▁purpose : ▁ ▁Fact s ▁Congress ▁am ended ▁the ▁C lean ▁Air ▁Act ▁in ▁ 1 9 7 7 ▁to ▁address ▁states ▁that ▁had ▁failed ▁to ▁att ain ▁the ▁air ▁quality ▁standards ▁established ▁by ▁the ▁Environment al ▁Prote ction ▁Agency ▁( E PA ) ▁( Def endant ). ▁" The ▁am ended ▁C lean ▁Air ▁Act ▁required ▁these ▁' non - att ain ment ' ▁States ▁to ▁establish ▁a ▁permit ▁program ▁reg ulating ▁' new ▁or ▁modified ▁major ▁station ary ▁sources ' ▁of ▁air ▁poll ution ." ▁During ▁the ▁Carter ▁administration , ▁the ▁E PA ▁defined ▁a ▁source ▁as ▁any ▁device ▁in ▁a ▁manufact uring ▁plant ▁that ▁produced ▁poll ution . ▁In ▁ 1 9 8 1 , ▁after ▁Ron ald ▁Re agan ' s ▁election , ▁the ▁E PA , ▁which ▁was ▁head ed ▁by ▁Anne ▁M . ▁G ors uch , ▁adopted ▁a ▁new ▁definition ▁that ▁allowed ▁an ▁existing ▁plant ▁to ▁get ▁perm its ▁for ▁new ▁equipment ▁that ▁did ▁not ▁meet ▁standards ▁as ▁long ▁as ▁the ▁total ▁em issions ▁from ▁the ▁plant ▁itself ▁did ▁not ▁increase . ▁The ▁Natural ▁Resources ▁Def ense ▁Council ▁( NR DC ), ▁an ▁environmental ▁protection ▁group , ▁challeng ed ▁the ▁E PA ▁reg ulation ▁in ▁federal ▁court , ▁which ▁ruled ▁in ▁the ▁NR DC ' s ▁favor . ▁Che v ron , ▁an ▁affected ▁party , ▁appe aled ▁the ▁lower ▁court ' s ▁decision . ▁ ▁Issue ▁The ▁issue ▁facing ▁the ▁Court ▁was ▁what ▁standard ▁of ▁review ▁should ▁be ▁applied ▁by ▁a ▁court ▁to ▁a ▁government