Agency denial of state petition was arbitrary and capricious, as it didn't state which of four criteria had not been met, or how many of the four criteria must be met to substantiate the petition. Past judicial approval of plan did not insulate it from suit, as it indicated that it was a first step.
Agency plan insufficient, as it relies on a compliance cutoff date after a date previously set by another statute; agency must permit claims that implicate a multi-state area.
Concur: Although claim waived by agency, state's petition impermissibly seeks to regulate single sources as opposed to regulations addressing individual states.