Legal & Regulatory

EPA Moves to Significantly Tighten Mercury and Air Toxics Standards

A proposed rule unveiled by the Environmental Protection Agency (EPA) on April 5 could considerably tighten the Mercury and Air Toxics Standards (MATS) for power plants, with specific repercussions for coal- and oil-fired generation.

The proposed rule seeks to significantly update the 2012–finalized National Emission Standards for Hazardous Air Pollutants (NESHAP) for Coal- and Oil-Fired Electric Utility Steam Generating Units—more commonly known as “MATS”—to “reflect recent developments in control technologies and performance of these plants,” the EPA said. “This proposed rule reflects the most significant improvements and updates to MATS since EPA first issued these standards in February 2012,” the agency noted.

The current MATS limit coal- and oil-fired power plant emissions of mercury and acid gas hazardous air pollutants (HAPs)—such as hydrogen chloride (HCl) and hydrogen fluoride. The standards also cover non-mercury HAP metals such as nickel, lead, and chromium, and organic HAPs such as formaldehyde and dioxin/furan.

The proposed rule sets out to implement four specific amendments to current standards:

A Tightened Standard for Non-Mercury Metal HAP Emissions at Existing Coal Plants. Existing coal plants are already subject to numeric emission limits for filterable particulate matter (fPM)—a surrogate for total non-mercury HAP metals (which the EPA chose because HAP metals are predominantly a component of particulate matter). MATS currently requires that current plants meet fPM standards of 0.030 pounds per million British thermal units (lb/MMBtu) of heat input. In the proposal, the EPA revised the fPM emission standard for existing coal plants to 0.010 lb/MMBtu. 

Mercury Standards for Lignite Power Plants. Current MATS require that lignite–fired power plants meet a mercury emission standard of 4 pounds per trillion British thermal units (lb/TBtu) or 4.0E-2 pounds per GWh. The proposal tightens that limit significantly, proposing that lignite plants must meet the same standard as existing bituminous and subbituminous plants: 1.2 lb/TBtu or 1.3E-2 lb/GWh.

A Mandate for Continuous Emissions Monitoring Systems (CEMS).  While coal and oil plants currently have the choice of demonstrating compliance for non-mercury HAP metal emissions limits by monitoring fPM via quarterly sampling or particulate matter (PM) monitoring continuous emissions monitoring systems (CEMS), the proposed rule will make it mandatory to require demonstrating compliance using PM CEMS. The EPA said it “updated information on the costs for performance testing compared to the cost of PM CEMS and capabilities of PM CEMS measurement abilities, as well as the benefits of using PM CEMS, which include increased transparency and accelerated identification of anomalous emissions.”

A Refined Definition of ‘Startup’. MATS has so far allowed two options for defining the startup period for power plants. The first option defines startup as either “the first-ever firing of fuel in a boiler for the purpose of producing electricity, or the firing of fuel in a boiler after a shutdown event for any purpose.” The second option defines startup as “the period in which operation of an [electric generating unit] is initiated for any purpose.” Because fewer than 10 power plants use the second option, the EPA is proposing to remove it.

The EPA notably also solicited public input on a “more stringent alternative” to the MATS that would implement a revised fPM standard of 0.006 lb/MMBtu and a revised mercury standard for lignite plants of 1.2 lb/TBtu. 

Costs and Impacts

According to a regulatory impact analysis associated with the rule, the proposal could result in an additional 500 MW of retired coal capacity—which is less than 1% of existing coal capacity. “Additionally, the proposed rule is not projected to result in significant coal switching between supply regions or coal rank,” the agency said.

The rule, however, will cover about 7 GW of coal capacity that is designed to burn low-rank virgin coal—or lignite—in 2028. “All of this capacity is currently equipped with Activated Carbon Injection (ACI) technology, which is designed to reduce mercury emissions, and operation of this technology for compliance with existing mercury emissions limits (e.g., MATS and other enforceable state regulations) is reflected in the baseline,” the EPA said.

The rule will also cover an additional 4.8 GW of operational coal capacity that the EPA assumes would either need to improve existing PM controls or install new PM controls to comply with proposed options. “The vast majority of that 4.8 GW is currently operating existing electrostatic precipitators (ESPs) and/or fabric filters, and nearly all of that capacity is projected to install control upgrades and remain operational in 2028,” the EPA said.

Meanwhile, under the “more stringent alternative” for which the EPA solicited public input (on a revised fPM standard of 0.006 lb/MMBtu, a revised mercury standard for lignite plants of 1.2 lb/TBtu), the agency projected 22.7 GW of coal capacity would need to take some compliance action, and only about half would remain operational with PM control upgrades in 2028.

Overall, the EPA projects industrywide compliance costs for the proposed rule of $230 million to $330 million. Net public health benefits over the EPA’s 10-year analysis period, meanwhile, are projected at between $1.2 billion to $1.9 billion.

The EPA, however, is requesting public comment on all aspects of the proposed rule, including the evaluation of the costs and efficacy of control option assumptions.

String of New Rules Part of EPA’s ‘Power Sector Strategy

The new rule joins a series of recent EPA actions that target environmental discharges from coal power plants.

Last month alone, the Biden administration finalized its Good Neighbor plan, its latest iteration of the Cross-State Air Pollution Rule (CSAPR), which the agency estimated will result in 14 GW of coal retirements. It also proposed more stringent discharge standards for three types of coal power plant wastewater as part of an update to its Effluent Limitations Guidelines (ELGs). In other actions, it proposed barring six coal-fired power plants in various states—a combined 11 GW—from disposing coal ash into unlined surface impoundments. 

In January, notably, the agency issued a proposal to reaffirm the scientific, economic, and legal underpinnings of the 2012 MATS for power plants. As part of that action, the agency sought information from the public to determine whether any new developments could warrant revisiting the MATS Residual Risk and Technology Review, which the Trump administration completed in 2020.

The MATS rule proposed on Wednesday stems from President Biden’s 2021 Executive Order 13990, which called on the EPA to consider rescinding the Trump administration’s 2020 MATS supplemental finding that it was not appropriate or necessary to regulate HAPs under Section 112 of the Clean Air Act. The proposed rule was unveiled just weeks after the Biden administration revoked the 2020 finding in February 2023, citing public risks posed by HAPs emissions.

More power plant rules are on the horizon. Later this spring, the EPA plans to release a final white paper summarizing readily available information on control techniques and measures that could potentially mitigate greenhouse gas emissions from new natural gas combustion turbines. The agency in January told POWER that it planned to propose Clean Air Act section 111 rules “that address emissions from new and existing electric generating units in spring 2023.

EPA Administrator Michael Regan in February told reporters that the rules are part of a “power sector strategy,” which seeks to align its rulemaking schedules “so that the power sector can be thoughtful about the investments that they have to make for longer-term strategic thinking around how to reduce pollution.”

A week later, Regan re-iterated the point, telling attendees at the CERAweek by S&P conference in Houston that the EPA is cognizant of rulemaking impacts. “The power sector is becoming cleaner because technology and markets are us leading there—you are leading us there, because like anyone who wants to be competitive in the future, you’re aligning investments accordingly,” he said.

“As an agency, we’re facing a mix of statutory deadlines and court-ordered deadlines—and in the past, these rules would have landed one at a time at your doorstep, creating uncertainty for investors,” he said. “That’s why we’re looking at the full suite of opportunities to marry a range of EPA authorities. We don’t have to overly rely on any one policy or rulemaking to achieve our mission and ensure affordable and reliable energy.”

The EPA is spearheading an “integrated and coordinated approach” that will allow it to tackle “full array of threats that power plants pose to clean air, safe water, and healthy land,” Regan said. That approach “also provides greater transparency, regulatory certainty for long-term investments, opportunities to reduce compliance complexity, and the right signals to create market and price stability.”

According to the EPA’s own data, however, power sector pollutant emissions have generally fallen. Annual power plant emissions data released by the EPA on Feb. 24 suggest that despite a 3% hike in power generation in the first 11 months of 2022 compared to 2021, emissions fell 6% from coal generation. Emissions from natural gas generation, however, increased by 7%, the EPA said.

Compared to 2021, the EPA’s 2022 data show a 4% decrease in nitrogen oxide (NOX) emissions, a 10% decrease in sulfur dioxide (SO2) emissions, a 1% decrease in carbon dioxide emissions, and a 3% decrease in mercury emissions.

In addition, the EPA notes ozone season (May 1 to September 30) NOX emissions decreased by 10%. “Notably, ozone season NOX emissions decreased by 21% in states covered by the current Cross-State Air Pollution Rule (CSAPR), which requires additional NOX emission reductions to facilitate attainment of the 2008 National Ambient Air Quality Standards,” the agency said.

Data collected by the Environmental Protection Agency show long-term declines in power sector emissions of nitrogen oxide, sulfur dioxide, carbon dioxide, and mercury. The agency collects the data as part of its Acid Rain Program, Cross-State Air Pollution Rule, and MATS. Source: EPA

Sonal Patel is a POWER senior associate editor (@sonalcpatel@POWERmagazine).

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