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I. General Information

A. Executive Summary

1. Overview

In this rulemaking, the EPA proposes to limit GHG 

emissions from new fossil-fuel-fired power plants by 

limiting CO2 emissions. In 2009, the EPA issued a finding

that GHG air pollution may reasonably be anticipated to 

endanger Americans’ public health and welfare, now and in 

the future, by contributing to climate change. Fossilfueled power plants emit more GHG emissions than any other 

stationary source category in the United States, and among 

new GHG emissions sources, the largest individual sources 

are in this source category. This rulemaking proposes 

federal standards of performance for new fossil fuel-fired 

power plants that can be met with existing technology.

Note that in this preamble, while we refer to these 

sources, interchangeably, as power plants, steam generating 

units, affected sources, fossil-fuel-fired electric 

generating units, covered EGUs, or, simply, EGUs, the 

proposed standards apply to only those sources identified 

in Section III.A. as the affected source category.

2. Why is the EPA proposing this rule? 
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This proposed rule reflects the EPA’s common-sense

approach to reducing CO2 and other GHG emissions, which by 

causing climate change, pose a serious threat to public 

health and welfare. The EPA is focusing first on reducing 

emissions from the largest emitters through measures with 

reasonable costs. The EPA is proposing to control CO2

pollution from fossil-fuel-fired power plants because they 

are responsible for approximately 40 percent of all U.S. 

anthropogenic GHG emissions.1 Individual new power plants 

powered by coal are among the largest individual new 

sources of GHGs. Furthermore, technology exists that can be 

readily and cost-effectively used to reduce GHG emissions 

from fossil-fuel-fired power plants. Thus, this proposed 

rule is a rational first step to control GHG emissions from 

the largest-emitting stationary sources under CAA section 

111.

a. The Serious Threat of Climate Change to the Public’s 

Health and Welfare. Climate change, including global 

warming, is a significant threat to the global environment. 

The National Research Council (NRC) of the National 

 

1 From information in Table 2-1 from ‘Inventory of U. S. 

Greenhouse Gas Emissions and Sinks: 1990 – 2009’, U. S. 

Environmental Protection Agency, EPA 430-R-11-005, April 2011.
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Academies2 stated in a 2011 report, “Each additional ton of 

greenhouse gases emitted commits us to further change and 

greater risks. In the judgment of the [NRC] Committee on 

America's Climate Choices, the environmental, economic, and 

humanitarian risks of climate change indicate a pressing 

need for substantial action to limit the magnitude of 

climate change and to prepare to adapt to its impacts.”3

Action to reduce emissions is warranted because, as 

the EPA stated in its 2009 Endangerment Finding4, GHGs

endanger the public health and public welfare of current 

and future generations. The anthropogenic buildup of GHGs 

in the atmosphere is very likely (90 to 99 percent 

probability) the cause of most of the observed global 

warming over the last 50 years.

5 Based on the Endangerment 

 

2 The National Academies comprise the National Academy of 

Sciences, National Academy of Engineering, Institute of Medicine 

and National Research Council.

3 National Research Council (2011) America’s Climate Choices, 

Committee on America’s Climate Choices, Board on Atmospheric 

Sciences and Climate, Division on Earth and Life Studies, The 

National Academies Press, Washington, DC.

4 EPA, “Endangerment and Cause or Contribute Findings for 

Greenhouse Gases Under Section 202(a) of the Clean Air Act” (74 

FR 66,496; Dec. 15, 2009). 

http://epa.gov/climatechange/endangerment.html

5 Endangerment Finding at 74 FR 66,518, which notes that the 2007 

conclusion of the Intergovernmental Panel on Climate Change was 

re-confirmed by the June 2009 assessment by the U.S. Global 

Change Research Program. 
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Finding and its underlying TSD6, reasons to reduce GHG 

emissions include the following:

 The key effects of climate change observed to date and 

projected to occur in the future include, but are not 

limited to, more frequent and intense heat waves, more 

severe wildfires, degraded air quality, heavier and 

more frequent downpours and flooding, increased 

drought, greater sea level rise and storm surge, more 

intense storms, harm to water resources, continued 

ocean acidification, harm to agriculture, and harm to 

wildlife and ecosystems. 

 These effects are anticipated to result in premature 

deaths, illnesses, damage to property and 

infrastructure, and other harm to people’s welfare in 

the U.S.

 Those “most vulnerable” to climate related health 

effects, such as children, the elderly and the poor –

 

6 EPA, “Technical Support Document for Endangerment and Cause or 

Contribute Findings For Greenhouse Gases under Section 202(a) of 

the Clean Air Act, Dec. 9, 2009.” Both the Federal Register 

Notice and the TSD for Endangerment and Cause or Contribute 

Findings are found in the public docket established for the 

endangerment rulemaking, Docket No. EPA–OAR–2009–0171 and at 

http://epa.gov/climatechange/endangerment.html.
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and future generations -- face disproportionate 

risks.7

 Human-induced climate change impacts have the 

potential to be far-reaching and multidimensional, 

though not all risks and potential impacts can be 

quantified.8

 A supporting consideration is that climate change 

impacts in certain regions of the world (potentially 

leading for example to food scarcity, conflicts or 

mass migration) may exacerbate problems that raise 

humanitarian, trade and national security issues for 

the United States.9

 The TSD further notes that some risks, such as the 

extinction of many species, would be irreversible.10 Also, 

the TSD points to research on the potential for “abrupt 

changes”11 which have uncertain or low probability but high 

potential impact. The NRC has said abrupt changes are an 

 

7 Endangerment Finding, 74 FR 66498.

8 Endangerment Finding, 74 66497.

9 Endangerment Finding, 74 FR 66535.

10 Endangerment TSD, p. 136

11 Endangerment TSD, p. 75-78. The U.S. Climate Change Science 

Program defined “abrupt change” as a “large-scale change in the

climate system that takes place over a few decades or less, 

persists (or is anticipated to persist) for at least a few 

decades, and causes substantial disruptions in human and natural 

systems.” Synthesis and Assessment Product (SAP) 3.4: Abrupt 

Climate Change (2008).
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important consideration because, if triggered, they could 

occur so quickly and unexpectedly that human or natural 

systems would have difficulty adapting to them.12 Examples 

include severe drought in subtropical areas, release of 

large amounts of GHGs stored in the sea floor and frozen 

Arctic soils, and rapid disintegration of Greenland ice or 

collapse of the West Antarctic ice sheet leading to many 

feet of sea level rise.13 

The special characteristics of GHGs make it important 

to take initial steps to control the largest emissions 

categories without delay. Unlike most traditional air 

pollutants, GHGs persist in the atmosphere for time periods 

ranging from decades to millennia, depending on the gas. 

Greenhouse gases will continue to accumulate in the 

atmosphere at higher and higher concentrations each year 

unless substantial reductions in global emissions are 

achieved. The NRC notes that emissions reduction choices 

made today matter in determining the level of impacts 

experienced not just over the next few decades, but in the 

 

12 Endangerment TSD, p. 75, citing National Research Council 

(2002)

13 Endangerment TSD , pp. 76-78 
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coming centuries and millennia.14 Also, the longer that the 

U.S. and other countries take to reduce emissions, the 

steeper the future emissions reductions that will be 

required to limit global temperature increase to any given 

level.

This proposed rule to reduce GHG emissions from the 

largest U.S. stationary source category will contribute to 

the emissions reductions required to slow or reverse the 

accumulation of GHG concentrations in the atmosphere, which 

is necessary to protect against projected climate change 

impacts and risks. Reducing GHG emissions reduces the 

impacts and risks articulated in the Endangerment Finding

and TSD.

b. The High Level of GHG Emissions from Fossil-Fuel-Fired 

Power Plants and the Opportunities to Reduce these 

Emissions. Fossil-fuel-fired power plants comprise the 

largest category of stationary source GHG emissions in the 

U.S. These sources account for 60 percent of U.S. 

 

14 National Research Council (NRC) (2011). Climate Stabilization 

Targets. Committee on Stabilization Targets for Atmospheric 

Greenhouse Gas Concentrations; Board on Atmospheric Sciences and 

Climate, Division of Earth and Life Sciences, National Academy 

Press. Washington, DC.
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stationary source GHG emissions, and 32 percent of total 

U.S. GHG emissions, based on 2009 data.15

Furthermore, a range of technologies are available to 

reduce these EGU emissions. Most new power plants being 

built in the U.S. today are either natural gas-fired or are 

powered by renewable sources of energy, such as wind, and 

therefore generally produce significantly fewer emissions 

than existing coal-fired power plants. Coal-fired power 

plants can install CCS technology and can thereby limit 

their CO2 emissions per MWh generated to levels similar to, 

or even lower than, those of natural gas-fired combined 

cycle plants without CCS. Coal-fired power plants with CCS 

are being permitted and built today, albeit with 

considerable financial assistance from the federal 

government.

There are also opportunities to reduce emissions at 

existing fossil-fired plants. For instance, the efficiency 

of much of the existing generation can be improved, lower 

emitting plants can be dispatched more often, and higher 

 

15 “Inventory of US GHG Emissions and Sinks” (April 2011); 

“Regulatory Impact Analysis for the Mandatory Reporting of 

Greenhouse Gas Emissions Final Rule (GHG Reporting)” (September 

2009).
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emitting plants can co-fire fuels, such as natural gas,

with lower CO2 intensity. 

c. Alignment with Industry’s Other CAA Obligations. 

Establishing the overall regulatory requirements for GHG 

emissions from new fossil-fuel-fired power plants at this 

time is efficient because the EPA has recently issued

regulations to limit conventional pollutants (criteria and 

hazardous air pollutants) from these sources. Aligning the 

timing of these GHG rules with the rules for conventional 

pollutants gives the industry more regulatory certainty, 

will facilitate the industry’s investment decisions, and 

will help inform its compliance decisions to meet all of 

its CAA obligations.

d. Promotion of Energy Diversity. This proposed rule is 

consistent with the president’s goal to ensure that “by 

2035 we will generate 80% of our electricity from a diverse 

set of clean energy sources - including renewable energy 

sources like wind, solar, biomass and hydropower, nuclear 

power, efficient natural gas and clean coal.”16 The proposed 

rule will assist the deployment of CCS technology for new 

coal-fired power plants and create an incentive for the use 

of efficient natural gas-fired generation. Regulatory 

 

16 “Blueprint for a Secure Energy Future”, March 30, 2011
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uncertainty may be hindering the development and deployment 

of CCS, as evidenced by American Electric Power (AEP)’s

recent deferral of a large scale CCS retrofit demonstration 

project on one of its coal-fired power plants because the 

state’s utility regulators would not approve CCS without a 

regulatory requirement to reduce CO2.

17 The standard 

established in this proposal would help create the 

regulatory certainty that CCS is the path forward for new 

coal-fired generation.

3. Legal Proceedings Leading up to this Rulemaking.

In April 2007, the U.S. Supreme Court ruled, in 

Massachusetts v. EPA,

18 that GHGs meet the definition of 

“air pollutant” in the CAA. This decision clarified that 

the authorities and requirements of the CAA, including 

section 111, apply to GHG emissions.

 

17 In a July 17, 2011, press release, AEP’s chairman said, “We are

placing the project on hold until economic and policy conditions 

create a viable path forward ... We are clearly in a classic ‘which 

comes first?’ situation. The commercialization of this technology 

is vital if owners of coal-fueled generation are to comply with 

potential future climate regulations without prematurely retiring 

efficient, cost-effective generating capacity. But as a regulated 

utility, it is impossible to gain regulatory approval to recover 

our share of the costs for validating and deploying the 

technology without federal requirements to reduce greenhouse gas 

emissions already in place. The uncertainty also makes it 

difficult to attract partners to help fund the industry’s share.”

18 549 U.S. 497 (2007).
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As a result of this decision, the EPA obtained a 

voluntary remand from the U.S. Court of Appeals for the 

District of Columbia Circuit (the “Court”) to reconsider 

the EPA’s actions in a 2006 rulemaking for EGUs under CAA 

section 111, in which the EPA had promulgated standards for 

conventional air pollutants, but had declined to regulate 

GHG emissions. In part in response to threatened litigation 

over the EPA’s failure to act on the remand, the EPA agreed 

to propose today’s action to regulate GHG emissions from 

new EGUs. 

4. Legal Basis for CAA Standards for Fossil-Fired Power 

Plants. 

a. General Legal Requirements. Clean Air Act section 111 

establishes a several-step process for the EPA and the 

states to regulate air pollutants from stationary sources. 

First, the EPA must list categories of stationary sources 

that cause or contribute significantly to air pollution 

that may reasonably be anticipated to endanger public 

health or welfare. Then, the EPA must regulate emissions 

from new sources in the source category by issuing a 

standard of performance, which is defined as “a standard 

for emissions of air pollutants which reflects the degree 

of emission limitation achievable through the application 
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of the best system of emission reduction which (taking into 

account ... cost [and other factors]) ... has been 

adequately demonstrated.” New sources include new 

construction, and, as discussed below, modifications to 

existing sources as well as reconstructed sources. 

Standards of performance for new sources are often referred 

to as new source performance standards (NSPS).

Clean Air Act section 111 also requires regulation of 

existing sources of certain pollutants – in general, ones 

that are other than NAAQS pollutants or HAPs – and provides 

the states the authority to act as the direct regulators. 

Regulation of new sources of those pollutants triggers a 

requirement that EPA also promulgate emission guidelines 

for existing sources. The states must then develop 

standards of performance based on those emission guidelines 

and submit those standards in state plans to the EPA for 

approval. The states have flexibility in applying the 

standards of performance to particular sources. CAA section 

111(d)(1).

b. Cause-or-Contribute-Significantly Finding for Power 

Plants and Endangerment Finding for GHG Air Pollution. The 

EPA is authorized to regulate GHGs from power plants based 

on earlier actions concerning endangerment. Before today’s 
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rulemaking, the EPA listed different types of fossil-fuelfired EGUs as source categories that caused or contributed 

significantly to air pollution that may reasonably be 

anticipated to endanger public health or welfare. 

Specifically, the EPA listed boilers, including coal-fired 

boilers, and initially regulated them in subpart D of its 

regulations under CAA section 111. Subsequent regulation of 

utility boilers has been under subpart Da. The EPA listed 

combustion turbine engines and initially regulated them 

under subpart GG. The combustion turbine engine portions of 

combined cycle facilities were regulated under subpart GG. 

Heat recovery steam generators associated with combined 

cycle facilities with duct burners were regulated under 

either subpart Da or one of the industrial boiler 

regulations, depending on the specific characteristics of 

the heat recovery steam generator. To minimize the 

compliance burden for owners/operators of combined cycle 

facilities some monitoring harmonization was done, but 2 

subparts were still applicable. In 2005, EPA proposed 

subpart KKKK as a replacement for subpart GG and 

specifically covered the entire combined cycle facility 

under subpart KKKK such that only a single set or 

requirements would apply. In that same year, EPA proposed 
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to include Integrated Gasification Combined Cycle (IGCC)

facilities under the applicability of subpart Da. The EPA 

is authorized to promulgate the rulemaking proposed today -

- which would establish standards of performance for CO2

emissions from EGUs currently in the Da and KKKK source 

categories -- because the EPA has already determined that 

both those source categories cause or contribute 

significantly to air pollution that may reasonably be 

expected to endanger public health or welfare. Clean Air 

Act section 111 does not require the EPA, as a prerequisite 

to regulating any particular air pollutant, to issue an 

endangerment finding or a cause-or-contribute-significantly 

finding for that air pollutant from that source category. 

As an alternative, the EPA solicits comment on whether 

CAA section 111 should be interpreted to require that the 

EPA base its regulation of CO2 emissions from EGUs on two 

findings: (i) a finding that GHG air pollution may 

reasonably be anticipated to endanger public health or 

welfare; and (ii) a finding that CO2 emissions from EGUs 

cause or contribute significantly to that air pollution. If 

section 111 were so interpreted, the EPA believes that (a) 

the 2009 Endangerment Finding, along with the EPA’s 2010 

action denying petitions to reconsider that finding (which 
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action reviewed scientific developments after the 

Endangerment Finding) would fulfill any requirement to make 

the endangerment finding concerning GHG air pollution; and 

(b) the large amount of CO2 emissions from EGUs clearly 

exceeds the low applicability threshold upon which the EPA 

would make the cause-or-contribute-significantly finding.

As another alternative, the EPA solicits comment on 

whether CAA section 111 should be interpreted to require 

that the EPA base its regulation of CO2 emissions from EGUs 

on a rational basis for protection of the public health or 

welfare. If section 111 were so interpreted, the EPA 

believes that (i) its 2009 Endangerment Finding and 2010 

denial of petitions to reconsider, by themselves, and 

particularly in conjunction with the National Academy of 

Sciences’ assessment reports issued since then, coupled 

with (ii) the fact that EGUs are the largest stationary 

source emitters of CO2, provide a rational basis for 

regulating CO2 emissions from EGUs. There is no reason to 

revisit the 2009 Endangerment Finding given recent 

scientific findings that strengthen the scientific 
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conclusion that GHG air pollution endangers public health 

and welfare.19

5. Summary of Today’s Proposed Requirements to Reduce GHG 

Emissions from New Fossil-Fired Power Plants, and Rationale

for those requirements

a. Summary of Proposed Revisions to Categories and 

Requirements for New Sources 

i. Revisions to Categories of EGUs. In today’s action, the 

EPA is proposing to combine electric utility steam 

generating units (boilers) (which are currently included in 

the Da category) and combined cycle units (including IGCC 

units) that generate electricity for sale and meet certain 

size criteria (which are currently included in the KKKK 

category), into a new category for new sources (the TTTT 

category). Today’s proposed rulemaking would not affect 

conventional air pollutants or simple cycle turbines.

20

ii. Control Requirements for New Sources. The EPA is 

proposing standards of performance that require that all 

 

19 These recent scientific findings are described in section II of 

this notice, titled “Background.” See subsection II.B.3., 

“Climate Impacts Detailed in Recent NRC Assessments.” The legal 

options introduced here are presented in detail below in section 

IV.A.2, “Endangerment and Cause-or-Contribute-Significantly 

Finding.”

20 Thus, today’s rulemaking does not affect the Da and KKKK 

categories for conventional pollutants and does not affect the 

KKKK category for simple cycle turbines. 
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new fossil-fuel-fired EGUs meet an electricity-output-based 

emission rate of 1,000 lb CO2/MWh of electricity generated 

on a gross basis. This proposed standard is based on the 

demonstrated performance of natural gas combined cycle 

(NGCC) units, which are currently in wide use throughout 

the country. 

Coal-, coal refuse-, and pet-coke-fired boilers and 

IGCC units should also be able to meet this standard by 

employing CCS technology. There are a number of coal- and 

pet-coke-fired EGU projects under development that include 

CCS. While a coal unit with CCS may be more expensive than 

NGCC generation, for reasons explained below, we expect the 

difference to decrease over time as CCS becomes less 

expensive. 

Accordingly, we include in today’s proposed rulemaking 

an alternative compliance option under which affected 

sources that implement CCS could comply with the 1,000 lb 

CO2/MWh standard on a 30-year average basis. Coal- and pet 

coke-fired EGUs that use this compliance alternative must 

meet an immediate performance standard of 1,800 lb CO2/MWh 

(gross) on a 12-month rolling average basis, which can be 

achieved by a “supercritical” efficiency level, during the 

period before installation of CCS. By no later than the 11th
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year, the facility would be required to meet a reduced 

emission limit of no more than 600 lb CO2/MWh (272 kg 

CO2/MWh) (gross) on a 12-month rolling average basis for the 

remaining 20 years of the 30-year period, such that the 

weighted average CO2 emissions rate from the facility over 

the 30-year time period would be equivalent to the proposed 

standard of performance of 1,000 lb CO2/MWh. We seek comment 

on an alternative mechanism for establishing practicably 

enforceable short term limits during the 30-year period,

requiring the owner/operator to identify and obtain

approval of, at the time of construction, an alternative

30-year emission trajectory, specifying the emission rate 

for each year during the 30-year period consistent with 

meeting a 30-year average emission rate of 1,000 lb 

CO2/MWh; Under CAA section 111(b)(1)(B), the EPA is 

required to conduct a review of the new source standards in 

eight years and we intend at that time to review the 

availability and cost of CCS.

b. Rationale

Today’s proposal to combine the relevant parts of the 

Da and KKKK categories is authorized under CAA section 

111(b)(1)(A) because that provision authorizes EPA, after 

drawing up the list of affected source categories, to 
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“revise” that list from time to time. Combining the 

relevant parts of the categories, as EPA proposes to do, is 

one method to “revise” the list. Moreover, EPA’s action to 

combine is reasonable because with the combination, all new 

fossil-fuel-fired electricity generating units (and that 

meet specified minimum criteria) will be subject to the 

same requirements, and therefore will be treated alike 

because they function alike. EPA is not including simple 

cycle turbines in this rule, because they generally operate 

differently than the other units covered by today’s rule. 

The units covered by today’s rule are generally used for 

base-load or intermediate power generation, while simple 

cycle turbines are generally used much less often (and thus 

have low GHG emissions) and are used to meet peak rather 

than base or intermediate load requirements.

Today’s proposal to require an emission rate of 1,000 

lb CO2/MWh meets the requirements for a “standard of 

performance,” as defined under CAA section 111(a)(1). This 

proposed standard is based on the degree of emission 

limitation achievable through natural gas combined cycle 

(NGCC). NGCC qualifies as the “best system of emission 

reduction” (BSER) that EPA has determined has been 
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adequately demonstrated because NGCC emits the least amount 

of CO2 and does so at the least cost. 

The just-described reasons are sufficient as a legal 

matter to justify today’s proposed actions to combine 

source categories and establish the 1,000 lb CO2/MWh 

standard. Such a standard could also be met today by coalfired units using CCS. In addition, we propose to include 

the compliance alternative of allowing coal-fired power 

plants to meet either the 1000 CO2/MWh standard or to meet 

this standard over a 30-year periodso that plant developers 

can take advantage of potential advancements in CCS 

technology that could lower prices. We recognize that in 

light of the increased availability and significantly lower 

price of natural gas, energy industry modeling forecasts 

uniformly predict that few, if any, new coal-fired power 

plants will be built in the foreseeable future. Therefore, 

for these economic reasons, the new source component of the 

fossil-fuel-fired electricity generating industry is in 

effect restructuring towards gas and away from coal. 

Today’s proposed action is consistent with that trend, and 

in no way could be considered a cause of that trend. 

We recognize that some owners/operators may 

nevertheless seek to construct new coal-fired capacity. 
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This may be beneficial from the standpoint of promoting 

energy diversity, and today’s proposal does not interfere. 

In the first instance, a new coal-fired power plant may be 

able to meet the 1,000 lb CO2/MWh standard by installing CCS 

at the time of construction. At present, CCS would add 

considerably to the costs of a coal-fired power plant, but 

there are some sources of funding available through a 

limited number of government pilot programs. Because 

modeling forecasts construction of no more than a few coalfired power plants under any circumstances, those few may 

well have access to those government pilot programs.

The proposed 30-year compliance option adds additional 

flexibility for coal-fired power plants by allowing them to 

construct and begin operations, and then install CCS at 

some time in the future, as long as they install CCS at a 

time and in a manner that allows them to meet the 1,000 lb 

CO2/MWh standard over the 30-year period. 

We expect that the costs of CCS will decline in the 

future as CCS is utilized more widely. Today’s action, if 

finalized, would promote utilization of CCS by making clear 

that CCS is required for coal-fired power plants. The 

prospect of declining CCS costs, in conjunction with the 

possibility of continued availability of additional funding 
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mechanisms (e.g. pilot funding such as DOE grants, tex 

credits for investment or EOR and state incentives such as 

Clean Energy standards), indicates that CCS may be 

sufficiently accessible in the near future to the few coalfired power plants that could be expected to construct. 

Thus, the 30-year compliance option, along with the current 

opportunities for funding to install CCS immediately, 

counters any concerns that today’s action could restrict 

new coal-fired construction.

It should be noted that we are not required to justify 

the 30-year average compliance alternative on grounds that 

it qualifies as the “best system of emission reduction” 

adequately demonstrated, and we are not stating in this 

action whether that compliance alternative does or does not 

qualify as such. Thus, it is not necessary to determine 

that our expectation that costs will go down meets the 

standards for determining that CCS is “adequately 

demonstrated.” Rather, to reiterate, the 30-year 

compliance alternative, along with the opportunities to 

install CCS immediately, make clear that CCS remains 

sufficiently available for the limited number of coal-fired 

power plants that may newly construct to serve the policy 
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goals of promoting energy diversity.

21 Indeed, by clarifying 

that in the future, new coal-fired power plants will be 

required to install CCS, this rulemaking eliminates 

uncertainty about the status of coal and may well enhance 

the prospects for new coal-fired generation, and thereby 

promote energy diversity.

c. Requirements for Modifications, and Rationale. For 

purposes of today’s action, the EPA does not have a 

sufficient base of information to develop a proposal for 

the relatively few affected sources that may be expected to 

take actions that would constitute “modifications” (as 

defined under the EPA’s NSPS regulations) and therefore be 

subject to requirements for new sources. As a result, the 

EPA is not proposing requirements for NSPS modifications. 

The EPA’s current regulations define an NSPS

“modification” as a physical or operational change that 

increases the source’s maximum achievable hourly rate of 

emissions, but specifically exempt from that definition 

pollution control projects, which are projects that entail 

the installation of pollution control equipment or systems. 

The significant majority of projects that we believe EGUs 

 

21 EIA analysis (AEO 2012 early release) shows that “coal remains the dominant energy source for 

electricity generation”
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are most likely to undertake in the foreseeable future that 

could increase the maximum achievable hourly rate of CO2

emissions would constitute pollution control projects. In 

many cases, those projects would involve the installation 

of add-on control equipment required to meet CAA 

requirements for conventional air pollutants. These 

increases in CO2 emissions would generally be small and 

would occur as a chemical byproduct of the operation of the 

control equipment. In other cases, those projects would 

involve equipment changes to improve efficiency to meet the 

requirements of a future 111(b) rulemaking for existing 

sources and would have the effect of increasing a source’s 

maximum achievable hourly emission rate (lbs CO2/hr), even 

while decreasing its actual output based emission rate (lbs 

CO2/MWh). Because all of these actions would be treated as 

pollution control projects under EPA’s current NSPS 

regulations, they would be specifically exempted from the 

definition of modification.

In the past, there have been a small number of 

instances, on approximately an annual basis, in which power 

plants have undertaken actions that, in EPA’s view, should 

be treated as modifications. The sources that took these 

actions vary widely one from another, and the types of 
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actions were disparate. In light of this, we do not have 

adequate information as to the types of actions that 

qualify as modifications, the amount of increase in CO2

emissions they cause, the types of control measures, or the 

costs and effectiveness of control measures, on which to 

base a proposed standard of performance. Therefore, in 

today’s action, we are not proposing a standard of 

performance for modifications. As a result, sources that 

undertake modifications will be treated as existing sources

and thus not subject to the requirements proposed in this 

notice, although they would be subject to requirements that 

EPA intends to propose separately for existing EGUs. 

In today’s action, we solicit comment on the types of 

modifications power plants undertake and appropriate 

control measures. Depending on the information we develop, 

we may issue proposed standards of performance in the 

future.

d. Requirements for Transitional sources. The EPA is aware 

that approximately 18 proposed EGUs have received CAA 

permitting authority approval for their preconstruction 

permits, but may not have “commenced construction” by the 

date of today’s proposed rulemaking. A few of these sources 

have taken additional action preparatory to commencing 
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construction. For this proposed rule, these sources that, 

as of the date of this proposal, have a PSD permit and are 

poised to commence construction within the very near future 

are referred to as “transitional sources.” We are aware 

that approximately seven of these permitted sources are 

permitted to implement CCS to some degree. 

CAA section 111 provides by its terms that sources 

that have not “commenced construction” before the date of 

proposed standards for new sources will be subject to the 

NSPS when they do commence construction. The EPA’s 

regulations define “commenced construction” as, in general, 

undertaking a continuous program of construction or 

entering into a binding contract to do so. 40 CFR 60.2.

Commenters22 have pointed out that absent different 

treatment, transitional sources will be subject to the same 

requirements that apply to new sources that did not obtain 

their permit before the date of proposal, and these 

commenters have suggested that today’s proposed rule should 

treat transitional sources specially, in light of the 

substantial redesign that meeting such a standard would 

 

22 As mentioned elsewhere, the EPA held a series of listening sessions 

and allowed for a period of additional comment after announcing it was 

moving forward with development of new source performance standards for 

GHGs emitted from fossil fuel-fired EGUs. The term “commenters” here 

refers to those who commented during the listening sessions or during 

the subsequent comment period.
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have and the impact that redesign would have on the 

schedule for a project that was nearly ready to commence 

construction. The transitional sources at issue are coalfired EGUs that, absent special treatment, would be subject 

to the standard of performance proposed in this rulemaking. 

In today’s proposed rulemaking, the EPA is not 

proposing a standard of performance for transitional

sources, which we define as sources that a PSD permit by 

the date of this proposal and that commence construction 

within 12 months of the date of this proposal. Upon 

finalization of this rulemaking without a standard of 

performance applicable to these sources, they will not be 

treated as new sources and therefore will not be subject to 

the specific limitations set forth in the final new source 

standards. These sources would remain obligated, by the 

terms of their permits, to construct and operate in 

accordance with their permits. In addition, these sources 

will be treated as existing sources and would be subject to 

any requirements a state promulgates to meet its 

obligations under section 111(d). Sources that do not 

commence construction within 12 months of the date of this 

proposed action will be subject to the standard of 

performance for new sources. 
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e. Requirements for Reconstructed sources, and Rationale. 

The EPA’s CAA section 111 regulations provide that 

reconstructed sources are to be treated as new sources and, 

therefore, subject to new source standards of performance. 

The regulations define reconstructed sources as, in 

general, existing sources (i) that replace components to 

such an extent that the capital costs of the new components 

exceed 50 percent of the capital costs of an entirely new 

facility, and (ii) for which compliance with standards of 

performance for new sources is technologically and 

economically feasible. 40 CFR 60.15. 

Historically, we believe that very few power plants 

have undertaken reconstructions. The EPA is not aware that 

any power plants are presently planning any project that 

could meet the requirements for a reconstruction. In light 

of this limited experience concerning reconstructions, we 

lack adequate information about the type of source; the 

type of changes; the extent of emissions increases; and the 

type of control measures, including their cost and 

emissions reductions, that we need to propose a standard of 

performance for reconstructions, and we solicit comment on 

these issues.
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As a result, in today’s action, the EPA is not 

including a proposal for reconstructions and instead is 

soliciting comment on two different options. Under the 

first, we would not promulgate a standard of performance 

concerning reconstructions when we finalize this action, 

but, depending on the information we receive, we may 

propose and finalize such a standard at a later time. Under 

the second option, we would finalize a standard of 

performance. Under one sub-option, we would finalize a 

standard of 1,800 lb CO2/MWh (gross). This would be 

consistent with the first phase requirement for new sources 

availing themselves of the 30-year alternative compliance 

option. It would represent upgrading the unit to an 

efficiency level consistent with some of the best 

performing existing units. A second sub-option would treat 

reconstructed sources the same as any other new source 

(e.g. subject to an emission limit of 1,000 lb CO2/MWh). 

This sub-option could be based on the view that if the 

owner of a source plans to invest enough capital into an 

existing unit to reach the reconstructed threshold, it is 

likely with the intent of significantly increasing the life 

of the plant. The purpose would be to avoid creating an 

incentive for an owner to forego building a new clean 
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facility, in favor of merely reconstructing an existing 

facility that operated with higher emissions. . 

6. Summary of Emissions Impacts, Costs and Benefits

We are projecting that there will be no construction 

of new coal-fired generation without CCS even absent this 

proposed rule. In addition to looking at a primary case 

consistent with EIA’s primary case assumptions for electric 

demand, we also looked at a case with higher electric 

demand and another case with higher natural gas prices. We 

did not see any additional coal builds through 2030 in 

either of these cases. We also looked at a case with both 

increased natural gas prices and increased electric demand. 

In this case we saw small amounts of coal being built in 

2030. Because we did not see any new coal builds in 2020 

in any of the cases examined and we only saw small amounts 

of coal in the most extreme case examined in 2030 we do not 

project that this proposed rule will impose costs upon 

sources. While this proposed rule will not have direct 

impact on U.S. emissions of greenhouse gases, it will send 

a strong signal both domestically and internationally. 

Domestically, this proposed rule will further stimulate 

investment in CCS technology, by making it clear that such 

technology does provide a clear path forward for coal. 
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Internationally, this rule may encourage others to consider 

less GHG-intensive forms of power generation.