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 information. 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.