BACKGROUND AND NATURE OF THE CASE COMMONWEALTH EDISON IS AN ILLINOIS CORPORATION WHICH OWNS AND OPERATES ELECTRIC GENERATING STATIONS. MOST OF COMMONWEALTH EDISON'S STATIONS ARE SUBJECT TO A JUDGMENT ORDER WHICH JUDGE LEIGHTON ENTERED ON JULY 2, 1982. THE JUDGMENT ORDER REQUIRED COMMONWEALTH EDISON TO CONTROL AIR EMISSIONS BY CONSTRUCTING AND OPERATING NEW CONTROL DEVICES AT SOME BOILER UNITS, AND OPERATING OTHER UNITS AT A DERATED BASIS WITH PERIODIC TESTING TO ENSURE THAT COMPLIANCE IS MAINTAINED WITH THE ILLINOIS PARTICULATE AND OPACITY STAND- ARDS. THE JUDGMENT ORDER IN PARAGRAPH 11, REQUIRED COMMON- WEALTH EDISON TO INSTALL A NEW ESP AT THE KINCAID STATION UNIT NO. 1, AND ACHIEVE AND DEMONSTRATE COMPLIANCE WITH ILLINOIS RULE 202 (OPACITY) AND RULE 203(G)(1)(MASS) UPON THE ENTERING OF THE JUDGMENT ORDER, AND INSTALL A NEW ESP AT KINCAID STATION UNIT NO. 2 AND ACHIEVE AND DEMONSTRATE COMPLIANCE WITH THE SAME REGULATIONS BY APRIL 1, 1982. IN ADDITION, PARAGRAPH 9 REQUIRED COMMONWEALTH EDISON TO OPERAT E WILL COUNTY STATION UNIT NO. 4 AT LESS THAN MAXIMUM LOAD AND TO RETEST EVERY SIX MONTHS IN ORDER TO DEMONSTRATE COMPLIANCE WITH RULE 202 AND RULE 203(G)(1). THE SIX-MONTH TESTING CYCLE BEGAN ON JULY 25, 1982. COMMONWEALTH EDISON H AS INSTALLED THE NEW ESP'S AT KINCAID STATION UNITS NO. 1 AND 2 AND HAS ACHIEVED AND DEMONSTRATE