A U.S. Supreme Court decision leaves the Mercury and Air Toxics Standard (MATS) intact, affecting Montana’s Colstrip coal plant. The court declined a request from Republican states and energy groups to halt the rule while the D.C. Circuit Court of Appeals reviews it. The decision accelerates the timeline for Colstrip’s owners to either close the 40-year-old plant or invest significantly to meet EPA’s 2028 compliance deadline.
The EPA’s MATS rule, adopted in April, aims to cut emissions of toxic heavy metals like lead, arsenic, and mercury. Environmental and public health advocates support the rule, urging Colstrip to implement pollution controls already used by other U.S. coal plants. Robert Byron of Montana Health Professionals for a Healthy Climate has highlighted the health risks of heavy metals and fine particulate matter, which can cause cancer, strokes, and other adverse health outcomes.
The Montana Environmental Information Center hailed the court’s decision as a win for clean air rights. Derf Johnson of MEIC stated NorthWestern Energy must now confront pollution issues at Colstrip, emphasizing the harmful effects of lead and arsenic. NorthWestern Energy, a major Colstrip owner, had argued in its Supreme Court petition that MATS imposed an “untenable burden” on the plant, suggesting potential economic unfeasibility.
Without the stay, NorthWestern and co-owner Talen Montana foresee “potentially catastrophic outcomes” if forced to comply with MATS. Talen Montana, which manages the plant’s operations, continues to challenge the rule in the D.C. Circuit Court. Arguments point to the rule’s high costs and potential power grid instability without clear health benefits. However, the circuit court previously found that plaintiffs failed to meet the criteria for an emergency stay.
NorthWestern is exploring upgrades to meet compliance, asking regulators to approve funding through new tariffs. Meanwhile, NorthWestern spokesperson Jo Dee Black confirmed ongoing legal proceedings, emphasizing the MATS challenge is “not over.”
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