ARIZONA ELECTRIC POWER COOPERATIVE, INC. ( AEPCO ) IS A RURAL ELECTRIC POWER COOPERATIVE THAT PROVIDES ELECTRIC POWER TO COOPERATIVES IN ARIZONA AND CALIFORNIA. AEPCO OWNS AND OPERATES THE APACHE GENERATING STATION NEAR COCHISE, ARIZONA. THE STATION HAS TWO SIMPLE CYCLE GAS TURBINES, ONE COMBINED CYCLE UNIT AND TWO PULVERIZED COAL- FIRED BOILERS. THESE COAL-FIRED BOILERS ARE KNOWN AS UNIT 2 AND UNIT 3. IN SEPTEMBER 1989, REGION IX REQUESTED AUTHORIZATION FROM THE OFFICE OF ENFORCEMENT ( OE ) TO CONDUCT PRE-REFERRAL NEGOTIATIONS WITH AEPCO REGARDING AEPCO'S OPERATION WITH AEPCO'S PRACTICE OF SOOTHBLOWING ACCUMULATED PARTICULATE MATTER FROM UNIT 3 DIRECTLY INTO THE UNIT'S GAS EXHAUST. THIS PRACTICE CONSTITUTES A FAILURE TO OPERATE AND MAINTAIN EQUIPMENT IN A MANNER CONSISTENT WITH GOOD AIR POLLUTION CONTROL PRACTICES FOR MINIMIZING EMISSIONS, AS REQUIRED BY 40 C.F.R. 60.11(D). OE AUTHORIZED PRE-REFERRAL NEGOTIATIONS REGARDING THIS MATTER ON NOVEMBER 1, 1989. THIS NEW REFERRAL RAISES NEW VIOLATIONS BY AEPCO. REGION IX BECAME AWARE OF THESE ADDITIONAL VIOLATIONS DURING A SETTLEMENT MEETING WITH AEPCO REPRESENTATIVES IN DECEMBER 1991. THE VIOLATIONS STEM FROM AEPCO'S FAILURE TO OBTAIN A CLASS B PERMIT BEFORE CHANGING ITS OPERATION OF POLLUTION CONTROL EQUIPMENT ATTACHED TO UNITS 2 AND 3. THE FAILURE TO OBTAIN A CLASS B PERMIT BEFORE MODI