The US Environmental Protection Agency on April 5 moved to strengthen a mercury pollution rule for coal-fired power plants after concluding the vast majority of affected generators are capable of meeting tighter emission limits.
The EPA unveiled its proposal as part of a legally required risk and technology review of the Mercury and Air Toxics Standards (MATS), an Obama-era regulation finalized in 2012 under the Clean Air Act. Mercury is a powerful neurotoxin that can stunt the brain development of young children and cause other serious health problems for adults.
US emissions of mercury and other toxic metals covered by the MATS rule, such as nickel, arsenic and lead, have declined dramatically since the regulation became effective in 2015, due in large part to a subsequent wave of coal plant retirements.
But advances in technology show that coal-fired generators with plans to operate beyond 2028 can implement additional cost-effective pollution control measures, Joseph Goffman, principal deputy assistant administrator of EPA's Office of Air and Radiation, told reporters April 5.
EPA proposal targets particulate matter emissions
The EPA's proposal would tighten existing MATS guidance for filterable particulate matter by 67%, from 0.030 lb/MMBtu down to 0.010 lb/MMBtu. The agency uses fine particulate matter as a surrogate to measure non-mercury metals covered by the MATS rule.
"Consistent with the Clean Air Act and with the information we have, we believe that the entire fleet can meet that standard," Goffman said.
Approximately 90% of coal plants expected to remain online in 2028 should be able to comply with the standard or operate at even lower emission limits, according to an EPA regulatory impact analysis.
The analysis estimated that 4.8 GW of operational coal capacity would need to either improve existing fine particulate matter controls or install new equipment to comply with the tighter standard. About 500 MW of incremental coal-fired capacity would be expected to retire by 2028 in response to the EPA's proposal, according to the agency.
The agency is also requesting comments on an even more stringent standard of 0.006 lb/MMBtu or lower. Under that standard, the EPA estimates about 22.7 GW of coal capacity would need to take some form of action. About half of that capacity would remain operational in 2028 and 12.2 GW would retire, according to the EPA.
Tighter mercury limits for lignite-fired coal plants
In addition, the EPA's proposal would tighten its mercury emission limits for lignite-fired coal plants by 70%, bringing those limits in line with mercury standards that other coal-fired units are already required to achieve.
Coal plants that burn lignite coal, otherwise known as low-ranking virgin coal, are predominantly located in Texas and North Dakota. Lignite-fired generators accounted for approximately 30% of mercury emissions from the power sector in 2021, according to EPA data.
The tighter mercury limits should not result in incremental retirements for lignite-fired units or significantly alter their projected generation levels, the EPA's analysis found.
All generators subject to the MATS update would also be required to install continuous emissions monitoring systems on their smokestacks.
"At this point, the technology has become highly cost-effective across the entire fleet, and it gives us what we believe to be the most reliable information which we and the public can access in a timely way," Goffman said.
The EPA estimated the proposal would produce between $2.4 billion to $3 billion in net monetized health and climate benefits from 2028 to 2037, with total compliance costs ranging from $230 million to $330 million. The agency's more stringent alternative is projected to yield between $6.9 billion and $9.8 billion in net benefits, with total compliance costs of between $3.4 billion and $4.6 billion.
The EPA's April 5 proposal follows a final rule issued in February in which the agency restored the legal basis for the MATS rule. In 2020, the Trump administration rescinded the rule's legal underpinning, arguing the Obama EPA gave undue weight to public health co-benefits associated with reductions in fine particulate matter.
Comments on the proposal are due 60 days after its publication in the Federal Register.
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