MASONITE CONSTRUCTED A NEW PRODUCT LINE AT ITS FACILITY IN UKIAH, CA. DURING 1989. THE NEW LINE SIGNIFICANTLY INCREASED EMISSIONS OF VOCS AND NOX. MASONITE WAS AN EXISTING MAJOR SOURCE AND ITS CONSTRUCTION OF THE NEW LINE CONSTITUTED A MAJOR MODIFICATION. HOWEVER, MASONITE FAILED TO OBTAIN A PERMIT PRIOR TO CONSTRUCTION, WHICH VIOLATES SECTION 165 OF THE CLEAN AIR ACT. IN ADDITION, MASONITE VIOLATED A PERMIT LIMITATION ON ITS USAGE OF FUEL OIL IN A BOILER ON THE FACILITY.