NATURE OF CASE CATERPILLER TRACTOR OWNS & OPERATES A GREY-IRON FOUNDRY AT MAPLETON, IL. THE FACILITY INCLUDES A HEATING PLANT WHICH CONSISTS OF 5 SPREADER STOKER BOILERS, 4 OF WHICH (BOILERS #2-#5) ARE THE SUBJECT OF THIS REFERRAL. EACH HAS A DESIGN HEAT INPUT RATE GREATER THAN 250 MILLION BTU PER HR. (MM BTU/HR) AND WAS DESIGNED AND CONSTRUCTED AFTER 8/17/71, THE EFFECTIVE DATE OF THE FEDERAL NEW SOURCE PERFORMANCE STANDARD FOR FOSSIL FUEL-FIRED STEAM GENERATORS (40 CFR PART 60, SUBPART D). REG. 5 HAS FOUND THE BOIULERS TO BE SUBJECT TO THAT STANDARD. THESE BOIL- ERS ARE SUBJECT TO IL. AIR POLLUTION CONTROL REGULATION 203(G)(1)(D), WHICH LIMITS PARTICULATE EMISSIONS FROM COM- BUSTION SOURCES BURNING SOLID FUEL CONSTRUCTED AFTER 5/31 72. RULE 203 (G)(1)(D) IS PART OF THE IL. STATE IMPLEMEN- TATION PLAN (SIP). CATERPILLAR INSTALLED MULTICLONES FOLLOWED BY DUAL ALKALI FLUE GAS DESULFURIZATION (FGD) SYSTEMS ON EACH OF MAPLETON BOILERS TO CONTROL BOTH SULFUR DIOXIDE AND PAR- TICULATE EMISSIONS. (CATERPILLAR ALSO INSTALLED THESE SYS TEMS ON 12 OTHER BOILERS LOCATED AT 4 OTHER PLANTS IN IL.) BOILERS #2 & #3 AT MAPLETON WERE COMPLETED IN LATE 1978- EARLY 1979. PERFORMANCE TESTS WERE PERFORMED ON THESE BOILERS IN JUNE-JULY 1979. THE TESTS SHOWED COMPLIANCE WITH THE NSPS SULFUR DIOXIDE LIMITATIO