This action amends the national emission standards for hazardous air pollutants for heat exchange systems at petroleum refineries. The amendments address issues raised in a petition for reconsideration of the EPA's final rule setting maximum achievable control technology rules for these systems and also provides additional clarity and regulatory flexibility with regard to that rule. This action does not change the level of environmental protection provided under those standards. The final amendments do not add any new cost burdens to the refining industry and may result in cost savings by establishing an additional monitoring option that sources may use in lieu of the monitoring provided in the original standard.