Approval and Promulgation of Implementation Plans; Arizona Maricopa County CO Nonattainment Area

This action constitutes EPA's response to the Ninth Circuit Court of Appeals' July 31, 1997 opinion in DiSimone versus Browner, No. 96-70974 (9th Cir. July 31, 1997). As a result of the opinion, EPA is restoring the contingency procedures in the carbon monoxide (CO) federal implementation plan (FIP) for the Maricopa County, Arizona nonattainment area (Phoenix) that it promulgated in accordance with Agency guidance issued prior to the 1990 Clean Air Act Amendments (CAAA). EPA is also withdrawing its approval of two contingency measures submitted by the State as revisions, pursuant to the 1990 CAAA, to the CO state implementation plan (SIP) for Phoenix.