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DEQ Issues Air Quality Permit for Proposed Laurel Generating Station in Yellowstone County

  • Moira Davin
  • August 23 2021

HELENA—Today, the Montana Department of Environmental Quality released the air quality permit for NorthWestern Energy’s proposed generating station in Laurel, Mont. located in Yellowstone County. The air quality permit analyzed the potential emissions from eighteen, 9.7 megawatt-electrical reciprocating internal combustion engines, an emergency back-up diesel-fired engine generator set, a fire pump engine, natural gas line heater, and road dust at the proposed site to ensure the facility complies with the Clean Air Act of Montana.

The proposed project requires an air quality permit because the projected emissions exceed 25 tons per year for regulated pollutants, including particulate matter (PM), course particulate matter (PM10), fine particulate matter (PM2.5), oxides of nitrogen (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs). The analysis and modeling of the proposed project showed concentrations would not violate ambient air quality standards. Once issued, the permit requires NorthWestern Energy to comply with the enforceable permit conditions for the engines and take reasonable precautions for fugitive emissions, which are emissions that cannot reasonably be captured by a control system. NorthWestern Energy would have to demonstrate compliance with emission limitations for the engines through regular source testing and recordkeeping. Examples of precautions for fugitive emissions such as dust include watering the roads to minimize emissions of airborne particulate.

The proposed project is located on private land. According to the applicant, construction is estimated to begin in April of 2022 and the project would take approximately 12 months to construct.

DEQ prepared an Environmental Assessment (EA) in compliance with the Montana Environmental Policy Act. The draft permit and associated EA analyzed the potential environmental impacts of the proposed project and were published for public comment on July 9, 2021. The public comment period was extended once for an additional 15 days. The Final EA issued today includes revisions made based on comments received and responds to substantive public comments. Based on its review, DEQ determined that issuance of the air quality permit will not lead to significant adverse effects on the human or physical environment. To view the Decision Document and Final EA, please visit the DEQ website at:

There is a 15-day appeal period following the date of the Decision Document, after which the air quality permit will become final.  DEQ has not received other permit applications for this facility at this time.

Tags: Air, News and Press Release