For the first time, the EPA is proposing to set emission limits for stationary reciprocating internal combustion engines that are not already covered by earlier EPA regulations. These engines are used at facilities such as power plants and chemical and manufacturing plants to generate electricity to power pumps and compressors. They also are used in emergencies to produce electricity and pump water for flood and fire control. This rule would apply to engines that are (1) smaller than or equal to 500 horsepower that were constructed or reconstructed before June 12, 2006, or (2) larger than or equal to 500 horsepower that were constructed or reconstructed before Dec. 19, 2002. Owners and operators of these engines would be required to retrofit engine exhaust systems with filters or catalysts.