQS should be revised, the Clean
Air Act required EPA to make some decision regarding the revision of
the NAAQS, and that decision, once made, would be judicially reviewable.
Basically, the Court said that EPA must make a decision
when new information comes available, they can't simply ignore it because
it is inconvenient.
Btw, all EPA regulations must be challenged in the D.C.
Circuit because it has special expertise in administrative law matters.