Corrosion in utility boilers, as possibly affected by combustion modifications (CM) for decreased NOx emissions, was studied at large furnaces burning high sulfur coal. Under the first part of this program, each boiler was characterized to determine the short term effects of the various combustion modifications and controls on boiler operation, and emissions. Later, a Level 1 environmental assessment (EA) of boiler operation was performed, as well as tests to measure corrosion rate within the furnace, and two 30-day continuous emission monitoring tests. This report discusses the tests performed on Boiler No. 3 at Louisville Gas and Electric (LG&E) Company's Mill Creek Generating Station in Louisville, Kentucky.