ARIZONA PUBLIC SERVICE OWNS AND OPERATES THE CHOLLA GENERATING STATION NEAR JOSEPH CITY IN NAVAJO COUNTY, AZ. IN 1983, APS MODIFIED ONE OF TIS FOUR COAL-FIRED BOILERS (UNIT 2) MAKING THE UNIT SUBJECT TO NSPS, SUBPART DA AND THE PSD PERMITTING REQUIREMENTS. APS HAS FAILED TO SUBMIT REPORTS AND INSTALL EMISSION MONITORS AS REQUIRED BY SUBPART DA AND HAS FAILED TO OBTAIN A PSD PERMIT PRIOR TO MODIFYING THE FACILITY. IN ADDITION, APS VIOLATED THE ARIZONA STATE IMPLEMENTATION PLAN (SIP) BY OPERATING UNIT 3IN. EXCESS OF THE SO2 EMISSION LIMITS.