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EPA updates air quality standards, lowers allowable amount of emitted mercury and air toxics

The updated rule will have significant impacts on emissions of lung-damaging air pollutants in Montana.



Carol Greiman – MD, Hardin | 406-679-1082 | carolgreimann@gmail.com

Robert Merchant – Pulmonologist, Billings | 406-671-5767 | merch57@gmail.com

Sarah Johnson – RN, Missoula | 509-671-2409 | sarah.johnson4@providence.org

Michelle Uberuaga – Montana Field Manager, Moms Clean Air Force | 406.223.4714 | muberuaga@momscleanairforce.org


MONTANA – The EPA today announced a new Mercury and Air Toxics Standard (MATS) that will reduce emissions of toxic air pollutants in Montana including lead and arsenic. This rule is part of a suite of updated rules intended to curb pollution from coal-fired power plants, but the MATS rule is the one that will have the most immediate impact in Montana.

Montana’s largest source of toxic air pollutants is the coal-fired power plant in Colstrip. Colstrip Unit 4 releases the highest rate of filterable particulate emissions (harmful pollutants) into the air compared to any other coal-fired unit in the country. It has struggled to meet the standard for reducing these harmful emissions (page 80). Colstrip Unit 3 also releases a significant amount of filterable particulate emissions, ranking third highest emission rate in the nation. Unlike similar coal-burning units, Colstrip Units 3 and 4 lack specific controls to limit these toxic emissions. The EPA notes that the emissions from the Colstrip plant disproportionately impact the nearby Northern Cheyenne, who have taken action in the past to address the plant’s air pollution.

The updated MATS rule will require a revised non-mercury hazardous air pollutant (HAP) metal emission standard for all existing coal-fired power plants of 0.010 pounds of fPM per million British thermal units of heat input (lb/MMBtu). The EPA cites Colstrip Unit 4’s emissions between 0.019 and 0.027lb/MMBtu and Unit 3’s between 0.017-0.018 lb/MMBtu. EPA cites that this strengthened standard will ensure that all coal-fired power plants are within regulated pollution control levels “currently achieved by the vast majority of regulated units.” 

In addition, the Colstrip plant has continuous emissions monitors (CEMs), but they currently cannot be used to enforce air quality standards. The EPA’s new MATS rule further concludes that 0.010lb/MMBtu is the lowest level currently compatible with the use of CEMS for demonstrating compliance, meaning that data from the Colstrip plant’s CEMs will be able to help enforce these standards. This restores public confidence in the emissions levels and reinforces the ability to protect air quality if those monitors indicate there are harmful emissions levels. 

“It is wonderful to see the EPA finally moving forward on this action which will save lives,” said Robert Merchant, Billings pulmonologist. “It’s been hard to see the air pollution from coal-fired power plants killing people and damaging their brains and their lungs because their corporate leaders chose not to implement 50-year-old particulate control technology. Particulate air pollution from these plants is over twice as deadly as that from other sources.”

There are 170 tangentially-fired coal fired power plants in the country that use the same technology as the Colstrip plant. All of those, except the Colstrip plant, have Electrostatic Precipitators (ESP) or Fabric Filter Baghouses (FFB), or both to control particulate pollution. The Colstrip plant is the only coal plant with a wet scrubber system that does not have either an ESP or FFB (one facility even has both). From 2012-2022, the Colstrip plant has emitted 3.3 tons of lead, 1.45 tons of arsenic, 2.1 tons of chromium, 14 tons of manganese, 2 tons of nickel, and 6 tons of selenium, all of which have considerable health impacts.

EPA projects the final rule will reduce emissions of a number of air toxins in the country by 2028, including 1,000 pounds of mercury, at least 7 tons of non-mercury HAP metals, 770 tons of fine particulate matter (PM2.5), 280 tons of nitrogen oxides (NOx), and 65,000 tons of carbon dioxide (CO2). EPA predicts that the rule will see $300 million in health benefits and $130 million in climate benefits over the 10-year period from 2028-2037. Reductions in non-mercury HAP metal emissions are expected to reduce exposure to carcinogens such as nickel, arsenic, and hexavalent chromium, all of which are emitted in large measure from the Colstrip plant.

“EPA’s decision today to update the Mercury and Air Toxics Standards means that coal plants in Montana will clean up their pollution, and that’s a really good thing for the people most directly impacted, especially kids,” said Michelle Uberuaga, Montana Field Organizer for Moms Clean Air Force. “It is also a meaningful step towards environmental justice for the Indigenous communities who bear the heaviest burden from this pollution, and it means that families and communities across Montana will be more protected from harmful contamination in our air and waterways.”

The EPA last updated the federal MATS rule in 2012. Prior to EPA’s 2012 adoption of MATS, coal-fired power plants were the largest industrial source of mercury and air toxins in the nation. The rule is intended to limit emissions of mercury as well as additional toxins such as antimony, arsenic, beryllium, cadmium, chromium, cobalt, lead, manganese, nickel, and selenium. The State of Montana implemented a rule in 2010 that limits mercury emissions from coal plants, but the Montana rule does not limit emissions of other hazardous air pollutants.

The updated MATS rule is the first step in ensuring that Montanans and nearby Tribes have the same standards for clean air as other places in the nation – and a means to monitor these emissions. 


More information:

Montana-specific fact sheet, Colstrip emissions data, comments on the draft rule from the Northern Cheyenne and NGOs can be found here.

Contact for background only: 

Anne Hedges – Policy & Legislative Director, MEIC | 406-443-2520 x 102 | ahedges@meic.org



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