PLUM CREEK, A SAWMILL AND PLYWOOD MANUFACTURING PLANT NEAR KALISPELL, MT. DISCHARGED EMISSIONS INTO THE OUTDOOR ATMOSPHERE EXHIBITING AN OPACITY EXCEEDING FORTY PERCENT (40%) AVERAGED OVER SIX (6) CONSECUTIVE MINUTES, IN VIOLATION OF MONTANA'S AIR QUALITY RULES, WHICH ARE INCORP- ORATED INTO THE EPA APPROVED AND FEDERALLY-ENFORCEABLE STATE IMPLEMENTATION PLAN (SIP). THE VIOLATIONS WERE DOCUMENTED BY A STATE INSPECTOR ON SEPTEMBER 20, 1989 AND AGAIN ON JUNE 13, 1990. ALTHOUGH THE STATE TOOK AN ENFORCEMENT ACTION AGAINST THE SOURCE AND SUBSEQUENTLY SETTLED, THE PENALTY RECEIVED BY THE STATE WAS INADEQUATE. ALSO, THE STATE ACTION DID NOT TAKE INTO ACCOUNT VIOLATIONS WHICH CONTINUED TO OCCUR DURING SETTLEMENT NEGOTIATIONS.