Assessment of EPA’s Utility MACT Proposal

Q: What is the EPA Utility MACT Rule?

A: The Maximum Achievable Control Technology (MACT) rule requires coal and oil-fired power plants to 

reduce emissions of mercury, other metallic toxics, acid gases, and organic air toxics. 

Q: Why is EPA proposing these regulations now?

A: EPA’s March 16, 2011 Utility MACT rule complies with a Consent Decree of the D.C. Court of Appeals 

that requires EPA to fulfill the 1990 Clean Air Act regarding hazardous air pollution from power plants. 

The Clean Air Act required EPA to determine whether such regulation is “appropriate and necessary,”

which EPA did in 2000. The Court established deadlines of March 16, 2011 for the proposed rule and 

November 16, 2011 for the final rule. 

Q: What does the rule require? 

A: Following the Clean Air Act’s approach for toxic pollutants, the rule requires “command and control” 

emission rate limits for mercury, acid gases, and particles. The limits must represent Maximum 

Achievable Control Technology, defined as the top 12% performance of existing units, which EPA set 

after collecting performance data from industry. In addition, the proposal establishes “work practice 

standards” to reduce organic air toxics, such as dioxin and furans. 

Q: How will power plants comply with the rules? 

A: A number of plants already have pollution controls that will comply with MACT limits. Others, in 

order to comply with the established emission rates, will need to install pollution controls, including 

activated carbon injection, scrubbers or dry sorbent injection, and upgrade particulate controls (see 

attached Glossary.) Nationwide, EPA projects 10 gigawatts of existing generation (1% of national 

electric generation capacity) will retire rather than install required pollution controls. This is because 

these units would no longer be economic to operate. Under a scenario of higher gas prices or greater

electric demand, fewer existing units would be expected to retire. 

Q: Why are EPA’s retirement projections so much lower than most previous studies had predicted?

A: Previous studies, including those by the North American Electric Reliability Corporation (NERC), the 

Edison Electric Institute (EEI), and several investment analysts were conducted prior to EPA’s proposal 

and made worst case estimates about what EPA was likely to require. For example, other analyses 

assumed that higher cost technology, such as scrubbers, would be required at every unit. In contrast,

EPA assumed that lower cost pollution technologies, including dry sorbent injection, will allow some 

units to comply without investing in a scrubber. These units would be able to continue operation and 
would not retire. In addition, EPA’s analysis to support the Utility MACT rule does not include 

assumptions about future regulation of coal combustion ash and cooling water, as some previous 

analyses have. Unlike EPA, some studies have also included a future carbon price that drives additional 

retirements. 

Q: How much will the rule cost?

A: EPA estimates the Utility MACT cost at $10.9 billion per year with retail electricity prices increasing 

by an average of 3.7% and consumer natural gas prices increasing by 0.6% to 1.3%. To put this into 

context, annual costs of the recently proposed Transport Rule, which will reduce sulfur dioxide and 

nitrogen oxides, is $2.8 billion. The Utility MACT is more expensive per ton of reduction than previous 

power sector rules because the cheapest reductions will already have occurred and the cost per ton 

removal increases as more reductions are required, particularly on smaller units.

Q: What are the projected health benefits of the rule?

A: Power plant air pollution, including metallic toxics such as mercury and arsenic, acid gases, and 

particles, causes several health problems, including neurological damage, cancer, lung damage, heart 

and respiratory disease, and premature death. EPA projects the benefits of reducing such emissions in

the Utility MACT rule at $59 - 160 billion per year. EPA argues that for every dollar spent on pollution 

controls, there are five to thirteen dollars in health benefits. These benefits are primarily associated 

with avoiding premature death from fine particle pollution, which is a co-benefit of the pollution 

controls used to comply with the MACT limits.

Q: Has EPA incorporated features to reduce impacts on cost and electric system reliability?

A: EPA’s recent Utility MACT proposal incorporates several flexibilities that minimize costs as well as the 

potential for disruption to electric reliability. These include work practice standards in lieu of limits for 

dioxin and furans; facility-wide averaging, which could allow some individual units to exceed MACT 

limits; sub-categorization to establish limits by boiler-type and fuel-type; exemptions for units that 

infrequently burn oil; and alternative standards that could reduce monitoring requirements. In addition, 

although the Clean Air Act generally allows 3 years to comply with MACT, EPA’s proposal emphasizes 

that states could provide waivers to allow a fourth year for facilities to install controls.

Q: Why didn’t EPA establish less stringent “health-based emission limits” for acid gases?

A: The CAA section 112(d)(4) offers an alternative "health-based emission limit (HBEL)" approach, in lieu 

of the conventional MACT approach. EPA could set a less stringent health-based emission limit, as long 

as it can ensure a margin of safety above a pollutant-specific health standard. For one of the acid gases, 

hydrogen chloride (HCl), EPA previously used this discretion to exempt sources (e.g., paper and pulp, 

lime manufacturing) from a MACT limit. EPA notes that it did not set health-based emission limits for 

acid gases in the Utility MACT rule for several reasons, including: a) lack of information on cumulative 

impacts from other respiratory irritants, environmental effects of acid gases, and significant health cobenefits of a MACT limit for acid gases (i.e., reduced premature deaths through reductions in fine 
particles). Because compliance with a less stringent health-based emissions limit could cost less, this 

may be a point of controversy going forward.

Q: Does the MACT rule address greenhouse gases?

A: The MACT rule is not designed to reduce greenhouse gases. However, because there would be some 

retirement of coal units and substitution of natural gas capacity for coal, modest reductions of 

greenhouse gases are expected. 

Glossary of Pollution Control Technologies

Activated Carbon Injection (ACI): a commercially available technology that, in combination with 

particulate controls, removes mercury from the exhaust stack of a power plant. Many units currently 

employ ACI to remove mercury in order to comply with state regulations. 

Dry Sorbent Injection (DSI): a commercially available technology (similar to ACI for mercury) that, in 

combination with particulate controls, has been shown to significantly reduce acid gases, as well as 

sulfur dioxide (SO2). DSI is currently employed on a number of existing power plants to control other 

pollutants and other companies have announced installation plans. DSI has significantly lower capital 

costs than a scrubber, but non-trivial operating costs due to the cost of sorbent. This feature makes it 

best suited for certain fuels and for smaller, less frequently operated units that want to avoid a more 

expensive scrubber and don’t need large amounts of sorbent (e.g., Trona). 

Particulate controls: Particle pollution can be captured by particulate controls installed on the exhaust 

stack of a power plant. All existing power plants have some particulate controls, namely electrostatic 

precipitators (ESP) or fabric filters/baghouses. The Utility MACT rule may require upgrades, including 

from ESP to fabric filters for some units, depending on the other controls in use and type of fuel burned. 

Scrubber or Flue Gas Desulfurization (FGD): a commercially available technology that removes SO2 as 

well as acid gases from power plant exhaust. More than half of existing coal-fired generating units 

currently have a scrubber installed for SO2 control. Variations include wet scrubbers and dry scrubbers. 

Wet scrubbers are the most expensive pollution control technology relevant to the Utility MACT 

rulemaking.

Selective Catalytic Reduction (SCR): is commercially available technology that removes nitrogen oxides 

(NOX) from power plant exhaust and is currently installed at many facilities, particularly in the eastern 

states. In combination with a wet scrubber, SCR also removes mercury.