Emission reduction measures required to make reasonable progress toward

the national visibility goal. The owner or operator of an existing stationary source, or group of sources, shall implement emission reduction measures to make reasonable progress, as determined in accordance with title 40, Code of Federal Regulations, part 51, section 308, when required in a state implementation plan revision developed by the department. The measures shall be implemented within a reasonable timeframe after the United States environmental protection agency's approval of North Dakota’s state implementation plan revision. The measures and compliance deadline shall be determined on a source- by-source basis and shall be included in North Dakota's state implementation plan revision. All required measures shall be properly operated and maintained.